/**********************************************************************

  process.c -

  $Author: usa $
  created at: Tue Aug 10 14:30:50 JST 1993

  Copyright (C) 1993-2007 Yukihiro Matsumoto
  Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
  Copyright (C) 2000  Information-technology Promotion Agency, Japan

**********************************************************************/

#include "ruby/ruby.h"
#include "ruby/io.h"
#include "ruby/util.h"
#include "internal.h"
#include "vm_core.h"

#include <stdio.h>
#include <errno.h>
#include <signal.h>
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_PROCESS_H
#include <process.h>
#endif

#include <time.h>
#include <ctype.h>

#ifndef EXIT_SUCCESS
#define EXIT_SUCCESS 0
#endif
#ifndef EXIT_FAILURE
#define EXIT_FAILURE 1
#endif

#ifdef HAVE_SYS_WAIT_H
# include <sys/wait.h>
#endif
#ifdef HAVE_SYS_RESOURCE_H
# include <sys/resource.h>
#endif
#ifdef HAVE_SYS_PARAM_H
# include <sys/param.h>
#endif
#ifndef MAXPATHLEN
# define MAXPATHLEN 1024
#endif
#include "ruby/st.h"

#ifdef __EMX__
#undef HAVE_GETPGRP
#endif

#include <sys/stat.h>

#ifdef HAVE_SYS_TIMES_H
#include <sys/times.h>
#endif

#ifdef HAVE_GRP_H
#include <grp.h>
#endif

#if defined(HAVE_TIMES) || defined(_WIN32)
static VALUE rb_cProcessTms;
#endif

#ifndef WIFEXITED
#define WIFEXITED(w)    (((w) & 0xff) == 0)
#endif
#ifndef WIFSIGNALED
#define WIFSIGNALED(w)  (((w) & 0x7f) > 0 && (((w) & 0x7f) < 0x7f))
#endif
#ifndef WIFSTOPPED
#define WIFSTOPPED(w)   (((w) & 0xff) == 0x7f)
#endif
#ifndef WEXITSTATUS
#define WEXITSTATUS(w)  (((w) >> 8) & 0xff)
#endif
#ifndef WTERMSIG
#define WTERMSIG(w)     ((w) & 0x7f)
#endif
#ifndef WSTOPSIG
#define WSTOPSIG        WEXITSTATUS
#endif

#if defined(__APPLE__) && ( defined(__MACH__) || defined(__DARWIN__) ) && !defined(__MacOS_X__)
#define __MacOS_X__ 1
#endif

#if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__bsdi__)
#define HAVE_44BSD_SETUID 1
#define HAVE_44BSD_SETGID 1
#endif

#ifdef __NetBSD__
#undef HAVE_SETRUID
#undef HAVE_SETRGID
#endif

#ifdef BROKEN_SETREUID
#define setreuid ruby_setreuid
int setreuid(rb_uid_t ruid, rb_uid_t euid);
#endif
#ifdef BROKEN_SETREGID
#define setregid ruby_setregid
int setregid(rb_gid_t rgid, rb_gid_t egid);
#endif

#if defined(HAVE_44BSD_SETUID) || defined(__MacOS_X__)
#if !defined(USE_SETREUID) && !defined(BROKEN_SETREUID)
#define OBSOLETE_SETREUID 1
#endif
#if !defined(USE_SETREGID) && !defined(BROKEN_SETREGID)
#define OBSOLETE_SETREGID 1
#endif
#endif

#define preserving_errno(stmts) \
	do {int saved_errno = errno; stmts; errno = saved_errno;} while (0)


/*
 *  call-seq:
 *     Process.pid   -> fixnum
 *
 *  Returns the process id of this process. Not available on all
 *  platforms.
 *
 *     Process.pid   #=> 27415
 */

static VALUE
get_pid(void)
{
    rb_secure(2);
    return PIDT2NUM(getpid());
}


/*
 *  call-seq:
 *     Process.ppid   -> fixnum
 *
 *  Returns the process id of the parent of this process. Returns
 *  untrustworthy value on Win32/64. Not available on all platforms.
 *
 *     puts "I am #{Process.pid}"
 *     Process.fork { puts "Dad is #{Process.ppid}" }
 *
 *  <em>produces:</em>
 *
 *     I am 27417
 *     Dad is 27417
 */

static VALUE
get_ppid(void)
{
    rb_secure(2);
    return PIDT2NUM(getppid());
}


/*********************************************************************
 *
 * Document-class: Process::Status
 *
 *  <code>Process::Status</code> encapsulates the information on the
 *  status of a running or terminated system process. The built-in
 *  variable <code>$?</code> is either +nil+ or a
 *  <code>Process::Status</code> object.
 *
 *     fork { exit 99 }   #=> 26557
 *     Process.wait       #=> 26557
 *     $?.class           #=> Process::Status
 *     $?.to_i            #=> 25344
 *     $? >> 8            #=> 99
 *     $?.stopped?        #=> false
 *     $?.exited?         #=> true
 *     $?.exitstatus      #=> 99
 *
 *  Posix systems record information on processes using a 16-bit
 *  integer.  The lower bits record the process status (stopped,
 *  exited, signaled) and the upper bits possibly contain additional
 *  information (for example the program's return code in the case of
 *  exited processes). Pre Ruby 1.8, these bits were exposed directly
 *  to the Ruby program. Ruby now encapsulates these in a
 *  <code>Process::Status</code> object. To maximize compatibility,
 *  however, these objects retain a bit-oriented interface. In the
 *  descriptions that follow, when we talk about the integer value of
 *  _stat_, we're referring to this 16 bit value.
 */

static VALUE rb_cProcessStatus;

VALUE
rb_last_status_get(void)
{
    return GET_THREAD()->last_status;
}

void
rb_last_status_set(int status, rb_pid_t pid)
{
    rb_thread_t *th = GET_THREAD();
    th->last_status = rb_obj_alloc(rb_cProcessStatus);
    rb_iv_set(th->last_status, "status", INT2FIX(status));
    rb_iv_set(th->last_status, "pid", PIDT2NUM(pid));
}

static void
rb_last_status_clear(void)
{
    GET_THREAD()->last_status = Qnil;
}

/*
 *  call-seq:
 *     stat.to_i     -> fixnum
 *     stat.to_int   -> fixnum
 *
 *  Returns the bits in _stat_ as a <code>Fixnum</code>. Poking
 *  around in these bits is platform dependent.
 *
 *     fork { exit 0xab }         #=> 26566
 *     Process.wait               #=> 26566
 *     sprintf('%04x', $?.to_i)   #=> "ab00"
 */

static VALUE
pst_to_i(VALUE st)
{
    return rb_iv_get(st, "status");
}

#define PST2INT(st) NUM2INT(pst_to_i(st))

/*
 *  call-seq:
 *     stat.pid   -> fixnum
 *
 *  Returns the process ID that this status object represents.
 *
 *     fork { exit }   #=> 26569
 *     Process.wait    #=> 26569
 *     $?.pid          #=> 26569
 */

static VALUE
pst_pid(VALUE st)
{
    return rb_attr_get(st, rb_intern("pid"));
}

static void
pst_message(VALUE str, rb_pid_t pid, int status)
{
    rb_str_catf(str, "pid %ld", (long)pid);
    if (WIFSTOPPED(status)) {
	int stopsig = WSTOPSIG(status);
	const char *signame = ruby_signal_name(stopsig);
	if (signame) {
	    rb_str_catf(str, " stopped SIG%s (signal %d)", signame, stopsig);
	}
	else {
	    rb_str_catf(str, " stopped signal %d", stopsig);
	}
    }
    if (WIFSIGNALED(status)) {
	int termsig = WTERMSIG(status);
	const char *signame = ruby_signal_name(termsig);
	if (signame) {
	    rb_str_catf(str, " SIG%s (signal %d)", signame, termsig);
	}
	else {
	    rb_str_catf(str, " signal %d", termsig);
	}
    }
    if (WIFEXITED(status)) {
	rb_str_catf(str, " exit %d", WEXITSTATUS(status));
    }
#ifdef WCOREDUMP
    if (WCOREDUMP(status)) {
	rb_str_cat2(str, " (core dumped)");
    }
#endif
}


/*
 *  call-seq:
 *     stat.to_s   -> string
 *
 *  Show pid and exit status as a string.
 *
 *    system("false")
 *    p $?.to_s         #=> "pid 12766 exit 1"
 *
 */

static VALUE
pst_to_s(VALUE st)
{
    rb_pid_t pid;
    int status;
    VALUE str;

    pid = NUM2PIDT(pst_pid(st));
    status = PST2INT(st);

    str = rb_str_buf_new(0);
    pst_message(str, pid, status);
    return str;
}


/*
 *  call-seq:
 *     stat.inspect   -> string
 *
 *  Override the inspection method.
 *
 *    system("false")
 *    p $?.inspect #=> "#<Process::Status: pid 12861 exit 1>"
 *
 */

static VALUE
pst_inspect(VALUE st)
{
    rb_pid_t pid;
    int status;
    VALUE vpid, str;

    vpid = pst_pid(st);
    if (NIL_P(vpid)) {
        return rb_sprintf("#<%s: uninitialized>", rb_class2name(CLASS_OF(st)));
    }
    pid = NUM2PIDT(vpid);
    status = PST2INT(st);

    str = rb_sprintf("#<%s: ", rb_class2name(CLASS_OF(st)));
    pst_message(str, pid, status);
    rb_str_cat2(str, ">");
    return str;
}


/*
 *  call-seq:
 *     stat == other   -> true or false
 *
 *  Returns +true+ if the integer value of _stat_
 *  equals <em>other</em>.
 */

static VALUE
pst_equal(VALUE st1, VALUE st2)
{
    if (st1 == st2) return Qtrue;
    return rb_equal(pst_to_i(st1), st2);
}


/*
 *  call-seq:
 *     stat & num   -> fixnum
 *
 *  Logical AND of the bits in _stat_ with <em>num</em>.
 *
 *     fork { exit 0x37 }
 *     Process.wait
 *     sprintf('%04x', $?.to_i)       #=> "3700"
 *     sprintf('%04x', $? & 0x1e00)   #=> "1600"
 */

static VALUE
pst_bitand(VALUE st1, VALUE st2)
{
    int status = PST2INT(st1) & NUM2INT(st2);

    return INT2NUM(status);
}


/*
 *  call-seq:
 *     stat >> num   -> fixnum
 *
 *  Shift the bits in _stat_ right <em>num</em> places.
 *
 *     fork { exit 99 }   #=> 26563
 *     Process.wait       #=> 26563
 *     $?.to_i            #=> 25344
 *     $? >> 8            #=> 99
 */

static VALUE
pst_rshift(VALUE st1, VALUE st2)
{
    int status = PST2INT(st1) >> NUM2INT(st2);

    return INT2NUM(status);
}


/*
 *  call-seq:
 *     stat.stopped?   -> true or false
 *
 *  Returns +true+ if this process is stopped. This is only
 *  returned if the corresponding <code>wait</code> call had the
 *  <code>WUNTRACED</code> flag set.
 */

static VALUE
pst_wifstopped(VALUE st)
{
    int status = PST2INT(st);

    if (WIFSTOPPED(status))
	return Qtrue;
    else
	return Qfalse;
}


/*
 *  call-seq:
 *     stat.stopsig   -> fixnum or nil
 *
 *  Returns the number of the signal that caused _stat_ to stop
 *  (or +nil+ if self is not stopped).
 */

static VALUE
pst_wstopsig(VALUE st)
{
    int status = PST2INT(st);

    if (WIFSTOPPED(status))
	return INT2NUM(WSTOPSIG(status));
    return Qnil;
}


/*
 *  call-seq:
 *     stat.signaled?   -> true or false
 *
 *  Returns +true+ if _stat_ terminated because of
 *  an uncaught signal.
 */

static VALUE
pst_wifsignaled(VALUE st)
{
    int status = PST2INT(st);

    if (WIFSIGNALED(status))
	return Qtrue;
    else
	return Qfalse;
}


/*
 *  call-seq:
 *     stat.termsig   -> fixnum or nil
 *
 *  Returns the number of the signal that caused _stat_ to
 *  terminate (or +nil+ if self was not terminated by an
 *  uncaught signal).
 */

static VALUE
pst_wtermsig(VALUE st)
{
    int status = PST2INT(st);

    if (WIFSIGNALED(status))
	return INT2NUM(WTERMSIG(status));
    return Qnil;
}


/*
 *  call-seq:
 *     stat.exited?   -> true or false
 *
 *  Returns +true+ if _stat_ exited normally (for
 *  example using an <code>exit()</code> call or finishing the
 *  program).
 */

static VALUE
pst_wifexited(VALUE st)
{
    int status = PST2INT(st);

    if (WIFEXITED(status))
	return Qtrue;
    else
	return Qfalse;
}


/*
 *  call-seq:
 *     stat.exitstatus   -> fixnum or nil
 *
 *  Returns the least significant eight bits of the return code of
 *  _stat_. Only available if <code>exited?</code> is
 *  +true+.
 *
 *     fork { }           #=> 26572
 *     Process.wait       #=> 26572
 *     $?.exited?         #=> true
 *     $?.exitstatus      #=> 0
 *
 *     fork { exit 99 }   #=> 26573
 *     Process.wait       #=> 26573
 *     $?.exited?         #=> true
 *     $?.exitstatus      #=> 99
 */

static VALUE
pst_wexitstatus(VALUE st)
{
    int status = PST2INT(st);

    if (WIFEXITED(status))
	return INT2NUM(WEXITSTATUS(status));
    return Qnil;
}


/*
 *  call-seq:
 *     stat.success?   -> true, false or nil
 *
 *  Returns +true+ if _stat_ is successful, +false+ if not.
 *  Returns +nil+ if <code>exited?</code> is not +true+.
 */

static VALUE
pst_success_p(VALUE st)
{
    int status = PST2INT(st);

    if (!WIFEXITED(status))
	return Qnil;
    return WEXITSTATUS(status) == EXIT_SUCCESS ? Qtrue : Qfalse;
}


/*
 *  call-seq:
 *     stat.coredump?   -> true or false
 *
 *  Returns +true+ if _stat_ generated a coredump
 *  when it terminated. Not available on all platforms.
 */

static VALUE
pst_wcoredump(VALUE st)
{
#ifdef WCOREDUMP
    int status = PST2INT(st);

    if (WCOREDUMP(status))
	return Qtrue;
    else
	return Qfalse;
#else
    return Qfalse;
#endif
}

#if !defined(HAVE_WAITPID) && !defined(HAVE_WAIT4)
#define NO_WAITPID
static st_table *pid_tbl;

struct wait_data {
    rb_pid_t pid;
    int status;
};

static int
wait_each(rb_pid_t pid, int status, struct wait_data *data)
{
    if (data->status != -1) return ST_STOP;

    data->pid = pid;
    data->status = status;
    return ST_DELETE;
}

static int
waitall_each(rb_pid_t pid, int status, VALUE ary)
{
    rb_last_status_set(status, pid);
    rb_ary_push(ary, rb_assoc_new(PIDT2NUM(pid), rb_last_status_get()));
    return ST_DELETE;
}
#else
struct waitpid_arg {
    rb_pid_t pid;
    int *st;
    int flags;
};
#endif

static VALUE
rb_waitpid_blocking(void *data)
{
    rb_pid_t result;
#ifndef NO_WAITPID
    struct waitpid_arg *arg = data;
#endif

#if defined NO_WAITPID
    result = wait(data);
#elif defined HAVE_WAITPID
    result = waitpid(arg->pid, arg->st, arg->flags);
#else  /* HAVE_WAIT4 */
    result = wait4(arg->pid, arg->st, arg->flags, NULL);
#endif

    return (VALUE)result;
}

rb_pid_t
rb_waitpid(rb_pid_t pid, int *st, int flags)
{
    rb_pid_t result;
#ifndef NO_WAITPID
    struct waitpid_arg arg;

  retry:
    arg.pid = pid;
    arg.st = st;
    arg.flags = flags;
    result = (rb_pid_t)rb_thread_blocking_region(rb_waitpid_blocking, &arg,
						 RUBY_UBF_PROCESS, 0);
    if (result < 0) {
	if (errno == EINTR) {
            RUBY_VM_CHECK_INTS();
            goto retry;
        }
	return (rb_pid_t)-1;
    }
#else  /* NO_WAITPID */
    if (pid_tbl) {
	st_data_t status, piddata = (st_data_t)pid;
	if (pid == (rb_pid_t)-1) {
	    struct wait_data data;
	    data.pid = (rb_pid_t)-1;
	    data.status = -1;
	    st_foreach(pid_tbl, wait_each, (st_data_t)&data);
	    if (data.status != -1) {
		rb_last_status_set(data.status, data.pid);
		return data.pid;
	    }
	}
	else if (st_delete(pid_tbl, &piddata, &status)) {
	    rb_last_status_set(*st = (int)status, pid);
	    return pid;
	}
    }

    if (flags) {
	rb_raise(rb_eArgError, "can't do waitpid with flags");
    }

    for (;;) {
	result = (rb_pid_t)rb_thread_blocking_region(rb_waitpid_blocking,
						     st, RUBY_UBF_PROCESS, 0);
	if (result < 0) {
	    if (errno == EINTR) {
		rb_thread_schedule();
		continue;
	    }
	    return (rb_pid_t)-1;
	}
	if (result == pid || pid == (rb_pid_t)-1) {
	    break;
	}
	if (!pid_tbl)
	    pid_tbl = st_init_numtable();
	st_insert(pid_tbl, pid, (st_data_t)st);
	if (!rb_thread_alone()) rb_thread_schedule();
    }
#endif
    if (result > 0) {
	rb_last_status_set(*st, result);
    }
    return result;
}


/* [MG]:FIXME: I wasn't sure how this should be done, since ::wait()
   has historically been documented as if it didn't take any arguments
   despite the fact that it's just an alias for ::waitpid(). The way I
   have it below is more truthful, but a little confusing.

   I also took the liberty of putting in the pid values, as they're
   pretty useful, and it looked as if the original 'ri' output was
   supposed to contain them after "[...]depending on the value of
   aPid:".

   The 'ansi' and 'bs' formats of the ri output don't display the
   definition list for some reason, but the plain text one does.
 */

/*
 *  call-seq:
 *     Process.wait()                     -> fixnum
 *     Process.wait(pid=-1, flags=0)      -> fixnum
 *     Process.waitpid(pid=-1, flags=0)   -> fixnum
 *
 *  Waits for a child process to exit, returns its process id, and
 *  sets <code>$?</code> to a <code>Process::Status</code> object
 *  containing information on that process. Which child it waits on
 *  depends on the value of _pid_:
 *
 *  > 0::   Waits for the child whose process ID equals _pid_.
 *
 *  0::     Waits for any child whose process group ID equals that of the
 *          calling process.
 *
 *  -1::    Waits for any child process (the default if no _pid_ is
 *          given).
 *
 *  < -1::  Waits for any child whose process group ID equals the absolute
 *          value of _pid_.
 *
 *  The _flags_ argument may be a logical or of the flag values
 *  <code>Process::WNOHANG</code> (do not block if no child available)
 *  or <code>Process::WUNTRACED</code> (return stopped children that
 *  haven't been reported). Not all flags are available on all
 *  platforms, but a flag value of zero will work on all platforms.
 *
 *  Calling this method raises a <code>SystemError</code> if there are
 *  no child processes. Not available on all platforms.
 *
 *     include Process
 *     fork { exit 99 }                 #=> 27429
 *     wait                             #=> 27429
 *     $?.exitstatus                    #=> 99
 *
 *     pid = fork { sleep 3 }           #=> 27440
 *     Time.now                         #=> 2008-03-08 19:56:16 +0900
 *     waitpid(pid, Process::WNOHANG)   #=> nil
 *     Time.now                         #=> 2008-03-08 19:56:16 +0900
 *     waitpid(pid, 0)                  #=> 27440
 *     Time.now                         #=> 2008-03-08 19:56:19 +0900
 */

static VALUE
proc_wait(int argc, VALUE *argv)
{
    VALUE vpid, vflags;
    rb_pid_t pid;
    int flags, status;

    rb_secure(2);
    flags = 0;
    if (argc == 0) {
	pid = -1;
    }
    else {
	rb_scan_args(argc, argv, "02", &vpid, &vflags);
	pid = NUM2PIDT(vpid);
	if (argc == 2 && !NIL_P(vflags)) {
	    flags = NUM2UINT(vflags);
	}
    }
    if ((pid = rb_waitpid(pid, &status, flags)) < 0)
	rb_sys_fail(0);
    if (pid == 0) {
	rb_last_status_clear();
	return Qnil;
    }
    return PIDT2NUM(pid);
}


/*
 *  call-seq:
 *     Process.wait2(pid=-1, flags=0)      -> [pid, status]
 *     Process.waitpid2(pid=-1, flags=0)   -> [pid, status]
 *
 *  Waits for a child process to exit (see Process::waitpid for exact
 *  semantics) and returns an array containing the process id and the
 *  exit status (a <code>Process::Status</code> object) of that
 *  child. Raises a <code>SystemError</code> if there are no child
 *  processes.
 *
 *     Process.fork { exit 99 }   #=> 27437
 *     pid, status = Process.wait2
 *     pid                        #=> 27437
 *     status.exitstatus          #=> 99
 */

static VALUE
proc_wait2(int argc, VALUE *argv)
{
    VALUE pid = proc_wait(argc, argv);
    if (NIL_P(pid)) return Qnil;
    return rb_assoc_new(pid, rb_last_status_get());
}


/*
 *  call-seq:
 *     Process.waitall   -> [ [pid1,status1], ...]
 *
 *  Waits for all children, returning an array of
 *  _pid_/_status_ pairs (where _status_ is a
 *  <code>Process::Status</code> object).
 *
 *     fork { sleep 0.2; exit 2 }   #=> 27432
 *     fork { sleep 0.1; exit 1 }   #=> 27433
 *     fork {            exit 0 }   #=> 27434
 *     p Process.waitall
 *
 *  <em>produces</em>:
 *
 *     [[30982, #<Process::Status: pid 30982 exit 0>],
 *      [30979, #<Process::Status: pid 30979 exit 1>],
 *      [30976, #<Process::Status: pid 30976 exit 2>]]
 */

static VALUE
proc_waitall(void)
{
    VALUE result;
    rb_pid_t pid;
    int status;

    rb_secure(2);
    result = rb_ary_new();
#ifdef NO_WAITPID
    if (pid_tbl) {
	st_foreach(pid_tbl, waitall_each, result);
    }
#else
    rb_last_status_clear();
#endif

    for (pid = -1;;) {
#ifdef NO_WAITPID
	pid = wait(&status);
#else
	pid = rb_waitpid(-1, &status, 0);
#endif
	if (pid == -1) {
	    if (errno == ECHILD)
		break;
#ifdef NO_WAITPID
	    if (errno == EINTR) {
		rb_thread_schedule();
		continue;
	    }
#endif
	    rb_sys_fail(0);
	}
#ifdef NO_WAITPID
	rb_last_status_set(status, pid);
#endif
	rb_ary_push(result, rb_assoc_new(PIDT2NUM(pid), rb_last_status_get()));
    }
    return result;
}

static inline ID
id_pid(void)
{
    ID pid;
    CONST_ID(pid, "pid");
    return pid;
}

static VALUE
detach_process_pid(VALUE thread)
{
    return rb_thread_local_aref(thread, id_pid());
}

static VALUE
detach_process_watcher(void *arg)
{
    rb_pid_t cpid, pid = (rb_pid_t)(VALUE)arg;
    int status;

    while ((cpid = rb_waitpid(pid, &status, 0)) == 0) {
	/* wait while alive */
    }
    return rb_last_status_get();
}

VALUE
rb_detach_process(rb_pid_t pid)
{
    VALUE watcher = rb_thread_create(detach_process_watcher, (void*)(VALUE)pid);
    rb_thread_local_aset(watcher, id_pid(), PIDT2NUM(pid));
    rb_define_singleton_method(watcher, "pid", detach_process_pid, 0);
    return watcher;
}


/*
 *  call-seq:
 *     Process.detach(pid)   -> thread
 *
 *  Some operating systems retain the status of terminated child
 *  processes until the parent collects that status (normally using
 *  some variant of <code>wait()</code>. If the parent never collects
 *  this status, the child stays around as a <em>zombie</em> process.
 *  <code>Process::detach</code> prevents this by setting up a
 *  separate Ruby thread whose sole job is to reap the status of the
 *  process _pid_ when it terminates. Use <code>detach</code>
 *  only when you do not intent to explicitly wait for the child to
 *  terminate.
 *
 *  The waiting thread returns the exit status of the detached process
 *  when it terminates, so you can use <code>Thread#join</code> to
 *  know the result.  If specified _pid_ is not a valid child process
 *  ID, the thread returns +nil+ immediately.
 *
 *  The waiting thread has <code>pid</code> method which returns the pid.
 *
 *  In this first example, we don't reap the first child process, so
 *  it appears as a zombie in the process status display.
 *
 *     p1 = fork { sleep 0.1 }
 *     p2 = fork { sleep 0.2 }
 *     Process.waitpid(p2)
 *     sleep 2
 *     system("ps -ho pid,state -p #{p1}")
 *
 *  <em>produces:</em>
 *
 *     27389 Z
 *
 *  In the next example, <code>Process::detach</code> is used to reap
 *  the child automatically.
 *
 *     p1 = fork { sleep 0.1 }
 *     p2 = fork { sleep 0.2 }
 *     Process.detach(p1)
 *     Process.waitpid(p2)
 *     sleep 2
 *     system("ps -ho pid,state -p #{p1}")
 *
 *  <em>(produces no output)</em>
 */

static VALUE
proc_detach(VALUE obj, VALUE pid)
{
    rb_secure(2);
    return rb_detach_process(NUM2PIDT(pid));
}

#ifndef HAVE_STRING_H
char *strtok();
#endif

static int forked_child = 0;

#ifdef SIGPIPE
static RETSIGTYPE (*saved_sigpipe_handler)(int) = 0;
#endif

#if defined(POSIX_SIGNAL)
# define signal(a,b) posix_signal((a),(b))
#endif

#ifdef SIGPIPE
static RETSIGTYPE sig_do_nothing(int sig)
{
}
#endif

static void before_exec(void)
{
    /*
     * signalmask is inherited across exec() and almost system commands don't
     * work if signalmask is blocked.
     */
    rb_enable_interrupt();

#ifdef SIGPIPE
    /*
     * Some OS commands don't initialize signal handler properly. Thus we have
     * to reset signal handler before exec(). Otherwise, system() and similar
     * child process interaction might fail. (e.g. ruby -e "system 'yes | ls'")
     * [ruby-dev:12261]
     */
    saved_sigpipe_handler = signal(SIGPIPE, sig_do_nothing);
#endif

    if (!forked_child) {
	/*
	 * On Mac OS X 10.5.x (Leopard) or earlier, exec() may return ENOTSUPP
	 * if the process have multiple threads. Therefore we have to kill
	 * internal threads temporary. [ruby-core: 10583]
	 */
	rb_thread_stop_timer_thread(0);
    }
}

static void after_exec(void)
{
    rb_thread_reset_timer_thread();
    rb_thread_start_timer_thread();

#ifdef SIGPIPE
    signal(SIGPIPE, saved_sigpipe_handler);
#endif

    forked_child = 0;
    rb_disable_interrupt();
}

#define before_fork() before_exec()
#define after_fork() (GET_THREAD()->thrown_errinfo = 0, after_exec())

#include "dln.h"

static void
security(const char *str)
{
    if (rb_env_path_tainted()) {
	if (rb_safe_level() > 0) {
	    rb_raise(rb_eSecurityError, "Insecure PATH - %s", str);
	}
    }
}

#ifdef HAVE_FORK
#define try_with_sh(prog, argv) ((saved_errno == ENOEXEC) ? exec_with_sh((prog), (argv)) : (void)0)
static void
exec_with_sh(const char *prog, char **argv)
{
    *argv = (char *)prog;
    *--argv = (char *)"sh";
    execv("/bin/sh", argv);
}
#define ARGV_COUNT(n) ((n)+1)
#else
#define try_with_sh(prog, argv) (void)0
#define ARGV_COUNT(n) (n)
#endif
#define ARGV_SIZE(n) (sizeof(char*) * ARGV_COUNT(n))
#define ALLOC_ARGV(n, v) ALLOCV_N(char*, (v), ARGV_COUNT(n))
#define ALLOC_ARGV_WITH_STR(n, v, s, l) \
    (char **)(((s) = ALLOCV_N(char, (v), ARGV_SIZE(n) + (l)) + ARGV_SIZE(n)) - ARGV_SIZE(n))

static int
proc_exec_v(char **argv, const char *prog)
{
    char fbuf[MAXPATHLEN];
#if defined(__EMX__) || defined(OS2)
    char **new_argv = NULL;
#endif

    if (!prog)
	prog = argv[0];
    prog = dln_find_exe_r(prog, 0, fbuf, sizeof(fbuf));
    if (!prog) {
	errno = ENOENT;
	return -1;
    }

#if defined(__EMX__) || defined(OS2)
    {
#define COMMAND "cmd.exe"
	char *extension;

	if ((extension = strrchr(prog, '.')) != NULL && STRCASECMP(extension, ".bat") == 0) {
	    char *p;
	    int n;

	    for (n = 0; argv[n]; n++)
		/* no-op */;
	    new_argv = ALLOC_N(char*, n + 2);
	    for (; n > 0; n--)
		new_argv[n + 1] = argv[n];
	    new_argv[1] = strcpy(ALLOC_N(char, strlen(argv[0]) + 1), argv[0]);
	    for (p = new_argv[1]; *p != '\0'; p++)
		if (*p == '/')
		    *p = '\\';
	    new_argv[0] = COMMAND;
	    argv = new_argv;
	    prog = dln_find_exe_r(argv[0], 0, fbuf, sizeof(fbuf));
	    if (!prog) {
		errno = ENOENT;
		return -1;
	    }
	}
    }
#endif /* __EMX__ */
    before_exec();
    execv(prog, argv);
    preserving_errno(try_with_sh(prog, argv); after_exec());
#if defined(__EMX__) || defined(OS2)
    if (new_argv) {
	xfree(new_argv[0]);
	xfree(new_argv);
    }
#endif
    return -1;
}

int
rb_proc_exec_n(int argc, VALUE *argv, const char *prog)
{
    char **args;
    int i;
    int ret = -1;
    VALUE v;

    args = ALLOC_ARGV(argc+1, v);
    for (i=0; i<argc; i++) {
	args[i] = RSTRING_PTR(argv[i]);
    }
    args[i] = 0;
    if (args[0]) {
	ret = proc_exec_v(args, prog);
    }
    ALLOCV_END(v);
    return -1;
}

int
rb_proc_exec(const char *str)
{
#ifndef _WIN32
    const char *s = str;
    char *ss, *t;
    char **argv, **a;
    VALUE v;
    int ret = -1;
#endif

    while (*str && ISSPACE(*str))
	str++;

#ifdef _WIN32
    before_exec();
    rb_w32_spawn(P_OVERLAY, (char *)str, 0);
    after_exec();
    return -1;
#else
    for (s=str; *s; s++) {
	if (ISSPACE(*s)) {
	    const char *p, *nl = NULL;
	    for (p = s; ISSPACE(*p); p++) {
		if (*p == '\n') nl = p;
	    }
	    if (!*p) break;
	    if (nl) s = nl;
	}
	if (*s != ' ' && !ISALPHA(*s) && strchr("*?{}[]<>()~&|\\$;'`\"\n",*s)) {
#if defined(__CYGWIN32__) || defined(__EMX__)
	    char fbuf[MAXPATHLEN];
	    char *shell = dln_find_exe_r("sh", 0, fbuf, sizeof(fbuf));
	    int status = -1;
	    before_exec();
	    if (shell)
		execl(shell, "sh", "-c", str, (char *) NULL);
	    else
		status = system(str);
	    after_exec();
	    if (status != -1)
		exit(status);
#else
	    before_exec();
	    execl("/bin/sh", "sh", "-c", str, (char *)NULL);
	    preserving_errno(after_exec());
#endif
	    return -1;
	}
    }
    a = argv = ALLOC_ARGV_WITH_STR((s-str)/2+2, v, ss, s-str+1);
    memcpy(ss, str, s-str);
    ss[s-str] = '\0';
    if ((*a++ = strtok(ss, " \t")) != 0) {
	while ((t = strtok(NULL, " \t")) != 0) {
	    *a++ = t;
	}
	*a = NULL;
    }
    if (argv[0]) {
	ret = proc_exec_v(argv, 0);
    }
    else {
	errno = ENOENT;
    }
    ALLOCV_END(v);
    return ret;
#endif	/* _WIN32 */
}

enum {
    EXEC_OPTION_PGROUP,
    EXEC_OPTION_RLIMIT,
    EXEC_OPTION_UNSETENV_OTHERS,
    EXEC_OPTION_ENV,
    EXEC_OPTION_CHDIR,
    EXEC_OPTION_UMASK,
    EXEC_OPTION_DUP2,
    EXEC_OPTION_CLOSE,
    EXEC_OPTION_OPEN,
    EXEC_OPTION_DUP2_CHILD,
    EXEC_OPTION_CLOSE_OTHERS,
    EXEC_OPTION_NEW_PGROUP
};

#if defined(_WIN32)
#define HAVE_SPAWNV 1
#endif

#if !defined(HAVE_FORK) && defined(HAVE_SPAWNV)
# define USE_SPAWNV 1
#else
# define USE_SPAWNV 0
#endif
#ifndef P_NOWAIT
# define P_NOWAIT _P_NOWAIT
#endif

#if USE_SPAWNV
#if defined(_WIN32)
#define proc_spawn_v(argv, prog) rb_w32_aspawn(P_NOWAIT, (prog), (argv))
#else
static rb_pid_t
proc_spawn_v(char **argv, char *prog)
{
    char fbuf[MAXPATHLEN];
    rb_pid_t status;

    if (!prog)
	prog = argv[0];
    security(prog);
    prog = dln_find_exe_r(prog, 0, fbuf, sizeof(fbuf));
    if (!prog)
	return -1;

    before_exec();
    status = spawnv(P_NOWAIT, prog, (const char **)argv);
    if (status == -1 && errno == ENOEXEC) {
	*argv = (char *)prog;
	*--argv = (char *)"sh";
	status = spawnv(P_NOWAIT, "/bin/sh", (const char **)argv);
	after_exec();
	if (status == -1) errno = ENOEXEC;
    }
    rb_last_status_set(status == -1 ? 127 : status, 0);
    return status;
}
#endif

static rb_pid_t
proc_spawn_n(int argc, VALUE *argv, VALUE prog, VALUE options)
{
    char **args;
    int i;
    VALUE v;
    rb_pid_t pid = -1;

    args = ALLOC_ARGV(argc + 1, v);
    for (i = 0; i < argc; i++) {
	args[i] = RSTRING_PTR(argv[i]);
    }
    args[i] = (char*) 0;
    if (args[0]) {
#if defined(_WIN32)
	DWORD flags = 0;
	if (RTEST(rb_ary_entry(options, EXEC_OPTION_NEW_PGROUP))) {
	    flags = CREATE_NEW_PROCESS_GROUP;
	}
	pid = rb_w32_aspawn_flags(P_NOWAIT, prog ? RSTRING_PTR(prog) : 0, args, flags);
#else
	pid = proc_spawn_v(args, prog ? RSTRING_PTR(prog) : 0);
#endif
    }
    ALLOCV_END(v);
    return pid;
}

#if defined(_WIN32)
#define proc_spawn(str) rb_w32_spawn(P_NOWAIT, (str), 0)
#else
static rb_pid_t
proc_spawn(char *str)
{
    char fbuf[MAXPATHLEN];
    char *s, *t;
    char **argv, **a;
    rb_pid_t status;
    VALUE v;

    for (s = str; *s; s++) {
	if (*s != ' ' && !ISALPHA(*s) && strchr("*?{}[]<>()~&|\\$;'`\"\n",*s)) {
	    char *shell = dln_find_exe_r("sh", 0, fbuf, sizeof(fbuf));
	    before_exec();
	    status = spawnl(P_NOWAIT, (shell ? shell : "/bin/sh"), "sh", "-c", str, (char*)NULL);
	    rb_last_status_set(status == -1 ? 127 : status, 0);
	    after_exec();
	    return status;
	}
    }
    a = argv = ALLOC_ARGV_WITH_STR((s - str) / 2 + 2, v, s, s - str + 1);
    strcpy(s, str);
    if (*a++ = strtok(s, " \t")) {
	while (t = strtok(NULL, " \t"))
	    *a++ = t;
	*a = NULL;
    }
    status = argv[0] ? proc_spawn_v(argv, 0) : -1;
    ALLOCV_END(v);
    return status;
}
#endif
#endif

static VALUE
hide_obj(VALUE obj)
{
    RBASIC(obj)->klass = 0;
    return obj;
}

static VALUE
check_exec_redirect_fd(VALUE v, int iskey)
{
    VALUE tmp;
    int fd;
    if (FIXNUM_P(v)) {
        fd = FIX2INT(v);
    }
    else if (SYMBOL_P(v)) {
        ID id = SYM2ID(v);
        if (id == rb_intern("in"))
            fd = 0;
        else if (id == rb_intern("out"))
            fd = 1;
        else if (id == rb_intern("err"))
            fd = 2;
        else
            goto wrong;
    }
    else if (!NIL_P(tmp = rb_check_convert_type(v, T_FILE, "IO", "to_io"))) {
        rb_io_t *fptr;
        GetOpenFile(tmp, fptr);
        if (fptr->tied_io_for_writing)
            rb_raise(rb_eArgError, "duplex IO redirection");
        fd = fptr->fd;
    }
    else {
        rb_raise(rb_eArgError, "wrong exec redirect");
    }
    if (fd < 0) {
      wrong:
        rb_raise(rb_eArgError, "negative file descriptor");
    }
#ifdef _WIN32
    else if (fd >= 3 && iskey) {
        rb_raise(rb_eArgError, "wrong file descriptor (%d)", fd);
    }
#endif
    return INT2FIX(fd);
}

static void
check_exec_redirect(VALUE key, VALUE val, VALUE options)
{
    int index;
    VALUE ary, param;
    VALUE path, flags, perm;
    ID id;

    switch (TYPE(val)) {
      case T_SYMBOL:
        id = SYM2ID(val);
        if (id == rb_intern("close")) {
            index = EXEC_OPTION_CLOSE;
            param = Qnil;
        }
        else if (id == rb_intern("in")) {
            index = EXEC_OPTION_DUP2;
            param = INT2FIX(0);
        }
        else if (id == rb_intern("out")) {
            index = EXEC_OPTION_DUP2;
            param = INT2FIX(1);
        }
        else if (id == rb_intern("err")) {
            index = EXEC_OPTION_DUP2;
            param = INT2FIX(2);
        }
        else {
            rb_raise(rb_eArgError, "wrong exec redirect symbol: %s",
                                   rb_id2name(id));
        }
        break;

      case T_FILE:
        val = check_exec_redirect_fd(val, 0);
        /* fall through */
      case T_FIXNUM:
        index = EXEC_OPTION_DUP2;
        param = val;
        break;

      case T_ARRAY:
        path = rb_ary_entry(val, 0);
        if (RARRAY_LEN(val) == 2 && SYMBOL_P(path) &&
            SYM2ID(path) == rb_intern("child")) {
            index = EXEC_OPTION_DUP2_CHILD;
            param = check_exec_redirect_fd(rb_ary_entry(val, 1), 0);
        }
        else {
            index = EXEC_OPTION_OPEN;
            FilePathValue(path);
            flags = rb_ary_entry(val, 1);
            if (NIL_P(flags))
                flags = INT2NUM(O_RDONLY);
            else if (TYPE(flags) == T_STRING)
                flags = INT2NUM(rb_io_modestr_oflags(StringValueCStr(flags)));
            else
                flags = rb_to_int(flags);
            perm = rb_ary_entry(val, 2);
            perm = NIL_P(perm) ? INT2FIX(0644) : rb_to_int(perm);
            param = hide_obj(rb_ary_new3(3, hide_obj(rb_str_dup(path)),
                                            flags, perm));
        }
        break;

      case T_STRING:
        index = EXEC_OPTION_OPEN;
        path = val;
        FilePathValue(path);
        if (TYPE(key) == T_FILE)
            key = check_exec_redirect_fd(key, 1);
        if (FIXNUM_P(key) && (FIX2INT(key) == 1 || FIX2INT(key) == 2))
            flags = INT2NUM(O_WRONLY|O_CREAT|O_TRUNC);
        else
            flags = INT2NUM(O_RDONLY);
        perm = INT2FIX(0644);
        param = hide_obj(rb_ary_new3(3, hide_obj(rb_str_dup(path)),
                                        flags, perm));
        break;

      default:
        rb_raise(rb_eArgError, "wrong exec redirect action");
    }

    ary = rb_ary_entry(options, index);
    if (NIL_P(ary)) {
        ary = hide_obj(rb_ary_new());
        rb_ary_store(options, index, ary);
    }
    if (TYPE(key) != T_ARRAY) {
        VALUE fd = check_exec_redirect_fd(key, !NIL_P(param));
        rb_ary_push(ary, hide_obj(rb_assoc_new(fd, param)));
    }
    else {
        int i, n=0;
        for (i = 0 ; i < RARRAY_LEN(key); i++) {
            VALUE v = RARRAY_PTR(key)[i];
            VALUE fd = check_exec_redirect_fd(v, !NIL_P(param));
            rb_ary_push(ary, hide_obj(rb_assoc_new(fd, param)));
            n++;
        }
    }
}

#if defined(HAVE_SETRLIMIT) && defined(NUM2RLIM)
static int rlimit_type_by_lname(const char *name);
#endif

int
rb_exec_arg_addopt(struct rb_exec_arg *e, VALUE key, VALUE val)
{
    VALUE options = e->options;
    ID id;
#if defined(HAVE_SETRLIMIT) && defined(NUM2RLIM)
    int rtype;
#endif

    rb_secure(2);

    switch (TYPE(key)) {
      case T_SYMBOL:
        id = SYM2ID(key);
#ifdef HAVE_SETPGID
        if (id == rb_intern("pgroup")) {
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_PGROUP))) {
                rb_raise(rb_eArgError, "pgroup option specified twice");
            }
            if (!RTEST(val))
                val = Qfalse;
            else if (val == Qtrue)
                val = INT2FIX(0);
            else {
                pid_t pgroup = NUM2PIDT(val);
                if (pgroup < 0) {
                    rb_raise(rb_eArgError, "negative process group ID : %ld", (long)pgroup);
                }
                val = PIDT2NUM(pgroup);
            }
            rb_ary_store(options, EXEC_OPTION_PGROUP, val);
        }
        else
#endif
#ifdef _WIN32
        if (id == rb_intern("new_pgroup")) {
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_NEW_PGROUP))) {
                rb_raise(rb_eArgError, "new_pgroup option specified twice");
            }
            val = RTEST(val) ? Qtrue : Qfalse;
            rb_ary_store(options, EXEC_OPTION_NEW_PGROUP, val);
        }
        else
#endif
#if defined(HAVE_SETRLIMIT) && defined(NUM2RLIM)
        if (strncmp("rlimit_", rb_id2name(id), 7) == 0 &&
            (rtype = rlimit_type_by_lname(rb_id2name(id)+7)) != -1) {
            VALUE ary = rb_ary_entry(options, EXEC_OPTION_RLIMIT);
            VALUE tmp, softlim, hardlim;
            if (NIL_P(ary)) {
                ary = hide_obj(rb_ary_new());
                rb_ary_store(options, EXEC_OPTION_RLIMIT, ary);
            }
            tmp = rb_check_array_type(val);
            if (!NIL_P(tmp)) {
                if (RARRAY_LEN(tmp) == 1)
                    softlim = hardlim = rb_to_int(rb_ary_entry(tmp, 0));
                else if (RARRAY_LEN(tmp) == 2) {
                    softlim = rb_to_int(rb_ary_entry(tmp, 0));
                    hardlim = rb_to_int(rb_ary_entry(tmp, 1));
                }
                else {
                    rb_raise(rb_eArgError, "wrong exec rlimit option");
                }
            }
            else {
                softlim = hardlim = rb_to_int(val);
            }
            tmp = hide_obj(rb_ary_new3(3, INT2NUM(rtype), softlim, hardlim));
            rb_ary_push(ary, tmp);
        }
        else
#endif
        if (id == rb_intern("unsetenv_others")) {
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_UNSETENV_OTHERS))) {
                rb_raise(rb_eArgError, "unsetenv_others option specified twice");
            }
            val = RTEST(val) ? Qtrue : Qfalse;
            rb_ary_store(options, EXEC_OPTION_UNSETENV_OTHERS, val);
        }
        else if (id == rb_intern("chdir")) {
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_CHDIR))) {
                rb_raise(rb_eArgError, "chdir option specified twice");
            }
            FilePathValue(val);
            rb_ary_store(options, EXEC_OPTION_CHDIR,
                                  hide_obj(rb_str_dup(val)));
        }
        else if (id == rb_intern("umask")) {
	    mode_t cmask = NUM2MODET(val);
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_UMASK))) {
                rb_raise(rb_eArgError, "umask option specified twice");
            }
            rb_ary_store(options, EXEC_OPTION_UMASK, LONG2NUM(cmask));
        }
        else if (id == rb_intern("close_others")) {
            if (!NIL_P(rb_ary_entry(options, EXEC_OPTION_CLOSE_OTHERS))) {
                rb_raise(rb_eArgError, "close_others option specified twice");
            }
            val = RTEST(val) ? Qtrue : Qfalse;
            rb_ary_store(options, EXEC_OPTION_CLOSE_OTHERS, val);
        }
        else if (id == rb_intern("in")) {
            key = INT2FIX(0);
            goto redirect;
        }
        else if (id == rb_intern("out")) {
            key = INT2FIX(1);
            goto redirect;
        }
        else if (id == rb_intern("err")) {
            key = INT2FIX(2);
            goto redirect;
        }
        else {
            rb_raise(rb_eArgError, "wrong exec option symbol: %s",
                                   rb_id2name(id));
        }
        break;

      case T_FIXNUM:
      case T_FILE:
      case T_ARRAY:
redirect:
        check_exec_redirect(key, val, options);
        break;

      default:
        rb_raise(rb_eArgError, "wrong exec option");
    }

    return ST_CONTINUE;
}

static int
check_exec_options_i(st_data_t st_key, st_data_t st_val, st_data_t arg)
{
    VALUE key = (VALUE)st_key;
    VALUE val = (VALUE)st_val;
    struct rb_exec_arg *e = (struct rb_exec_arg *)arg;
    return rb_exec_arg_addopt(e, key, val);
}

static VALUE
check_exec_fds(VALUE options)
{
    VALUE h = rb_hash_new();
    VALUE ary;
    int index, maxhint = -1;
    long i;

    for (index = EXEC_OPTION_DUP2; index <= EXEC_OPTION_DUP2_CHILD; index++) {
        ary = rb_ary_entry(options, index);
        if (NIL_P(ary))
            continue;
        for (i = 0; i < RARRAY_LEN(ary); i++) {
            VALUE elt = RARRAY_PTR(ary)[i];
            int fd = FIX2INT(RARRAY_PTR(elt)[0]);
            if (RTEST(rb_hash_lookup(h, INT2FIX(fd)))) {
                rb_raise(rb_eArgError, "fd %d specified twice", fd);
            }
            if (index == EXEC_OPTION_OPEN || index == EXEC_OPTION_DUP2)
                rb_hash_aset(h, INT2FIX(fd), Qtrue);
            else if (index == EXEC_OPTION_DUP2_CHILD)
                rb_hash_aset(h, INT2FIX(fd), RARRAY_PTR(elt)[1]);
            else /* index == EXEC_OPTION_CLOSE */
                rb_hash_aset(h, INT2FIX(fd), INT2FIX(-1));
            if (maxhint < fd)
                maxhint = fd;
            if (index == EXEC_OPTION_DUP2 || index == EXEC_OPTION_DUP2_CHILD) {
                fd = FIX2INT(RARRAY_PTR(elt)[1]);
                if (maxhint < fd)
                    maxhint = fd;
            }
        }
    }

    ary = rb_ary_entry(options, EXEC_OPTION_DUP2_CHILD);
    if (!NIL_P(ary)) {
        for (i = 0; i < RARRAY_LEN(ary); i++) {
            VALUE elt = RARRAY_PTR(ary)[i];
            int newfd = FIX2INT(RARRAY_PTR(elt)[0]);
            int oldfd = FIX2INT(RARRAY_PTR(elt)[1]);
            int lastfd = oldfd;
            VALUE val = rb_hash_lookup(h, INT2FIX(lastfd));
            long depth = 0;
            while (FIXNUM_P(val) && 0 <= FIX2INT(val)) {
                lastfd = FIX2INT(val);
                val = rb_hash_lookup(h, val);
                if (RARRAY_LEN(ary) < depth)
                    rb_raise(rb_eArgError, "cyclic child fd redirection from %d", oldfd);
                depth++;
            }
            if (val != Qtrue)
                rb_raise(rb_eArgError, "child fd %d is not redirected", oldfd);
            if (oldfd != lastfd) {
                VALUE val2;
                rb_ary_store(elt, 1, INT2FIX(lastfd));
                rb_hash_aset(h, INT2FIX(newfd), INT2FIX(lastfd));
                val = INT2FIX(oldfd);
                while (FIXNUM_P(val2 = rb_hash_lookup(h, val))) {
                    rb_hash_aset(h, val, INT2FIX(lastfd));
                    val = val2;
                }
            }
        }
    }

    if (rb_ary_entry(options, EXEC_OPTION_CLOSE_OTHERS) != Qfalse) {
        rb_ary_store(options, EXEC_OPTION_CLOSE_OTHERS, INT2FIX(maxhint));
    }
    return h;
}

static void
rb_check_exec_options(VALUE opthash, struct rb_exec_arg *e)
{
    if (RHASH_EMPTY_P(opthash))
        return;
    st_foreach(RHASH_TBL(opthash), check_exec_options_i, (st_data_t)e);
}

static int
check_exec_env_i(st_data_t st_key, st_data_t st_val, st_data_t arg)
{
    VALUE key = (VALUE)st_key;
    VALUE val = (VALUE)st_val;
    VALUE env = (VALUE)arg;
    char *k;

    k = StringValueCStr(key);
    if (strchr(k, '='))
        rb_raise(rb_eArgError, "environment name contains a equal : %s", k);

    if (!NIL_P(val))
        StringValueCStr(val);

    rb_ary_push(env, hide_obj(rb_assoc_new(key, val)));

    return ST_CONTINUE;
}

static VALUE
rb_check_exec_env(VALUE hash)
{
    VALUE env;

    env = hide_obj(rb_ary_new());
    st_foreach(RHASH_TBL(hash), check_exec_env_i, (st_data_t)env);

    return env;
}

static VALUE
rb_check_argv(int argc, VALUE *argv)
{
    VALUE tmp, prog;
    int i;
    const char *name = 0;

    if (argc == 0) {
	rb_raise(rb_eArgError, "wrong number of arguments");
    }

    prog = 0;
    tmp = rb_check_array_type(argv[0]);
    if (!NIL_P(tmp)) {
	if (RARRAY_LEN(tmp) != 2) {
	    rb_raise(rb_eArgError, "wrong first argument");
	}
	prog = RARRAY_PTR(tmp)[0];
	argv[0] = RARRAY_PTR(tmp)[1];
	SafeStringValue(prog);
	StringValueCStr(prog);
	prog = rb_str_new4(prog);
	name = RSTRING_PTR(prog);
    }
    for (i = 0; i < argc; i++) {
	SafeStringValue(argv[i]);
	argv[i] = rb_str_new4(argv[i]);
	StringValueCStr(argv[i]);
    }
    security(name ? name : RSTRING_PTR(argv[0]));
    return prog;
}

static VALUE
rb_exec_getargs(int *argc_p, VALUE **argv_p, int accept_shell, VALUE *env_ret, VALUE *opthash_ret, struct rb_exec_arg *e)
{
    VALUE hash, prog;

    if (0 < *argc_p) {
        hash = rb_check_convert_type((*argv_p)[*argc_p-1], T_HASH, "Hash", "to_hash");
        if (!NIL_P(hash)) {
            *opthash_ret = hash;
            (*argc_p)--;
        }
    }

    if (0 < *argc_p) {
        hash = rb_check_convert_type((*argv_p)[0], T_HASH, "Hash", "to_hash");
        if (!NIL_P(hash)) {
            *env_ret = hash;
            (*argc_p)--;
            (*argv_p)++;
        }
    }
    prog = rb_check_argv(*argc_p, *argv_p);
    if (!prog) {
        prog = (*argv_p)[0];
        if (accept_shell && *argc_p == 1) {
            *argc_p = 0;
            *argv_p = 0;
        }
    }
    return prog;
}

static void
rb_exec_fillarg(VALUE prog, int argc, VALUE *argv, VALUE env, VALUE opthash, struct rb_exec_arg *e)
{
    VALUE options;
    MEMZERO(e, struct rb_exec_arg, 1);
    options = hide_obj(rb_ary_new());
    e->options = options;

    if (!NIL_P(opthash)) {
        rb_check_exec_options(opthash, e);
    }
    if (!NIL_P(env)) {
        env = rb_check_exec_env(env);
        rb_ary_store(options, EXEC_OPTION_ENV, env);
    }

    e->argc = argc;
    e->argv = argv;
    e->prog = prog ? RSTRING_PTR(prog) : 0;
}

VALUE
rb_exec_arg_init(int argc, VALUE *argv, int accept_shell, struct rb_exec_arg *e)
{
    VALUE prog;
    VALUE env = Qnil, opthash = Qnil;
    prog = rb_exec_getargs(&argc, &argv, accept_shell, &env, &opthash, e);
    rb_exec_fillarg(prog, argc, argv, env, opthash, e);
    return prog;
}

void
rb_exec_arg_fixup(struct rb_exec_arg *e)
{
    e->redirect_fds = check_exec_fds(e->options);
}

/*
 *  call-seq:
 *     exec([env,] command... [,options])
 *
 *  Replaces the current process by running the given external _command_.
 *  _command..._ is one of following forms.
 *
 *    commandline                 : command line string which is passed to the standard shell
 *    cmdname, arg1, ...          : command name and one or more arguments (no shell)
 *    [cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
 *
 *  If single string is given as the command,
 *  it is taken as a command line that is subject to shell expansion before being executed.
 *
 *  The standard shell means always <code>"/bin/sh"</code> on Unix-like systems,
 *  <code>ENV["RUBYSHELL"]</code> or <code>ENV["COMSPEC"]</code> on Windows NT series, and
 *  similar.
 *
 *  If two or more +string+ given,
 *  the first is taken as a command name and
 *  the rest are passed as parameters to command with no shell expansion.
 *
 *  If a two-element array at the beginning of the command,
 *  the first element is the command to be executed,
 *  and the second argument is used as the <code>argv[0]</code> value,
 *  which may show up in process listings.
 *
 *  In order to execute the command, one of the <code>exec(2)</code>
 *  system calls is used, so the running command may inherit some of the environment
 *  of the original program (including open file descriptors).
 *  This behavior is modified by env and options.
 *  See <code>spawn</code> for details.
 *
 *  Raises SystemCallError if the command couldn't execute (typically
 *  <code>Errno::ENOENT</code> when it was not found).
 *
 *     exec "echo *"       # echoes list of files in current directory
 *     # never get here
 *
 *
 *     exec "echo", "*"    # echoes an asterisk
 *     # never get here
 */

VALUE
rb_f_exec(int argc, VALUE *argv)
{
    struct rb_exec_arg earg;
#define CHILD_ERRMSG_BUFLEN 80
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };

    rb_exec_arg_init(argc, argv, TRUE, &earg);
    if (NIL_P(rb_ary_entry(earg.options, EXEC_OPTION_CLOSE_OTHERS)))
        rb_exec_arg_addopt(&earg, ID2SYM(rb_intern("close_others")), Qfalse);
    rb_exec_arg_fixup(&earg);

    rb_exec_err(&earg, errmsg, sizeof(errmsg));
    if (errmsg[0])
        rb_sys_fail(errmsg);
    rb_sys_fail(earg.prog);
    return Qnil;		/* dummy */
}

#define ERRMSG(str) do { if (errmsg && 0 < errmsg_buflen) strlcpy(errmsg, (str), errmsg_buflen); } while (0)

/*#define DEBUG_REDIRECT*/
#if defined(DEBUG_REDIRECT)

#include <stdarg.h>

static void
ttyprintf(const char *fmt, ...)
{
    va_list ap;
    FILE *tty;
    int save = errno;
#ifdef _WIN32
    tty = fopen("con", "w");
#else
    tty = fopen("/dev/tty", "w");
#endif
    if (!tty)
        return;

    va_start(ap, fmt);
    vfprintf(tty, fmt, ap);
    va_end(ap);
    fclose(tty);
    errno = save;
}

static int
redirect_dup(int oldfd)
{
    int ret;
    ret = dup(oldfd);
    ttyprintf("dup(%d) => %d\n", oldfd, ret);
    return ret;
}
#else
#define redirect_dup(oldfd) dup(oldfd)
#endif

#if defined(DEBUG_REDIRECT) || defined(_WIN32)
static int
redirect_dup2(int oldfd, int newfd)
{
    int ret;
    ret = dup2(oldfd, newfd);
    if (newfd >= 0 && newfd <= 2)
	SetStdHandle(newfd == 0 ? STD_INPUT_HANDLE : newfd == 1 ? STD_OUTPUT_HANDLE : STD_ERROR_HANDLE, (HANDLE)rb_w32_get_osfhandle(newfd));
#if defined(DEBUG_REDIRECT)
    ttyprintf("dup2(%d, %d)\n", oldfd, newfd);
#endif
    return ret;
}
#else
#define redirect_dup2(oldfd, newfd) dup2((oldfd), (newfd))
#endif

#if defined(DEBUG_REDIRECT)
static int
redirect_close(int fd)
{
    int ret;
    ret = close(fd);
    ttyprintf("close(%d)\n", fd);
    return ret;
}

static int
redirect_open(const char *pathname, int flags, mode_t perm)
{
    int ret;
    ret = open(pathname, flags, perm);
    ttyprintf("open(\"%s\", 0x%x, 0%o) => %d\n", pathname, flags, perm, ret);
    return ret;
}

#else
#define redirect_close(fd) close(fd)
#define redirect_open(pathname, flags, perm) open((pathname), (flags), (perm))
#endif

static int
save_redirect_fd(int fd, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    if (!NIL_P(save)) {
        VALUE newary;
        int save_fd = redirect_dup(fd);
        if (save_fd == -1) {
            if (errno == EBADF)
                return 0;
            ERRMSG("dup");
            return -1;
        }
        rb_update_max_fd(save_fd);
        newary = rb_ary_entry(save, EXEC_OPTION_DUP2);
        if (NIL_P(newary)) {
            newary = hide_obj(rb_ary_new());
            rb_ary_store(save, EXEC_OPTION_DUP2, newary);
        }
        rb_ary_push(newary,
                    hide_obj(rb_assoc_new(INT2FIX(fd), INT2FIX(save_fd))));

        newary = rb_ary_entry(save, EXEC_OPTION_CLOSE);
        if (NIL_P(newary)) {
            newary = hide_obj(rb_ary_new());
            rb_ary_store(save, EXEC_OPTION_CLOSE, newary);
        }
        rb_ary_push(newary, hide_obj(rb_assoc_new(INT2FIX(save_fd), Qnil)));
    }

    return 0;
}

static VALUE
save_env_i(VALUE i, VALUE ary, int argc, VALUE *argv)
{
    rb_ary_push(ary, hide_obj(rb_ary_dup(argv[0])));
    return Qnil;
}

static void
save_env(VALUE save)
{
    if (!NIL_P(save) && NIL_P(rb_ary_entry(save, EXEC_OPTION_ENV))) {
        VALUE env = rb_const_get(rb_cObject, rb_intern("ENV"));
        if (RTEST(env)) {
            VALUE ary = hide_obj(rb_ary_new());
            rb_block_call(env, rb_intern("each"), 0, 0, save_env_i,
                          (VALUE)ary);
            rb_ary_store(save, EXEC_OPTION_ENV, ary);
        }
        rb_ary_store(save, EXEC_OPTION_UNSETENV_OTHERS, Qtrue);
    }
}

static int
intcmp(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}

static int
intrcmp(const void *a, const void *b)
{
    return *(int*)b - *(int*)a;
}

static int
run_exec_dup2(VALUE ary, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    long n, i;
    int ret;
    int extra_fd = -1;
    struct fd_pair {
        int oldfd;
        int newfd;
        long older_index;
        long num_newer;
    } *pairs = 0;

    n = RARRAY_LEN(ary);
    pairs = (struct fd_pair *)malloc(sizeof(struct fd_pair) * n);
    if (pairs == NULL) {
        ERRMSG("malloc");
        return -1;
    }

    /* initialize oldfd and newfd: O(n) */
    for (i = 0; i < n; i++) {
        VALUE elt = RARRAY_PTR(ary)[i];
        pairs[i].oldfd = FIX2INT(RARRAY_PTR(elt)[1]);
        pairs[i].newfd = FIX2INT(RARRAY_PTR(elt)[0]); /* unique */
        pairs[i].older_index = -1;
    }

    /* sort the table by oldfd: O(n log n) */
    if (!RTEST(save))
        qsort(pairs, n, sizeof(struct fd_pair), intcmp);
    else
        qsort(pairs, n, sizeof(struct fd_pair), intrcmp);

    /* initialize older_index and num_newer: O(n log n) */
    for (i = 0; i < n; i++) {
        int newfd = pairs[i].newfd;
        struct fd_pair key, *found;
        key.oldfd = newfd;
        found = bsearch(&key, pairs, n, sizeof(struct fd_pair), intcmp);
        pairs[i].num_newer = 0;
        if (found) {
            while (pairs < found && (found-1)->oldfd == newfd)
                found--;
            while (found < pairs+n && found->oldfd == newfd) {
                pairs[i].num_newer++;
                found->older_index = i;
                found++;
            }
        }
    }

    /* non-cyclic redirection: O(n) */
    for (i = 0; i < n; i++) {
        long j = i;
        while (j != -1 && pairs[j].oldfd != -1 && pairs[j].num_newer == 0) {
            if (save_redirect_fd(pairs[j].newfd, save, errmsg, errmsg_buflen) < 0)
                goto fail;
            ret = redirect_dup2(pairs[j].oldfd, pairs[j].newfd);
            if (ret == -1) {
                ERRMSG("dup2");
                goto fail;
            }
            rb_update_max_fd(pairs[j].newfd);
            pairs[j].oldfd = -1;
            j = pairs[j].older_index;
            if (j != -1)
                pairs[j].num_newer--;
        }
    }

    /* cyclic redirection: O(n) */
    for (i = 0; i < n; i++) {
        long j;
        if (pairs[i].oldfd == -1)
            continue;
        if (pairs[i].oldfd == pairs[i].newfd) { /* self cycle */
#ifdef F_GETFD
            int fd = pairs[i].oldfd;
            ret = fcntl(fd, F_GETFD);
            if (ret == -1) {
                ERRMSG("fcntl(F_GETFD)");
                goto fail;
            }
            if (ret & FD_CLOEXEC) {
                ret &= ~FD_CLOEXEC;
                ret = fcntl(fd, F_SETFD, ret);
                if (ret == -1) {
                    ERRMSG("fcntl(F_SETFD)");
                    goto fail;
                }
            }
#endif
            pairs[i].oldfd = -1;
            continue;
        }
        if (extra_fd == -1) {
            extra_fd = redirect_dup(pairs[i].oldfd);
            if (extra_fd == -1) {
                ERRMSG("dup");
                goto fail;
            }
            rb_update_max_fd(extra_fd);
        }
        else {
            ret = redirect_dup2(pairs[i].oldfd, extra_fd);
            if (ret == -1) {
                ERRMSG("dup2");
                goto fail;
            }
            rb_update_max_fd(extra_fd);
        }
        pairs[i].oldfd = extra_fd;
        j = pairs[i].older_index;
        pairs[i].older_index = -1;
        while (j != -1) {
            ret = redirect_dup2(pairs[j].oldfd, pairs[j].newfd);
            if (ret == -1) {
                ERRMSG("dup2");
                goto fail;
            }
            rb_update_max_fd(ret);
            pairs[j].oldfd = -1;
            j = pairs[j].older_index;
        }
    }
    if (extra_fd != -1) {
        ret = redirect_close(extra_fd);
        if (ret == -1) {
            ERRMSG("close");
            goto fail;
        }
    }

    xfree(pairs);
    return 0;

  fail:
    xfree(pairs);
    return -1;
}

static int
run_exec_close(VALUE ary, char *errmsg, size_t errmsg_buflen)
{
    long i;
    int ret;

    for (i = 0; i < RARRAY_LEN(ary); i++) {
        VALUE elt = RARRAY_PTR(ary)[i];
        int fd = FIX2INT(RARRAY_PTR(elt)[0]);
        ret = redirect_close(fd);
        if (ret == -1) {
            ERRMSG("close");
            return -1;
        }
    }
    return 0;
}

static int
run_exec_open(VALUE ary, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    long i;
    int ret;

    for (i = 0; i < RARRAY_LEN(ary);) {
        VALUE elt = RARRAY_PTR(ary)[i];
        int fd = FIX2INT(RARRAY_PTR(elt)[0]);
        VALUE param = RARRAY_PTR(elt)[1];
        char *path = RSTRING_PTR(RARRAY_PTR(param)[0]);
        int flags = NUM2INT(RARRAY_PTR(param)[1]);
        int perm = NUM2INT(RARRAY_PTR(param)[2]);
        int need_close = 1;
        int fd2 = redirect_open(path, flags, perm);
        if (fd2 == -1) {
            ERRMSG("open");
            return -1;
        }
        rb_update_max_fd(fd2);
        while (i < RARRAY_LEN(ary) &&
               (elt = RARRAY_PTR(ary)[i], RARRAY_PTR(elt)[1] == param)) {
            fd = FIX2INT(RARRAY_PTR(elt)[0]);
            if (fd == fd2) {
                need_close = 0;
            }
            else {
                if (save_redirect_fd(fd, save, errmsg, errmsg_buflen) < 0)
                    return -1;
                ret = redirect_dup2(fd2, fd);
                if (ret == -1) {
                    ERRMSG("dup2");
                    return -1;
                }
                rb_update_max_fd(fd);
            }
            i++;
        }
        if (need_close) {
            ret = redirect_close(fd2);
            if (ret == -1) {
                ERRMSG("close");
                return -1;
            }
        }
    }
    return 0;
}

static int
run_exec_dup2_child(VALUE ary, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    long i;
    int ret;

    for (i = 0; i < RARRAY_LEN(ary); i++) {
        VALUE elt = RARRAY_PTR(ary)[i];
        int newfd = FIX2INT(RARRAY_PTR(elt)[0]);
        int oldfd = FIX2INT(RARRAY_PTR(elt)[1]);

        if (save_redirect_fd(newfd, save, errmsg, errmsg_buflen) < 0)
            return -1;
        ret = redirect_dup2(oldfd, newfd);
        if (ret == -1) {
            ERRMSG("dup2");
            return -1;
        }
        rb_update_max_fd(newfd);
    }
    return 0;
}

#ifdef HAVE_SETPGID
static int
run_exec_pgroup(VALUE obj, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    /*
     * If FD_CLOEXEC is available, rb_fork waits the child's execve.
     * So setpgid is done in the child when rb_fork is returned in the parent.
     * No race condition, even without setpgid from the parent.
     * (Is there an environment which has setpgid but FD_CLOEXEC?)
     */
    int ret;
    pid_t pgroup;
    if (!NIL_P(save)) {
        /* maybe meaningless with no fork environment... */
        rb_ary_store(save, EXEC_OPTION_PGROUP, PIDT2NUM(getpgrp()));
    }
    pgroup = NUM2PIDT(obj);
    if (pgroup == 0) {
        pgroup = getpid();
    }
    ret = setpgid(getpid(), pgroup);
    if (ret == -1) ERRMSG("setpgid");
    return ret;
}
#endif

#if defined(HAVE_SETRLIMIT) && defined(RLIM2NUM)
static int
run_exec_rlimit(VALUE ary, VALUE save, char *errmsg, size_t errmsg_buflen)
{
    long i;
    for (i = 0; i < RARRAY_LEN(ary); i++) {
        VALUE elt = RARRAY_PTR(ary)[i];
        int rtype = NUM2INT(RARRAY_PTR(elt)[0]);
        struct rlimit rlim;
        if (!NIL_P(save)) {
            VALUE tmp, newary;
            if (getrlimit(rtype, &rlim) == -1) {
                ERRMSG("getrlimit");
                return -1;
            }
            tmp = hide_obj(rb_ary_new3(3, RARRAY_PTR(elt)[0],
                                       RLIM2NUM(rlim.rlim_cur),
                                       RLIM2NUM(rlim.rlim_max)));
            newary = rb_ary_entry(save, EXEC_OPTION_RLIMIT);
            if (NIL_P(newary)) {
                newary = hide_obj(rb_ary_new());
                rb_ary_store(save, EXEC_OPTION_RLIMIT, newary);
            }
            rb_ary_push(newary, tmp);
        }
        rlim.rlim_cur = NUM2RLIM(RARRAY_PTR(elt)[1]);
        rlim.rlim_max = NUM2RLIM(RARRAY_PTR(elt)[2]);
        if (setrlimit(rtype, &rlim) == -1) {
            ERRMSG("setrlimit");
            return -1;
        }
    }
    return 0;
}
#endif

int
rb_run_exec_options_err(const struct rb_exec_arg *e, struct rb_exec_arg *s, char *errmsg, size_t errmsg_buflen)
{
    VALUE options = e->options;
    VALUE soptions = Qnil;
    VALUE obj;

    if (!RTEST(options))
        return 0;

    if (s) {
        s->argc = 0;
        s->argv = NULL;
        s->prog = NULL;
        s->options = soptions = hide_obj(rb_ary_new());
        s->redirect_fds = Qnil;
    }

#ifdef HAVE_SETPGID
    obj = rb_ary_entry(options, EXEC_OPTION_PGROUP);
    if (RTEST(obj)) {
        if (run_exec_pgroup(obj, soptions, errmsg, errmsg_buflen) == -1)
            return -1;
    }
#endif

#if defined(HAVE_SETRLIMIT) && defined(RLIM2NUM)
    obj = rb_ary_entry(options, EXEC_OPTION_RLIMIT);
    if (!NIL_P(obj)) {
        if (run_exec_rlimit(obj, soptions, errmsg, errmsg_buflen) == -1)
            return -1;
    }
#endif

    obj = rb_ary_entry(options, EXEC_OPTION_UNSETENV_OTHERS);
    if (RTEST(obj)) {
        save_env(soptions);
        rb_env_clear();
    }

    obj = rb_ary_entry(options, EXEC_OPTION_ENV);
    if (!NIL_P(obj)) {
        long i;
        save_env(soptions);
        for (i = 0; i < RARRAY_LEN(obj); i++) {
            VALUE pair = RARRAY_PTR(obj)[i];
            VALUE key = RARRAY_PTR(pair)[0];
            VALUE val = RARRAY_PTR(pair)[1];
            if (NIL_P(val))
                ruby_setenv(StringValueCStr(key), 0);
            else
                ruby_setenv(StringValueCStr(key), StringValueCStr(val));
        }
    }

    obj = rb_ary_entry(options, EXEC_OPTION_CHDIR);
    if (!NIL_P(obj)) {
        if (!NIL_P(soptions)) {
            char *cwd = my_getcwd();
            rb_ary_store(soptions, EXEC_OPTION_CHDIR,
                         hide_obj(rb_str_new2(cwd)));
            xfree(cwd);
        }
        if (chdir(RSTRING_PTR(obj)) == -1) {
            ERRMSG("chdir");
            return -1;
        }
    }

    obj = rb_ary_entry(options, EXEC_OPTION_UMASK);
    if (!NIL_P(obj)) {
        mode_t mask = NUM2MODET(obj);
        mode_t oldmask = umask(mask); /* never fail */
        if (!NIL_P(soptions))
            rb_ary_store(soptions, EXEC_OPTION_UMASK, MODET2NUM(oldmask));
    }

    obj = rb_ary_entry(options, EXEC_OPTION_DUP2);
    if (!NIL_P(obj)) {
        if (run_exec_dup2(obj, soptions, errmsg, errmsg_buflen) == -1)
            return -1;
    }

    obj = rb_ary_entry(options, EXEC_OPTION_CLOSE);
    if (!NIL_P(obj)) {
        if (!NIL_P(soptions))
            rb_warn("cannot close fd before spawn");
        else {
            if (run_exec_close(obj, errmsg, errmsg_buflen) == -1)
                return -1;
        }
    }

#ifdef HAVE_FORK
    obj = rb_ary_entry(options, EXEC_OPTION_CLOSE_OTHERS);
    if (obj != Qfalse) {
        rb_close_before_exec(3, FIX2INT(obj), e->redirect_fds);
    }
#endif

    obj = rb_ary_entry(options, EXEC_OPTION_OPEN);
    if (!NIL_P(obj)) {
        if (run_exec_open(obj, soptions, errmsg, errmsg_buflen) == -1)
            return -1;
    }

    obj = rb_ary_entry(options, EXEC_OPTION_DUP2_CHILD);
    if (!NIL_P(obj)) {
        if (run_exec_dup2_child(obj, soptions, errmsg, errmsg_buflen) == -1)
            return -1;
    }

    return 0;
}

int
rb_run_exec_options(const struct rb_exec_arg *e, struct rb_exec_arg *s)
{
    return rb_run_exec_options_err(e, s, NULL, 0);
}

int
rb_exec_err(const struct rb_exec_arg *e, char *errmsg, size_t errmsg_buflen)
{
    int argc = e->argc;
    VALUE *argv = e->argv;
    const char *prog = e->prog;

    if (rb_run_exec_options_err(e, NULL, errmsg, errmsg_buflen) < 0) {
        return -1;
    }

    if (argc == 0) {
	rb_proc_exec(prog);
    }
    else {
	rb_proc_exec_n(argc, argv, prog);
    }
    return -1;
}

int
rb_exec(const struct rb_exec_arg *e)
{
#if !defined FD_CLOEXEC && !defined HAVE_SPAWNV
    char errmsg[80] = { '\0' };
    int ret = rb_exec_err(e, errmsg, sizeof(errmsg));
    preserving_errno(
	if (errmsg[0]) {
	    fprintf(stderr, "%s\n", errmsg);
	}
	else {
	    fprintf(stderr, "%s:%d: command not found: %s\n",
		    rb_sourcefile(), rb_sourceline(), e->prog);
	}
    );
    return ret;
#else
    return rb_exec_err(e, NULL, 0);
#endif
}

#ifdef HAVE_FORK
static int
rb_exec_atfork(void* arg, char *errmsg, size_t errmsg_buflen)
{
    rb_thread_atfork_before_exec();
    return rb_exec_err(arg, errmsg, errmsg_buflen);
}
#endif

#ifdef HAVE_FORK
#ifdef FD_CLOEXEC
#if SIZEOF_INT == SIZEOF_LONG
#define proc_syswait (VALUE (*)(VALUE))rb_syswait
#else
static VALUE
proc_syswait(VALUE pid)
{
    rb_syswait((int)pid);
    return Qnil;
}
#endif
#endif

static int
move_fds_to_avoid_crash(int *fdp, int n, VALUE fds)
{
    long min = 0;
    int i;
    for (i = 0; i < n; i++) {
        int ret;
        while (RTEST(rb_hash_lookup(fds, INT2FIX(fdp[i])))) {
            if (min <= fdp[i])
                min = fdp[i]+1;
            while (RTEST(rb_hash_lookup(fds, INT2FIX(min))))
                min++;
            ret = fcntl(fdp[i], F_DUPFD, min);
            if (ret == -1)
                return -1;
            rb_update_max_fd(ret);
            close(fdp[i]);
            fdp[i] = ret;
        }
    }
    return 0;
}

static int
pipe_nocrash(int filedes[2], VALUE fds)
{
    int ret;
    ret = rb_pipe(filedes);
    if (ret == -1)
        return -1;
    if (RTEST(fds)) {
        int save = errno;
        if (move_fds_to_avoid_crash(filedes, 2, fds) == -1) {
            close(filedes[0]);
            close(filedes[1]);
            return -1;
        }
        errno = save;
    }
    return ret;
}

struct chfunc_protect_t {
    int (*chfunc)(void*, char *, size_t);
    void *arg;
    char *errmsg;
    size_t buflen;
};

static VALUE
chfunc_protect(VALUE arg)
{
    struct chfunc_protect_t *p = (struct chfunc_protect_t *)arg;

    return (VALUE)(*p->chfunc)(p->arg, p->errmsg, p->buflen);
}

#ifndef O_BINARY
#define O_BINARY 0
#endif

/*
 * Forks child process, and returns the process ID in the parent
 * process.
 *
 * If +status+ is given, protects from any exceptions and sets the
 * jump status to it.
 *
 * In the child process, just returns 0 if +chfunc+ is +NULL+.
 * Otherwise +chfunc+ will be called with +charg+, and then the child
 * process exits with +EXIT_SUCCESS+ when it returned zero.
 *
 * In the case of the function is called and returns non-zero value,
 * the child process exits with non-+EXIT_SUCCESS+ value (normally
 * 127).  And, on the platforms where +FD_CLOEXEC+ is available,
 * +errno+ is propagated to the parent process, and this function
 * returns -1 in the parent process.  On the other platforms, just
 * returns pid.
 *
 * If fds is not Qnil, internal pipe for the errno propagation is
 * arranged to avoid conflicts of the hash keys in +fds+.
 *
 * +chfunc+ must not raise any exceptions.
 */
rb_pid_t
rb_fork_err(int *status, int (*chfunc)(void*, char *, size_t), void *charg, VALUE fds,
        char *errmsg, size_t errmsg_buflen)
{
    rb_pid_t pid;
    int err, state = 0;
#ifdef FD_CLOEXEC
    int ep[2];
    VALUE io = Qnil;
#endif

#define prefork() (		\
	rb_io_flush(rb_stdout), \
	rb_io_flush(rb_stderr)	\
	)
    prefork();

#ifdef FD_CLOEXEC
    if (chfunc) {
	if (pipe_nocrash(ep, fds)) return -1;
	if (fcntl(ep[1], F_SETFD, FD_CLOEXEC)) {
	    preserving_errno((close(ep[0]), close(ep[1])));
	    return -1;
	}
    }
#endif
    for (; before_fork(), (pid = fork()) < 0; prefork()) {
	after_fork();
	switch (errno) {
	  case EAGAIN:
#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
	  case EWOULDBLOCK:
#endif
	    if (!status && !chfunc) {
		rb_thread_sleep(1);
		continue;
	    }
	    else {
		rb_protect((VALUE (*)())rb_thread_sleep, 1, &state);
		if (status) *status = state;
		if (!state) continue;
	    }
	  default:
#ifdef FD_CLOEXEC
	    if (chfunc) {
		preserving_errno((close(ep[0]), close(ep[1])));
	    }
#endif
	    if (state && !status) rb_jump_tag(state);
	    return -1;
	}
    }
    if (!pid) {
        forked_child = 1;
	if (chfunc) {
	    struct chfunc_protect_t arg;
	    arg.chfunc = chfunc;
	    arg.arg = charg;
	    arg.errmsg = errmsg;
	    arg.buflen = errmsg_buflen;
#ifdef FD_CLOEXEC
	    close(ep[0]);
#endif
	    if (!(int)rb_protect(chfunc_protect, (VALUE)&arg, &state)) _exit(EXIT_SUCCESS);
#ifdef FD_CLOEXEC
	    if (write(ep[1], &state, sizeof(state)) == sizeof(state) && state) {
		VALUE errinfo = rb_errinfo();
		io = rb_io_fdopen(ep[1], O_WRONLY|O_BINARY, NULL);
		rb_marshal_dump(errinfo, io);
		rb_io_flush(io);
	    }
	    err = errno;
	    if (write(ep[1], &err, sizeof(err)) < 0) err = errno;
            if (errmsg && 0 < errmsg_buflen) {
                errmsg[errmsg_buflen-1] = '\0';
                errmsg_buflen = strlen(errmsg);
		if (errmsg_buflen > 0 &&write(ep[1], errmsg, errmsg_buflen) < 0)
		    err = errno;
            }
	    if (!NIL_P(io)) rb_io_close(io);
#endif
#if EXIT_SUCCESS == 127
	    _exit(EXIT_FAILURE);
#else
	    _exit(127);
#endif
	}
    }
    after_fork();
#ifdef FD_CLOEXEC
    if (pid && chfunc) {
	ssize_t size;
	VALUE exc = Qnil;
	close(ep[1]);
	if ((read(ep[0], &state, sizeof(state))) == sizeof(state) && state) {
	    io = rb_io_fdopen(ep[0], O_RDONLY|O_BINARY, NULL);
	    exc = rb_marshal_load(io);
	    rb_set_errinfo(exc);
	}
#define READ_FROM_CHILD(ptr, len) \
	(NIL_P(io) ? read(ep[0], (ptr), (len)) : rb_io_bufread(io, (ptr), (len)))
	if ((size = READ_FROM_CHILD(&err, sizeof(err))) < 0) {
	    err = errno;
	}
        if (size == sizeof(err) &&
            errmsg && 0 < errmsg_buflen) {
	    ssize_t ret = READ_FROM_CHILD(errmsg, errmsg_buflen-1);
            if (0 <= ret) {
                errmsg[ret] = '\0';
            }
        }
	if (NIL_P(io))
	    close(ep[0]);
	else
	    rb_io_close(io);
	if (state || size) {
	    if (status) {
		*status = state;
		rb_protect(proc_syswait, (VALUE)pid, status);
	    }
	    else {
		rb_syswait(pid);
		if (state) rb_exc_raise(exc);
	    }
	    errno = err;
	    return -1;
	}
    }
#endif
    return pid;
}

struct chfunc_wrapper_t {
    int (*chfunc)(void*);
    void *arg;
};

static int
chfunc_wrapper(void *arg_, char *errmsg, size_t errmsg_buflen)
{
    struct chfunc_wrapper_t *arg = arg_;
    return arg->chfunc(arg->arg);
}

rb_pid_t
rb_fork(int *status, int (*chfunc)(void*), void *charg, VALUE fds)
{
    if (chfunc) {
        struct chfunc_wrapper_t warg;
        warg.chfunc = chfunc;
        warg.arg = charg;
        return rb_fork_err(status, chfunc_wrapper, &warg, fds, NULL, 0);
    }
    else {
        return rb_fork_err(status, NULL, NULL, fds, NULL, 0);
    }

}

#endif

#if defined(HAVE_FORK) && !defined(CANNOT_FORK_WITH_PTHREAD)
/*
 *  call-seq:
 *     Kernel.fork  [{ block }]   -> fixnum or nil
 *     Process.fork [{ block }]   -> fixnum or nil
 *
 *  Creates a subprocess. If a block is specified, that block is run
 *  in the subprocess, and the subprocess terminates with a status of
 *  zero. Otherwise, the +fork+ call returns twice, once in
 *  the parent, returning the process ID of the child, and once in
 *  the child, returning _nil_. The child process can exit using
 *  <code>Kernel.exit!</code> to avoid running any
 *  <code>at_exit</code> functions. The parent process should
 *  use <code>Process.wait</code> to collect the termination statuses
 *  of its children or use <code>Process.detach</code> to register
 *  disinterest in their status; otherwise, the operating system
 *  may accumulate zombie processes.
 *
 *  The thread calling fork is the only thread in the created child process.
 *  fork doesn't copy other threads.
 *
 *  If fork is not usable, Process.respond_to?(:fork) returns false.
 */

static VALUE
rb_f_fork(VALUE obj)
{
    rb_pid_t pid;

    rb_secure(2);

    switch (pid = rb_fork(0, 0, 0, Qnil)) {
      case 0:
	rb_thread_atfork();
	if (rb_block_given_p()) {
	    int status;

	    rb_protect(rb_yield, Qundef, &status);
	    ruby_stop(status);
	}
	return Qnil;

      case -1:
	rb_sys_fail("fork(2)");
	return Qnil;

      default:
	return PIDT2NUM(pid);
    }
}
#else
#define rb_f_fork rb_f_notimplement
#endif

/*
 *  call-seq:
 *     Process.exit!(status=false)
 *
 *  Exits the process immediately. No exit handlers are
 *  run. <em>status</em> is returned to the underlying system as the
 *  exit status.
 *
 *     Process.exit!(true)
 */

static VALUE
rb_f_exit_bang(int argc, VALUE *argv, VALUE obj)
{
    VALUE status;
    int istatus;

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
	switch (status) {
	  case Qtrue:
	    istatus = EXIT_SUCCESS;
	    break;
	  case Qfalse:
	    istatus = EXIT_FAILURE;
	    break;
	  default:
	    istatus = NUM2INT(status);
	    break;
	}
    }
    else {
	istatus = EXIT_FAILURE;
    }
    _exit(istatus);

    return Qnil;		/* not reached */
}

void
rb_exit(int status)
{
    if (GET_THREAD()->tag) {
	VALUE args[2];

	args[0] = INT2NUM(status);
	args[1] = rb_str_new2("exit");
	rb_exc_raise(rb_class_new_instance(2, args, rb_eSystemExit));
    }
    ruby_finalize();
    exit(status);
}


/*
 *  call-seq:
 *     exit(status=true)
 *     Kernel::exit(status=true)
 *     Process::exit(status=true)
 *
 *  Initiates the termination of the Ruby script by raising the
 *  <code>SystemExit</code> exception. This exception may be caught. The
 *  optional parameter is used to return a status code to the invoking
 *  environment.
 *  +true+ and +FALSE+ of _status_ means success and failure
 *  respectively.  The interpretation of other integer values are
 *  system dependent.
 *
 *     begin
 *       exit
 *       puts "never get here"
 *     rescue SystemExit
 *       puts "rescued a SystemExit exception"
 *     end
 *     puts "after begin block"
 *
 *  <em>produces:</em>
 *
 *     rescued a SystemExit exception
 *     after begin block
 *
 *  Just prior to termination, Ruby executes any <code>at_exit</code> functions
 *  (see Kernel::at_exit) and runs any object finalizers (see
 *  ObjectSpace::define_finalizer).
 *
 *     at_exit { puts "at_exit function" }
 *     ObjectSpace.define_finalizer("string",  proc { puts "in finalizer" })
 *     exit
 *
 *  <em>produces:</em>
 *
 *     at_exit function
 *     in finalizer
 */

VALUE
rb_f_exit(int argc, VALUE *argv)
{
    VALUE status;
    int istatus;

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
	switch (status) {
	  case Qtrue:
	    istatus = EXIT_SUCCESS;
	    break;
	  case Qfalse:
	    istatus = EXIT_FAILURE;
	    break;
	  default:
	    istatus = NUM2INT(status);
#if EXIT_SUCCESS != 0
	    if (istatus == 0)
		istatus = EXIT_SUCCESS;
#endif
	    break;
	}
    }
    else {
	istatus = EXIT_SUCCESS;
    }
    rb_exit(istatus);
    return Qnil;		/* not reached */
}


/*
 *  call-seq:
 *     abort
 *     Kernel::abort([msg])
 *     Process::abort([msg])
 *
 *  Terminate execution immediately, effectively by calling
 *  <code>Kernel.exit(false)</code>. If _msg_ is given, it is written
 *  to STDERR prior to terminating.
 */

VALUE
rb_f_abort(int argc, VALUE *argv)
{
    rb_secure(4);
    if (argc == 0) {
	if (!NIL_P(GET_THREAD()->errinfo)) {
	    ruby_error_print();
	}
	rb_exit(EXIT_FAILURE);
    }
    else {
	VALUE args[2];

	rb_scan_args(argc, argv, "1", &args[1]);
	StringValue(argv[0]);
	rb_io_puts(argc, argv, rb_stderr);
	args[0] = INT2NUM(EXIT_FAILURE);
	rb_exc_raise(rb_class_new_instance(2, args, rb_eSystemExit));
    }
    return Qnil;		/* not reached */
}

void
rb_syswait(rb_pid_t pid)
{
    static int overriding;
#ifdef SIGHUP
    RETSIGTYPE (*hfunc)(int) = 0;
#endif
#ifdef SIGQUIT
    RETSIGTYPE (*qfunc)(int) = 0;
#endif
    RETSIGTYPE (*ifunc)(int) = 0;
    int status;
    int i, hooked = FALSE;

    if (!overriding) {
#ifdef SIGHUP
	hfunc = signal(SIGHUP, SIG_IGN);
#endif
#ifdef SIGQUIT
	qfunc = signal(SIGQUIT, SIG_IGN);
#endif
	ifunc = signal(SIGINT, SIG_IGN);
	overriding = TRUE;
	hooked = TRUE;
    }

    do {
	i = rb_waitpid(pid, &status, 0);
    } while (i == -1 && errno == EINTR);

    if (hooked) {
#ifdef SIGHUP
	signal(SIGHUP, hfunc);
#endif
#ifdef SIGQUIT
	signal(SIGQUIT, qfunc);
#endif
	signal(SIGINT, ifunc);
	overriding = FALSE;
    }
}

static VALUE
rb_exec_arg_prepare(struct rb_exec_arg *earg, int argc, VALUE *argv, int default_close_others)
{
    VALUE prog = rb_exec_arg_init(argc, argv, TRUE, earg);
    if (NIL_P(rb_ary_entry(earg->options, EXEC_OPTION_CLOSE_OTHERS))) {
        VALUE v = default_close_others ? Qtrue : Qfalse;
        rb_exec_arg_addopt(earg, ID2SYM(rb_intern("close_others")), v);
    }
    rb_exec_arg_fixup(earg);
    return prog;
}

static rb_pid_t
rb_spawn_process(struct rb_exec_arg *earg, VALUE prog, char *errmsg, size_t errmsg_buflen)
{
    rb_pid_t pid;
#if !USE_SPAWNV
    int status;
#endif
#if !defined HAVE_FORK || USE_SPAWNV
    struct rb_exec_arg sarg;
    int argc;
    VALUE *argv;
#endif

#if defined HAVE_FORK && !USE_SPAWNV
    pid = rb_fork_err(&status, rb_exec_atfork, earg, earg->redirect_fds, errmsg, errmsg_buflen);
#else
    if (rb_run_exec_options_err(earg, &sarg, errmsg, errmsg_buflen) < 0) {
        return -1;
    }

    argc = earg->argc;
    argv = earg->argv;
    if (prog && argc) argv[0] = prog;
# if defined HAVE_SPAWNV
    if (!argc) {
	pid = proc_spawn(RSTRING_PTR(prog));
    }
    else {
	pid = proc_spawn_n(argc, argv, prog, earg->options);
    }
#  if defined(_WIN32)
    if (pid == -1)
	rb_last_status_set(0x7f << 8, 0);
#  endif
# else
    if (argc) prog = rb_ary_join(rb_ary_new4(argc, argv), rb_str_new2(" "));
    status = system(StringValuePtr(prog));
    rb_last_status_set((status & 0xff) << 8, 0);
# endif

    rb_run_exec_options_err(&sarg, NULL, errmsg, errmsg_buflen);
#endif
    return pid;
}

static rb_pid_t
rb_spawn_internal(int argc, VALUE *argv, int default_close_others,
                  char *errmsg, size_t errmsg_buflen)
{
    struct rb_exec_arg earg;
    VALUE prog = rb_exec_arg_prepare(&earg, argc, argv, default_close_others);
    return rb_spawn_process(&earg, prog, errmsg, errmsg_buflen);
}

rb_pid_t
rb_spawn_err(int argc, VALUE *argv, char *errmsg, size_t errmsg_buflen)
{
    return rb_spawn_internal(argc, argv, TRUE, errmsg, errmsg_buflen);
}

rb_pid_t
rb_spawn(int argc, VALUE *argv)
{
    return rb_spawn_internal(argc, argv, TRUE, NULL, 0);
}

/*
 *  call-seq:
 *     system([env,] command... [,options])    -> true, false or nil
 *
 *  Executes _command..._ in a subshell.
 *  _command..._ is one of following forms.
 *
 *    commandline                 : command line string which is passed to the standard shell
 *    cmdname, arg1, ...          : command name and one or more arguments (no shell)
 *    [cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
 *
 *  system returns +true+ if the command gives zero exit status,
 *  +false+ for non zero exit status.
 *  Returns +nil+ if command execution fails.
 *  An error status is available in <code>$?</code>.
 *  The arguments are processed in the same way as
 *  for <code>Kernel.spawn</code>.
 *
 *  The hash arguments, env and options, are same as
 *  <code>exec</code> and <code>spawn</code>.
 *  See <code>Kernel.spawn</code> for details.
 *
 *     system("echo *")
 *     system("echo", "*")
 *
 *  <em>produces:</em>
 *
 *     config.h main.rb
 *     *
 *
 *  See <code>Kernel.exec</code> for the standard shell.
 */

static VALUE
rb_f_system(int argc, VALUE *argv)
{
    rb_pid_t pid;
    int status;

#if defined(SIGCLD) && !defined(SIGCHLD)
# define SIGCHLD SIGCLD
#endif

#ifdef SIGCHLD
    RETSIGTYPE (*chfunc)(int);

    chfunc = signal(SIGCHLD, SIG_DFL);
#endif
    pid = rb_spawn_internal(argc, argv, FALSE, NULL, 0);
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    if (pid > 0) {
	rb_syswait(pid);
    }
#endif
#ifdef SIGCHLD
    signal(SIGCHLD, chfunc);
#endif
    if (pid < 0) {
	return Qnil;
    }
    status = PST2INT(rb_last_status_get());
    if (status == EXIT_SUCCESS) return Qtrue;
    return Qfalse;
}

/*
 *  call-seq:
 *     spawn([env,] command... [,options])     -> pid
 *     Process.spawn([env,] command... [,options])     -> pid
 *
 *  spawn executes specified command and return its pid.
 *
 *  This method doesn't wait for end of the command.
 *  The parent process should
 *  use <code>Process.wait</code> to collect
 *  the termination status of its child or
 *  use <code>Process.detach</code> to register
 *  disinterest in their status;
 *  otherwise, the operating system may accumulate zombie processes.
 *
 *  spawn has bunch of options to specify process attributes:
 *
 *    env: hash
 *      name => val : set the environment variable
 *      name => nil : unset the environment variable
 *    command...:
 *      commandline                 : command line string which is passed to the standard shell
 *      cmdname, arg1, ...          : command name and one or more arguments (no shell)
 *      [cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
 *    options: hash
 *      clearing environment variables:
 *        :unsetenv_others => true   : clear environment variables except specified by env
 *        :unsetenv_others => false  : don't clear (default)
 *      process group:
 *        :pgroup => true or 0 : make a new process group
 *        :pgroup => pgid      : join to specified process group
 *        :pgroup => nil       : don't change the process group (default)
 *      create new process group: Windows only
 *        :new_pgroup => true  : the new process is the root process of a new process group
 *        :new_pgroup => false : don't create a new process group (default)
 *      resource limit: resourcename is core, cpu, data, etc.  See Process.setrlimit.
 *        :rlimit_resourcename => limit
 *        :rlimit_resourcename => [cur_limit, max_limit]
 *      current directory:
 *        :chdir => str
 *      umask:
 *        :umask => int
 *      redirection:
 *        key:
 *          FD              : single file descriptor in child process
 *          [FD, FD, ...]   : multiple file descriptor in child process
 *        value:
 *          FD                        : redirect to the file descriptor in parent process
 *          string                    : redirect to file with open(string, "r" or "w")
 *          [string]                  : redirect to file with open(string, File::RDONLY)
 *          [string, open_mode]       : redirect to file with open(string, open_mode, 0644)
 *          [string, open_mode, perm] : redirect to file with open(string, open_mode, perm)
 *          [:child, FD]              : redirect to the redirected file descriptor
 *          :close                    : close the file descriptor in child process
 *        FD is one of follows
 *          :in     : the file descriptor 0 which is the standard input
 *          :out    : the file descriptor 1 which is the standard output
 *          :err    : the file descriptor 2 which is the standard error
 *          integer : the file descriptor of specified the integer
 *          io      : the file descriptor specified as io.fileno
 *      file descriptor inheritance: close non-redirected non-standard fds (3, 4, 5, ...) or not
 *        :close_others => false : inherit fds (default for system and exec)
 *        :close_others => true  : don't inherit (default for spawn and IO.popen)
 *
 *  If a hash is given as +env+, the environment is
 *  updated by +env+ before <code>exec(2)</code> in the child process.
 *  If a pair in +env+ has nil as the value, the variable is deleted.
 *
 *    # set FOO as BAR and unset BAZ.
 *    pid = spawn({"FOO"=>"BAR", "BAZ"=>nil}, command)
 *
 *  If a hash is given as +options+,
 *  it specifies
 *  process group,
 *  create new process group,
 *  resource limit,
 *  current directory,
 *  umask and
 *  redirects for the child process.
 *  Also, it can be specified to clear environment variables.
 *
 *  The <code>:unsetenv_others</code> key in +options+ specifies
 *  to clear environment variables, other than specified by +env+.
 *
 *    pid = spawn(command, :unsetenv_others=>true) # no environment variable
 *    pid = spawn({"FOO"=>"BAR"}, command, :unsetenv_others=>true) # FOO only
 *
 *  The <code>:pgroup</code> key in +options+ specifies a process group.
 *  The corresponding value should be true, zero or positive integer.
 *  true and zero means the process should be a process leader of a new
 *  process group.
 *  Other values specifies a process group to be belongs.
 *
 *    pid = spawn(command, :pgroup=>true) # process leader
 *    pid = spawn(command, :pgroup=>10) # belongs to the process group 10
 *
 *  The <code>:new_pgroup</code> key in +options+ specifies to pass
 *  +CREATE_NEW_PROCESS_GROUP+ flag to <code>CreateProcessW()</code> that is
 *  Windows API. This option is only for Windows.
 *  true means the new process is the root process of the new process group.
 *  The new process has CTRL+C disabled. This flag is necessary for
 *  <code>Process.kill(:SIGINT, pid)</code> on the subprocess.
 *  :new_pgroup is false by default.
 *
 *    pid = spawn(command, :new_pgroup=>true)  # new process group
 *    pid = spawn(command, :new_pgroup=>false) # same process group
 *
 *  The <code>:rlimit_</code><em>foo</em> key specifies a resource limit.
 *  <em>foo</em> should be one of resource types such as <code>core</code>.
 *  The corresponding value should be an integer or an array which have one or
 *  two integers: same as cur_limit and max_limit arguments for
 *  Process.setrlimit.
 *
 *    cur, max = Process.getrlimit(:CORE)
 *    pid = spawn(command, :rlimit_core=>[0,max]) # disable core temporary.
 *    pid = spawn(command, :rlimit_core=>max) # enable core dump
 *    pid = spawn(command, :rlimit_core=>0) # never dump core.
 *
 *  The <code>:chdir</code> key in +options+ specifies the current directory.
 *
 *    pid = spawn(command, :chdir=>"/var/tmp")
 *
 *  The <code>:umask</code> key in +options+ specifies the umask.
 *
 *    pid = spawn(command, :umask=>077)
 *
 *  The :in, :out, :err, a fixnum, an IO and an array key specifies a redirection.
 *  The redirection maps a file descriptor in the child process.
 *
 *  For example, stderr can be merged into stdout as follows:
 *
 *    pid = spawn(command, :err=>:out)
 *    pid = spawn(command, 2=>1)
 *    pid = spawn(command, STDERR=>:out)
 *    pid = spawn(command, STDERR=>STDOUT)
 *
 *  The hash keys specifies a file descriptor
 *  in the child process started by <code>spawn</code>.
 *  :err, 2 and STDERR specifies the standard error stream (stderr).
 *
 *  The hash values specifies a file descriptor
 *  in the parent process which invokes <code>spawn</code>.
 *  :out, 1 and STDOUT specifies the standard output stream (stdout).
 *
 *  In the above example,
 *  the standard output in the child process is not specified.
 *  So it is inherited from the parent process.
 *
 *  The standard input stream (stdin) can be specified by :in, 0 and STDIN.
 *
 *  A filename can be specified as a hash value.
 *
 *    pid = spawn(command, :in=>"/dev/null") # read mode
 *    pid = spawn(command, :out=>"/dev/null") # write mode
 *    pid = spawn(command, :err=>"log") # write mode
 *    pid = spawn(command, 3=>"/dev/null") # read mode
 *
 *  For stdout and stderr,
 *  it is opened in write mode.
 *  Otherwise read mode is used.
 *
 *  For specifying flags and permission of file creation explicitly,
 *  an array is used instead.
 *
 *    pid = spawn(command, :in=>["file"]) # read mode is assumed
 *    pid = spawn(command, :in=>["file", "r"])
 *    pid = spawn(command, :out=>["log", "w"]) # 0644 assumed
 *    pid = spawn(command, :out=>["log", "w", 0600])
 *    pid = spawn(command, :out=>["log", File::WRONLY|File::EXCL|File::CREAT, 0600])
 *
 *  The array specifies a filename, flags and permission.
 *  The flags can be a string or an integer.
 *  If the flags is omitted or nil, File::RDONLY is assumed.
 *  The permission should be an integer.
 *  If the permission is omitted or nil, 0644 is assumed.
 *
 *  If an array of IOs and integers are specified as a hash key,
 *  all the elements are redirected.
 *
 *    # stdout and stderr is redirected to log file.
 *    # The file "log" is opened just once.
 *    pid = spawn(command, [:out, :err]=>["log", "w"])
 *
 *  Another way to merge multiple file descriptors is [:child, fd].
 *  \[:child, fd] means the file descriptor in the child process.
 *  This is different from fd.
 *  For example, :err=>:out means redirecting child stderr to parent stdout.
 *  But :err=>[:child, :out] means redirecting child stderr to child stdout.
 *  They differs if stdout is redirected in the child process as follows.
 *
 *    # stdout and stderr is redirected to log file.
 *    # The file "log" is opened just once.
 *    pid = spawn(command, :out=>["log", "w"], :err=>[:child, :out])
 *
 *  \[:child, :out] can be used to merge stderr into stdout in IO.popen.
 *  In this case, IO.popen redirects stdout to a pipe in the child process
 *  and [:child, :out] refers the redirected stdout.
 *
 *    io = IO.popen(["sh", "-c", "echo out; echo err >&2", :err=>[:child, :out]])
 *    p io.read #=> "out\nerr\n"
 *
 *  spawn closes all non-standard unspecified descriptors by default.
 *  The "standard" descriptors are 0, 1 and 2.
 *  This behavior is specified by :close_others option.
 *  :close_others doesn't affect the standard descriptors which are
 *  closed only if :close is specified explicitly.
 *
 *    pid = spawn(command, :close_others=>true)  # close 3,4,5,... (default)
 *    pid = spawn(command, :close_others=>false) # don't close 3,4,5,...
 *
 *  :close_others is true by default for spawn and IO.popen.
 *
 *  So IO.pipe and spawn can be used as IO.popen.
 *
 *    # similar to r = IO.popen(command)
 *    r, w = IO.pipe
 *    pid = spawn(command, :out=>w)   # r, w is closed in the child process.
 *    w.close
 *
 *  :close is specified as a hash value to close a fd individually.
 *
 *    f = open(foo)
 *    system(command, f=>:close)        # don't inherit f.
 *
 *  If a file descriptor need to be inherited,
 *  io=>io can be used.
 *
 *    # valgrind has --log-fd option for log destination.
 *    # log_w=>log_w indicates log_w.fileno inherits to child process.
 *    log_r, log_w = IO.pipe
 *    pid = spawn("valgrind", "--log-fd=#{log_w.fileno}", "echo", "a", log_w=>log_w)
 *    log_w.close
 *    p log_r.read
 *
 *  It is also possible to exchange file descriptors.
 *
 *    pid = spawn(command, :out=>:err, :err=>:out)
 *
 *  The hash keys specify file descriptors in the child process.
 *  The hash values specifies file descriptors in the parent process.
 *  So the above specifies exchanging stdout and stderr.
 *  Internally, +spawn+ uses an extra file descriptor to resolve such cyclic
 *  file descriptor mapping.
 *
 *  See <code>Kernel.exec</code> for the standard shell.
 */

static VALUE
rb_f_spawn(int argc, VALUE *argv)
{
    rb_pid_t pid;
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };
    struct rb_exec_arg earg;

    pid = rb_spawn_process(&earg, rb_exec_arg_prepare(&earg, argc, argv, TRUE), errmsg, sizeof(errmsg));
    if (pid == -1) {
	const char *prog = errmsg;
	if (!prog[0] && !(prog = earg.prog) && earg.argc) {
	    prog = RSTRING_PTR(earg.argv[0]);
	}
	rb_sys_fail(prog);
    }
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    return PIDT2NUM(pid);
#else
    return Qnil;
#endif
}

/*
 *  call-seq:
 *     sleep([duration])    -> fixnum
 *
 *  Suspends the current thread for _duration_ seconds (which may be any number,
 *  including a +Float+ with fractional seconds). Returns the actual number of
 *  seconds slept (rounded), which may be less than that asked for if another
 *  thread calls <code>Thread#run</code>. Called without an argument, sleep()
 *  will sleep forever.
 *
 *     Time.new    #=> 2008-03-08 19:56:19 +0900
 *     sleep 1.2   #=> 1
 *     Time.new    #=> 2008-03-08 19:56:20 +0900
 *     sleep 1.9   #=> 2
 *     Time.new    #=> 2008-03-08 19:56:22 +0900
 */

static VALUE
rb_f_sleep(int argc, VALUE *argv)
{
    time_t beg, end;

    beg = time(0);
    if (argc == 0) {
	rb_thread_sleep_forever();
    }
    else if (argc == 1) {
	rb_thread_wait_for(rb_time_interval(argv[0]));
    }
    else {
	rb_raise(rb_eArgError, "wrong number of arguments (%d for 0..1)", argc);
    }

    end = time(0) - beg;

    return INT2FIX(end);
}


#if (defined(HAVE_GETPGRP) && defined(GETPGRP_VOID)) || defined(HAVE_GETPGID)
/*
 *  call-seq:
 *     Process.getpgrp   -> integer
 *
 *  Returns the process group ID for this process. Not available on
 *  all platforms.
 *
 *     Process.getpgid(0)   #=> 25527
 *     Process.getpgrp      #=> 25527
 */

static VALUE
proc_getpgrp(void)
{
    rb_pid_t pgrp;

    rb_secure(2);
#if defined(HAVE_GETPGRP) && defined(GETPGRP_VOID)
    pgrp = getpgrp();
    if (pgrp < 0) rb_sys_fail(0);
    return PIDT2NUM(pgrp);
#else /* defined(HAVE_GETPGID) */
    pgrp = getpgid(0);
    if (pgrp < 0) rb_sys_fail(0);
    return PIDT2NUM(pgrp);
#endif
}
#else
#define proc_getpgrp rb_f_notimplement
#endif


#if defined(HAVE_SETPGID) || (defined(HAVE_SETPGRP) && defined(SETPGRP_VOID))
/*
 *  call-seq:
 *     Process.setpgrp   -> 0
 *
 *  Equivalent to <code>setpgid(0,0)</code>. Not available on all
 *  platforms.
 */

static VALUE
proc_setpgrp(void)
{
    rb_secure(2);
  /* check for posix setpgid() first; this matches the posix */
  /* getpgrp() above.  It appears that configure will set SETPGRP_VOID */
  /* even though setpgrp(0,0) would be preferred. The posix call avoids */
  /* this confusion. */
#ifdef HAVE_SETPGID
    if (setpgid(0,0) < 0) rb_sys_fail(0);
#elif defined(HAVE_SETPGRP) && defined(SETPGRP_VOID)
    if (setpgrp() < 0) rb_sys_fail(0);
#endif
    return INT2FIX(0);
}
#else
#define proc_setpgrp rb_f_notimplement
#endif


#if defined(HAVE_GETPGID)
/*
 *  call-seq:
 *     Process.getpgid(pid)   -> integer
 *
 *  Returns the process group ID for the given process id. Not
 *  available on all platforms.
 *
 *     Process.getpgid(Process.ppid())   #=> 25527
 */

static VALUE
proc_getpgid(VALUE obj, VALUE pid)
{
    rb_pid_t i;

    rb_secure(2);
    i = getpgid(NUM2PIDT(pid));
    if (i < 0) rb_sys_fail(0);
    return PIDT2NUM(i);
}
#else
#define proc_getpgid rb_f_notimplement
#endif


#ifdef HAVE_SETPGID
/*
 *  call-seq:
 *     Process.setpgid(pid, integer)   -> 0
 *
 *  Sets the process group ID of _pid_ (0 indicates this
 *  process) to <em>integer</em>. Not available on all platforms.
 */

static VALUE
proc_setpgid(VALUE obj, VALUE pid, VALUE pgrp)
{
    rb_pid_t ipid, ipgrp;

    rb_secure(2);
    ipid = NUM2PIDT(pid);
    ipgrp = NUM2PIDT(pgrp);

    if (setpgid(ipid, ipgrp) < 0) rb_sys_fail(0);
    return INT2FIX(0);
}
#else
#define proc_setpgid rb_f_notimplement
#endif


#if defined(HAVE_SETSID) || (defined(HAVE_SETPGRP) && defined(TIOCNOTTY))
#if !defined(HAVE_SETSID)
static rb_pid_t ruby_setsid(void);
#define setsid() ruby_setsid()
#endif
/*
 *  call-seq:
 *     Process.setsid   -> fixnum
 *
 *  Establishes this process as a new session and process group
 *  leader, with no controlling tty. Returns the session id. Not
 *  available on all platforms.
 *
 *     Process.setsid   #=> 27422
 */

static VALUE
proc_setsid(void)
{
    rb_pid_t pid;

    rb_secure(2);
    pid = setsid();
    if (pid < 0) rb_sys_fail(0);
    return PIDT2NUM(pid);
}

#if !defined(HAVE_SETSID)
#define HAVE_SETSID 1
static rb_pid_t
ruby_setsid(void)
{
    rb_pid_t pid;
    int ret;

    pid = getpid();
#if defined(SETPGRP_VOID)
    ret = setpgrp();
    /* If `pid_t setpgrp(void)' is equivalent to setsid(),
       `ret' will be the same value as `pid', and following open() will fail.
       In Linux, `int setpgrp(void)' is equivalent to setpgid(0, 0). */
#else
    ret = setpgrp(0, pid);
#endif
    if (ret == -1) return -1;

    if ((fd = open("/dev/tty", O_RDWR)) >= 0) {
        rb_update_max_fd(fd);
	ioctl(fd, TIOCNOTTY, NULL);
	close(fd);
    }
    return pid;
}
#endif
#else
#define proc_setsid rb_f_notimplement
#endif


#ifdef HAVE_GETPRIORITY
/*
 *  call-seq:
 *     Process.getpriority(kind, integer)   -> fixnum
 *
 *  Gets the scheduling priority for specified process, process group,
 *  or user. <em>kind</em> indicates the kind of entity to find: one
 *  of <code>Process::PRIO_PGRP</code>,
 *  <code>Process::PRIO_USER</code>, or
 *  <code>Process::PRIO_PROCESS</code>. _integer_ is an id
 *  indicating the particular process, process group, or user (an id
 *  of 0 means _current_). Lower priorities are more favorable
 *  for scheduling. Not available on all platforms.
 *
 *     Process.getpriority(Process::PRIO_USER, 0)      #=> 19
 *     Process.getpriority(Process::PRIO_PROCESS, 0)   #=> 19
 */

static VALUE
proc_getpriority(VALUE obj, VALUE which, VALUE who)
{
    int prio, iwhich, iwho;

    rb_secure(2);
    iwhich = NUM2INT(which);
    iwho   = NUM2INT(who);

    errno = 0;
    prio = getpriority(iwhich, iwho);
    if (errno) rb_sys_fail(0);
    return INT2FIX(prio);
}
#else
#define proc_getpriority rb_f_notimplement
#endif


#ifdef HAVE_GETPRIORITY
/*
 *  call-seq:
 *     Process.setpriority(kind, integer, priority)   -> 0
 *
 *  See <code>Process#getpriority</code>.
 *
 *     Process.setpriority(Process::PRIO_USER, 0, 19)      #=> 0
 *     Process.setpriority(Process::PRIO_PROCESS, 0, 19)   #=> 0
 *     Process.getpriority(Process::PRIO_USER, 0)          #=> 19
 *     Process.getpriority(Process::PRIO_PROCESS, 0)       #=> 19
 */

static VALUE
proc_setpriority(VALUE obj, VALUE which, VALUE who, VALUE prio)
{
    int iwhich, iwho, iprio;

    rb_secure(2);
    iwhich = NUM2INT(which);
    iwho   = NUM2INT(who);
    iprio  = NUM2INT(prio);

    if (setpriority(iwhich, iwho, iprio) < 0)
	rb_sys_fail(0);
    return INT2FIX(0);
}
#else
#define proc_setpriority rb_f_notimplement
#endif

#if defined(HAVE_SETRLIMIT) && defined(NUM2RLIM)
static int
rlimit_resource_name2int(const char *name, int casetype)
{
    int resource;
    const char *p;
#define RESCHECK(r) \
    do { \
        if (STRCASECMP(name, #r) == 0) { \
            resource = RLIMIT_##r; \
            goto found; \
        } \
    } while (0)

    switch (TOUPPER(*name)) {
      case 'A':
#ifdef RLIMIT_AS
        RESCHECK(AS);
#endif
        break;

      case 'C':
#ifdef RLIMIT_CORE
        RESCHECK(CORE);
#endif
#ifdef RLIMIT_CPU
        RESCHECK(CPU);
#endif
        break;

      case 'D':
#ifdef RLIMIT_DATA
        RESCHECK(DATA);
#endif
        break;

      case 'F':
#ifdef RLIMIT_FSIZE
        RESCHECK(FSIZE);
#endif
        break;

      case 'M':
#ifdef RLIMIT_MEMLOCK
        RESCHECK(MEMLOCK);
#endif
#ifdef RLIMIT_MSGQUEUE
        RESCHECK(MSGQUEUE);
#endif
        break;

      case 'N':
#ifdef RLIMIT_NOFILE
        RESCHECK(NOFILE);
#endif
#ifdef RLIMIT_NPROC
        RESCHECK(NPROC);
#endif
#ifdef RLIMIT_NICE
        RESCHECK(NICE);
#endif
        break;

      case 'R':
#ifdef RLIMIT_RSS
        RESCHECK(RSS);
#endif
#ifdef RLIMIT_RTPRIO
        RESCHECK(RTPRIO);
#endif
#ifdef RLIMIT_RTTIME
        RESCHECK(RTTIME);
#endif
        break;

      case 'S':
#ifdef RLIMIT_STACK
        RESCHECK(STACK);
#endif
#ifdef RLIMIT_SBSIZE
        RESCHECK(SBSIZE);
#endif
#ifdef RLIMIT_SIGPENDING
        RESCHECK(SIGPENDING);
#endif
        break;
    }
    return -1;

  found:
    switch (casetype) {
      case 0:
        for (p = name; *p; p++)
            if (!ISUPPER(*p))
                return -1;
        break;

      case 1:
        for (p = name; *p; p++)
            if (!ISLOWER(*p))
                return -1;
        break;

      default:
        rb_bug("unexpected casetype");
    }
    return resource;
#undef RESCHECK
}

static int
rlimit_type_by_hname(const char *name)
{
    return rlimit_resource_name2int(name, 0);
}

static int
rlimit_type_by_lname(const char *name)
{
    return rlimit_resource_name2int(name, 1);
}

static int
rlimit_resource_type(VALUE rtype)
{
    const char *name;
    VALUE v;
    int r;

    switch (TYPE(rtype)) {
      case T_SYMBOL:
        name = rb_id2name(SYM2ID(rtype));
        break;

      default:
        v = rb_check_string_type(rtype);
        if (!NIL_P(v)) {
            rtype = v;
      case T_STRING:
            name = StringValueCStr(rtype);
            break;
        }
        /* fall through */

      case T_FIXNUM:
      case T_BIGNUM:
        return NUM2INT(rtype);
    }

    r = rlimit_type_by_hname(name);
    if (r != -1)
        return r;

    rb_raise(rb_eArgError, "invalid resource name: %s", name);
}

static rlim_t
rlimit_resource_value(VALUE rval)
{
    const char *name;
    VALUE v;

    switch (TYPE(rval)) {
      case T_SYMBOL:
        name = rb_id2name(SYM2ID(rval));
        break;

      default:
        v = rb_check_string_type(rval);
        if (!NIL_P(v)) {
            rval = v;
      case T_STRING:
            name = StringValueCStr(rval);
            break;
        }
        /* fall through */

      case T_FIXNUM:
      case T_BIGNUM:
        return NUM2RLIM(rval);
    }

#ifdef RLIM_INFINITY
    if (strcmp(name, "INFINITY") == 0) return RLIM_INFINITY;
#endif
#ifdef RLIM_SAVED_MAX
    if (strcmp(name, "SAVED_MAX") == 0) return RLIM_SAVED_MAX;
#endif
#ifdef RLIM_SAVED_CUR
    if (strcmp(name, "SAVED_CUR") == 0) return RLIM_SAVED_CUR;
#endif
    rb_raise(rb_eArgError, "invalid resource value: %s", name);
}
#endif

#if defined(HAVE_GETRLIMIT) && defined(RLIM2NUM)
/*
 *  call-seq:
 *     Process.getrlimit(resource)   -> [cur_limit, max_limit]
 *
 *  Gets the resource limit of the process.
 *  _cur_limit_ means current (soft) limit and
 *  _max_limit_ means maximum (hard) limit.
 *
 *  _resource_ indicates the kind of resource to limit.
 *  It is specified as a symbol such as <code>:CORE</code>,
 *  a string such as <code>"CORE"</code> or
 *  a constant such as <code>Process::RLIMIT_CORE</code>.
 *  See Process.setrlimit for details.
 *
 *  _cur_limit_ and _max_limit_ may be <code>Process::RLIM_INFINITY</code>,
 *  <code>Process::RLIM_SAVED_MAX</code> or
 *  <code>Process::RLIM_SAVED_CUR</code>.
 *  See Process.setrlimit and the system getrlimit(2) manual for details.
 */

static VALUE
proc_getrlimit(VALUE obj, VALUE resource)
{
    struct rlimit rlim;

    rb_secure(2);

    if (getrlimit(rlimit_resource_type(resource), &rlim) < 0) {
	rb_sys_fail("getrlimit");
    }
    return rb_assoc_new(RLIM2NUM(rlim.rlim_cur), RLIM2NUM(rlim.rlim_max));
}
#else
#define proc_getrlimit rb_f_notimplement
#endif

#if defined(HAVE_SETRLIMIT) && defined(NUM2RLIM)
/*
 *  call-seq:
 *     Process.setrlimit(resource, cur_limit, max_limit)        -> nil
 *     Process.setrlimit(resource, cur_limit)                   -> nil
 *
 *  Sets the resource limit of the process.
 *  _cur_limit_ means current (soft) limit and
 *  _max_limit_ means maximum (hard) limit.
 *
 *  If _max_limit_ is not given, _cur_limit_ is used.
 *
 *  _resource_ indicates the kind of resource to limit.
 *  It should be a symbol such as <code>:CORE</code>,
 *  a string such as <code>"CORE"</code> or
 *  a constant such as <code>Process::RLIMIT_CORE</code>.
 *  The available resources are OS dependent.
 *  Ruby may support following resources.
 *
 *  [AS] total available memory (bytes) (SUSv3, NetBSD, FreeBSD, OpenBSD but 4.4BSD-Lite)
 *  [CORE] core size (bytes) (SUSv3)
 *  [CPU] CPU time (seconds) (SUSv3)
 *  [DATA] data segment (bytes) (SUSv3)
 *  [FSIZE] file size (bytes) (SUSv3)
 *  [MEMLOCK] total size for mlock(2) (bytes) (4.4BSD, GNU/Linux)
 *  [MSGQUEUE] allocation for POSIX message queues (bytes) (GNU/Linux)
 *  [NICE] ceiling on process's nice(2) value (number) (GNU/Linux)
 *  [NOFILE] file descriptors (number) (SUSv3)
 *  [NPROC] number of processes for the user (number) (4.4BSD, GNU/Linux)
 *  [RSS] resident memory size (bytes) (4.2BSD, GNU/Linux)
 *  [RTPRIO] ceiling on the process's real-time priority (number) (GNU/Linux)
 *  [RTTIME] CPU time for real-time process (us) (GNU/Linux)
 *  [SBSIZE] all socket buffers (bytes) (NetBSD, FreeBSD)
 *  [SIGPENDING] number of queued signals allowed (signals) (GNU/Linux)
 *  [STACK] stack size (bytes) (SUSv3)
 *
 *  _cur_limit_ and _max_limit_ may be
 *  <code>:INFINITY</code>, <code>"INFINITY"</code> or
 *  <code>Process::RLIM_INFINITY</code>,
 *  which means that the resource is not limited.
 *  They may be <code>Process::RLIM_SAVED_MAX</code>,
 *  <code>Process::RLIM_SAVED_CUR</code> and
 *  corresponding symbols and strings too.
 *  See system setrlimit(2) manual for details.
 *
 *  The following example raises the soft limit of core size to
 *  the hard limit to try to make core dump possible.
 *
 *    Process.setrlimit(:CORE, Process.getrlimit(:CORE)[1])
 *
 */

static VALUE
proc_setrlimit(int argc, VALUE *argv, VALUE obj)
{
    VALUE resource, rlim_cur, rlim_max;
    struct rlimit rlim;

    rb_secure(2);

    rb_scan_args(argc, argv, "21", &resource, &rlim_cur, &rlim_max);
    if (rlim_max == Qnil)
        rlim_max = rlim_cur;

    rlim.rlim_cur = rlimit_resource_value(rlim_cur);
    rlim.rlim_max = rlimit_resource_value(rlim_max);

    if (setrlimit(rlimit_resource_type(resource), &rlim) < 0) {
	rb_sys_fail("setrlimit");
    }
    return Qnil;
}
#else
#define proc_setrlimit rb_f_notimplement
#endif

static int under_uid_switch = 0;
static void
check_uid_switch(void)
{
    rb_secure(2);
    if (under_uid_switch) {
	rb_raise(rb_eRuntimeError, "can't handle UID while evaluating block given to Process::UID.switch method");
    }
}

static int under_gid_switch = 0;
static void
check_gid_switch(void)
{
    rb_secure(2);
    if (under_gid_switch) {
	rb_raise(rb_eRuntimeError, "can't handle GID while evaluating block given to Process::UID.switch method");
    }
}


/*********************************************************************
 * Document-class: Process::Sys
 *
 *  The <code>Process::Sys</code> module contains UID and GID
 *  functions which provide direct bindings to the system calls of the
 *  same names instead of the more-portable versions of the same
 *  functionality found in the <code>Process</code>,
 *  <code>Process::UID</code>, and <code>Process::GID</code> modules.
 */


#if defined HAVE_SETUID
/*
 *  call-seq:
 *     Process::Sys.setuid(integer)   -> nil
 *
 *  Set the user ID of the current process to _integer_. Not
 *  available on all platforms.
 *
 */

static VALUE
p_sys_setuid(VALUE obj, VALUE id)
{
    check_uid_switch();
    if (setuid(NUM2UIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setuid rb_f_notimplement
#endif


#if defined HAVE_SETRUID
/*
 *  call-seq:
 *     Process::Sys.setruid(integer)   -> nil
 *
 *  Set the real user ID of the calling process to _integer_.
 *  Not available on all platforms.
 *
 */

static VALUE
p_sys_setruid(VALUE obj, VALUE id)
{
    check_uid_switch();
    if (setruid(NUM2UIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setruid rb_f_notimplement
#endif


#if defined HAVE_SETEUID
/*
 *  call-seq:
 *     Process::Sys.seteuid(integer)   -> nil
 *
 *  Set the effective user ID of the calling process to
 *  _integer_.  Not available on all platforms.
 *
 */

static VALUE
p_sys_seteuid(VALUE obj, VALUE id)
{
    check_uid_switch();
    if (seteuid(NUM2UIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_seteuid rb_f_notimplement
#endif


#if defined HAVE_SETREUID
/*
 *  call-seq:
 *     Process::Sys.setreuid(rid, eid)   -> nil
 *
 *  Sets the (integer) real and/or effective user IDs of the current
 *  process to _rid_ and _eid_, respectively. A value of
 *  <code>-1</code> for either means to leave that ID unchanged. Not
 *  available on all platforms.
 *
 */

static VALUE
p_sys_setreuid(VALUE obj, VALUE rid, VALUE eid)
{
    check_uid_switch();
    if (setreuid(NUM2UIDT(rid),NUM2UIDT(eid)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setreuid rb_f_notimplement
#endif


#if defined HAVE_SETRESUID
/*
 *  call-seq:
 *     Process::Sys.setresuid(rid, eid, sid)   -> nil
 *
 *  Sets the (integer) real, effective, and saved user IDs of the
 *  current process to _rid_, _eid_, and _sid_ respectively. A
 *  value of <code>-1</code> for any value means to
 *  leave that ID unchanged. Not available on all platforms.
 *
 */

static VALUE
p_sys_setresuid(VALUE obj, VALUE rid, VALUE eid, VALUE sid)
{
    check_uid_switch();
    if (setresuid(NUM2UIDT(rid),NUM2UIDT(eid),NUM2UIDT(sid)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setresuid rb_f_notimplement
#endif


/*
 *  call-seq:
 *     Process.uid           -> fixnum
 *     Process::UID.rid      -> fixnum
 *     Process::Sys.getuid   -> fixnum
 *
 *  Returns the (real) user ID of this process.
 *
 *     Process.uid   #=> 501
 */

static VALUE
proc_getuid(VALUE obj)
{
    rb_uid_t uid = getuid();
    return UIDT2NUM(uid);
}


#if defined(HAVE_SETRESUID) || defined(HAVE_SETREUID) || defined(HAVE_SETRUID) || defined(HAVE_SETUID)
/*
 *  call-seq:
 *     Process.uid= integer   -> numeric
 *
 *  Sets the (integer) user ID for this process. Not available on all
 *  platforms.
 */

static VALUE
proc_setuid(VALUE obj, VALUE id)
{
    rb_uid_t uid;

    check_uid_switch();

    uid = NUM2UIDT(id);
#if defined(HAVE_SETRESUID)
    if (setresuid(uid, -1, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREUID
    if (setreuid(uid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETRUID
    if (setruid(uid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETUID
    {
	if (geteuid() == uid) {
	    if (setuid(uid) < 0) rb_sys_fail(0);
	}
	else {
	    rb_notimplement();
	}
    }
#endif
    return id;
}
#else
#define proc_setuid rb_f_notimplement
#endif


/********************************************************************
 *
 * Document-class: Process::UID
 *
 *  The <code>Process::UID</code> module contains a collection of
 *  module functions which can be used to portably get, set, and
 *  switch the current process's real, effective, and saved user IDs.
 *
 */

static rb_uid_t SAVED_USER_ID = -1;

#ifdef BROKEN_SETREUID
int
setreuid(rb_uid_t ruid, rb_uid_t euid)
{
    if (ruid != (rb_uid_t)-1 && ruid != getuid()) {
	if (euid == (rb_uid_t)-1) euid = geteuid();
	if (setuid(ruid) < 0) return -1;
    }
    if (euid != (rb_uid_t)-1 && euid != geteuid()) {
	if (seteuid(euid) < 0) return -1;
    }
    return 0;
}
#endif

/*
 *  call-seq:
 *     Process::UID.change_privilege(integer)   -> fixnum
 *
 *  Change the current process's real and effective user ID to that
 *  specified by _integer_. Returns the new user ID. Not
 *  available on all platforms.
 *
 *     [Process.uid, Process.euid]          #=> [0, 0]
 *     Process::UID.change_privilege(31)    #=> 31
 *     [Process.uid, Process.euid]          #=> [31, 31]
 */

static VALUE
p_uid_change_privilege(VALUE obj, VALUE id)
{
    rb_uid_t uid;

    check_uid_switch();

    uid = NUM2UIDT(id);

    if (geteuid() == 0) { /* root-user */
#if defined(HAVE_SETRESUID)
	if (setresuid(uid, uid, uid) < 0) rb_sys_fail(0);
	SAVED_USER_ID = uid;
#elif defined(HAVE_SETUID)
	if (setuid(uid) < 0) rb_sys_fail(0);
	SAVED_USER_ID = uid;
#elif defined(HAVE_SETREUID) && !defined(OBSOLETE_SETREUID)
	if (getuid() == uid) {
	    if (SAVED_USER_ID == uid) {
		if (setreuid(-1, uid) < 0) rb_sys_fail(0);
	    } else {
		if (uid == 0) { /* (r,e,s) == (root, root, x) */
		    if (setreuid(-1, SAVED_USER_ID) < 0) rb_sys_fail(0);
		    if (setreuid(SAVED_USER_ID, 0) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = 0; /* (r,e,s) == (x, root, root) */
		    if (setreuid(uid, uid) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = uid;
		} else {
		    if (setreuid(0, -1) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = 0;
		    if (setreuid(uid, uid) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = uid;
		}
	    }
	} else {
	    if (setreuid(uid, uid) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	}
#elif defined(HAVE_SETRUID) && defined(HAVE_SETEUID)
	if (getuid() == uid) {
	    if (SAVED_USER_ID == uid) {
		if (seteuid(uid) < 0) rb_sys_fail(0);
	    } else {
		if (uid == 0) {
		    if (setruid(SAVED_USER_ID) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = 0;
		    if (setruid(0) < 0) rb_sys_fail(0);
		} else {
		    if (setruid(0) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = 0;
		    if (seteuid(uid) < 0) rb_sys_fail(0);
		    if (setruid(uid) < 0) rb_sys_fail(0);
		    SAVED_USER_ID = uid;
		}
	    }
	} else {
	    if (seteuid(uid) < 0) rb_sys_fail(0);
	    if (setruid(uid) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	}
#else
	rb_notimplement();
#endif
    } else { /* unprivileged user */
#if defined(HAVE_SETRESUID)
	if (setresuid((getuid() == uid)? (rb_uid_t)-1: uid,
		      (geteuid() == uid)? (rb_uid_t)-1: uid,
		      (SAVED_USER_ID == uid)? (rb_uid_t)-1: uid) < 0) rb_sys_fail(0);
	SAVED_USER_ID = uid;
#elif defined(HAVE_SETREUID) && !defined(OBSOLETE_SETREUID)
	if (SAVED_USER_ID == uid) {
	    if (setreuid((getuid() == uid)? (rb_uid_t)-1: uid,
			 (geteuid() == uid)? (rb_uid_t)-1: uid) < 0)
		rb_sys_fail(0);
	} else if (getuid() != uid) {
	    if (setreuid(uid, (geteuid() == uid)? (rb_uid_t)-1: uid) < 0)
		rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	} else if (/* getuid() == uid && */ geteuid() != uid) {
	    if (setreuid(geteuid(), uid) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	    if (setreuid(uid, -1) < 0) rb_sys_fail(0);
	} else { /* getuid() == uid && geteuid() == uid */
	    if (setreuid(-1, SAVED_USER_ID) < 0) rb_sys_fail(0);
	    if (setreuid(SAVED_USER_ID, uid) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	    if (setreuid(uid, -1) < 0) rb_sys_fail(0);
	}
#elif defined(HAVE_SETRUID) && defined(HAVE_SETEUID)
	if (SAVED_USER_ID == uid) {
	    if (geteuid() != uid && seteuid(uid) < 0) rb_sys_fail(0);
	    if (getuid() != uid && setruid(uid) < 0) rb_sys_fail(0);
	} else if (/* SAVED_USER_ID != uid && */ geteuid() == uid) {
	    if (getuid() != uid) {
		if (setruid(uid) < 0) rb_sys_fail(0);
		SAVED_USER_ID = uid;
	    } else {
		if (setruid(SAVED_USER_ID) < 0) rb_sys_fail(0);
		SAVED_USER_ID = uid;
		if (setruid(uid) < 0) rb_sys_fail(0);
	    }
	} else if (/* geteuid() != uid && */ getuid() == uid) {
	    if (seteuid(uid) < 0) rb_sys_fail(0);
	    if (setruid(SAVED_USER_ID) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	    if (setruid(uid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_44BSD_SETUID
	if (getuid() == uid) {
	    /* (r,e,s)==(uid,?,?) ==> (uid,uid,uid) */
	    if (setuid(uid) < 0) rb_sys_fail(0);
	    SAVED_USER_ID = uid;
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_SETEUID
	if (getuid() == uid && SAVED_USER_ID == uid) {
	    if (seteuid(uid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_SETUID
	if (getuid() == uid && SAVED_USER_ID == uid) {
	    if (setuid(uid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#else
	rb_notimplement();
#endif
    }
    return id;
}



#if defined HAVE_SETGID
/*
 *  call-seq:
 *     Process::Sys.setgid(integer)   -> nil
 *
 *  Set the group ID of the current process to _integer_. Not
 *  available on all platforms.
 *
 */

static VALUE
p_sys_setgid(VALUE obj, VALUE id)
{
    check_gid_switch();
    if (setgid(NUM2GIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setgid rb_f_notimplement
#endif


#if defined HAVE_SETRGID
/*
 *  call-seq:
 *     Process::Sys.setrgid(integer)   -> nil
 *
 *  Set the real group ID of the calling process to _integer_.
 *  Not available on all platforms.
 *
 */

static VALUE
p_sys_setrgid(VALUE obj, VALUE id)
{
    check_gid_switch();
    if (setrgid(NUM2GIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setrgid rb_f_notimplement
#endif


#if defined HAVE_SETEGID
/*
 *  call-seq:
 *     Process::Sys.setegid(integer)   -> nil
 *
 *  Set the effective group ID of the calling process to
 *  _integer_.  Not available on all platforms.
 *
 */

static VALUE
p_sys_setegid(VALUE obj, VALUE id)
{
    check_gid_switch();
    if (setegid(NUM2GIDT(id)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setegid rb_f_notimplement
#endif


#if defined HAVE_SETREGID
/*
 *  call-seq:
 *     Process::Sys.setregid(rid, eid)   -> nil
 *
 *  Sets the (integer) real and/or effective group IDs of the current
 *  process to <em>rid</em> and <em>eid</em>, respectively. A value of
 *  <code>-1</code> for either means to leave that ID unchanged. Not
 *  available on all platforms.
 *
 */

static VALUE
p_sys_setregid(VALUE obj, VALUE rid, VALUE eid)
{
    check_gid_switch();
    if (setregid(NUM2GIDT(rid),NUM2GIDT(eid)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setregid rb_f_notimplement
#endif

#if defined HAVE_SETRESGID
/*
 *  call-seq:
 *     Process::Sys.setresgid(rid, eid, sid)   -> nil
 *
 *  Sets the (integer) real, effective, and saved user IDs of the
 *  current process to <em>rid</em>, <em>eid</em>, and <em>sid</em>
 *  respectively. A value of <code>-1</code> for any value means to
 *  leave that ID unchanged. Not available on all platforms.
 *
 */

static VALUE
p_sys_setresgid(VALUE obj, VALUE rid, VALUE eid, VALUE sid)
{
    check_gid_switch();
    if (setresgid(NUM2GIDT(rid),NUM2GIDT(eid),NUM2GIDT(sid)) != 0) rb_sys_fail(0);
    return Qnil;
}
#else
#define p_sys_setresgid rb_f_notimplement
#endif


#if defined HAVE_ISSETUGID
/*
 *  call-seq:
 *     Process::Sys.issetugid   -> true or false
 *
 *  Returns +true+ if the process was created as a result
 *  of an execve(2) system call which had either of the setuid or
 *  setgid bits set (and extra privileges were given as a result) or
 *  if it has changed any of its real, effective or saved user or
 *  group IDs since it began execution.
 *
 */

static VALUE
p_sys_issetugid(VALUE obj)
{
    rb_secure(2);
    if (issetugid()) {
	return Qtrue;
    } else {
	return Qfalse;
    }
}
#else
#define p_sys_issetugid rb_f_notimplement
#endif


/*
 *  call-seq:
 *     Process.gid           -> fixnum
 *     Process::GID.rid      -> fixnum
 *     Process::Sys.getgid   -> fixnum
 *
 *  Returns the (real) group ID for this process.
 *
 *     Process.gid   #=> 500
 */

static VALUE
proc_getgid(VALUE obj)
{
    rb_gid_t gid = getgid();
    return GIDT2NUM(gid);
}


#if defined(HAVE_SETRESGID) || defined(HAVE_SETREGID) || defined(HAVE_SETRGID) || defined(HAVE_SETGID)
/*
 *  call-seq:
 *     Process.gid= fixnum   -> fixnum
 *
 *  Sets the group ID for this process.
 */

static VALUE
proc_setgid(VALUE obj, VALUE id)
{
    rb_gid_t gid;

    check_gid_switch();

    gid = NUM2GIDT(id);
#if defined(HAVE_SETRESGID)
    if (setresgid(gid, -1, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREGID
    if (setregid(gid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETRGID
    if (setrgid(gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETGID
    {
	if (getegid() == gid) {
	    if (setgid(gid) < 0) rb_sys_fail(0);
	}
	else {
	    rb_notimplement();
	}
    }
#endif
    return GIDT2NUM(gid);
}
#else
#define proc_setgid rb_f_notimplement
#endif


#if defined(HAVE_SETGROUPS) || defined(HAVE_GETGROUPS)
/*
 * Maximum supplementary groups are platform dependent.
 * FWIW, 65536 is enough big for our supported OSs.
 *
 * OS Name			max groups
 * -----------------------------------------------
 * Linux Kernel >= 2.6.3	65536
 * Linux Kernel < 2.6.3		   32
 * IBM AIX 5.2			   64
 * IBM AIX 5.3 ... 6.1		  128
 * IBM AIX 7.1			  128 (can be configured to be up to 2048)
 * OpenBSD, NetBSD		   16
 * FreeBSD < 8.0		   16
 * FreeBSD >=8.0		 1023
 * Darwin (Mac OS X)		   16
 * Sun Solaris 7,8,9,10		   16
 * Sun Solaris 11 / OpenSolaris	 1024
 * HP-UX			   20
 * Windows			 1015
 */
#define RB_MAX_GROUPS (65536)
static int _maxgroups = -1;
static int get_sc_ngroups_max(void)
{
#ifdef _SC_NGROUPS_MAX
    return (int)sysconf(_SC_NGROUPS_MAX);
#elif defined(NGROUPS_MAX)
    return (int)NGROUPS_MAX;
#else
    return -1;
#endif
}
static int maxgroups(void)
{
    if (_maxgroups < 0) {
	_maxgroups = get_sc_ngroups_max();
	if (_maxgroups < 0)
	    _maxgroups = RB_MAX_GROUPS;
    }

    return _maxgroups;
}
#endif



#ifdef HAVE_GETGROUPS
/*
 *  call-seq:
 *     Process.groups   -> array
 *
 *  Get an <code>Array</code> of the gids of groups in the
 *  supplemental group access list for this process.
 *
 *     Process.groups   #=> [27, 6, 10, 11]
 *
 */

static VALUE
proc_getgroups(VALUE obj)
{
    VALUE ary;
    int i, ngroups;
    rb_gid_t *groups;

    ngroups = getgroups(0, NULL);
    if (ngroups == -1)
	rb_sys_fail(0);

    groups = ALLOCA_N(rb_gid_t, ngroups);

    ngroups = getgroups(ngroups, groups);
    if (ngroups == -1)
	rb_sys_fail(0);

    ary = rb_ary_new();
    for (i = 0; i < ngroups; i++)
	rb_ary_push(ary, GIDT2NUM(groups[i]));

    return ary;
}
#else
#define proc_getgroups rb_f_notimplement
#endif


#ifdef HAVE_SETGROUPS
/*
 *  call-seq:
 *     Process.groups= array   -> array
 *
 *  Set the supplemental group access list to the given
 *  <code>Array</code> of group IDs.
 *
 *     Process.groups   #=> [0, 1, 2, 3, 4, 6, 10, 11, 20, 26, 27]
 *     Process.groups = [27, 6, 10, 11]   #=> [27, 6, 10, 11]
 *     Process.groups   #=> [27, 6, 10, 11]
 *
 */

static VALUE
proc_setgroups(VALUE obj, VALUE ary)
{
    int ngroups, i;
    rb_gid_t *groups;
#ifdef HAVE_GETGRNAM_R
    long getgr_buf_len = sysconf(_SC_GETGR_R_SIZE_MAX);
    char* getgr_buf;

    if (getgr_buf_len < 0)
	getgr_buf_len = 4096;
    getgr_buf = ALLOCA_N(char, getgr_buf_len);
#endif

    Check_Type(ary, T_ARRAY);

    ngroups = RARRAY_LENINT(ary);
    if (ngroups > maxgroups())
	rb_raise(rb_eArgError, "too many groups, %d max", maxgroups());

    groups = ALLOCA_N(rb_gid_t, ngroups);

    for (i = 0; i < ngroups; i++) {
	VALUE g = RARRAY_PTR(ary)[i];

	if (FIXNUM_P(g)) {
	    groups[i] = NUM2GIDT(g);
	}
	else {
	    VALUE tmp = rb_check_string_type(g);
	    struct group grp;
	    struct group *p;
	    int ret;

	    if (NIL_P(tmp)) {
		groups[i] = NUM2GIDT(g);
	    }
	    else {
		const char *grpname = StringValueCStr(tmp);

#ifdef HAVE_GETGRNAM_R
		ret = getgrnam_r(grpname, &grp, getgr_buf, getgr_buf_len, &p);
		if (ret)
		    rb_sys_fail("getgrnam_r");
#else
		p = getgrnam(grpname);
#endif
		if (p == NULL) {
		    rb_raise(rb_eArgError,
			     "can't find group for %s", RSTRING_PTR(tmp));
		}
		groups[i] = p->gr_gid;
	    }
	}
    }

    if (setgroups(ngroups, groups) == -1) /* ngroups <= maxgroups */
	rb_sys_fail(0);

    return proc_getgroups(obj);
}
#else
#define proc_setgroups rb_f_notimplement
#endif


#ifdef HAVE_INITGROUPS
/*
 *  call-seq:
 *     Process.initgroups(username, gid)   -> array
 *
 *  Initializes the supplemental group access list by reading the
 *  system group database and using all groups of which the given user
 *  is a member. The group with the specified <em>gid</em> is also
 *  added to the list. Returns the resulting <code>Array</code> of the
 *  gids of all the groups in the supplementary group access list. Not
 *  available on all platforms.
 *
 *     Process.groups   #=> [0, 1, 2, 3, 4, 6, 10, 11, 20, 26, 27]
 *     Process.initgroups( "mgranger", 30 )   #=> [30, 6, 10, 11]
 *     Process.groups   #=> [30, 6, 10, 11]
 *
 */

static VALUE
proc_initgroups(VALUE obj, VALUE uname, VALUE base_grp)
{
    if (initgroups(StringValuePtr(uname), NUM2GIDT(base_grp)) != 0) {
	rb_sys_fail(0);
    }
    return proc_getgroups(obj);
}
#else
#define proc_initgroups rb_f_notimplement
#endif

#if defined(_SC_NGROUPS_MAX) || defined(NGROUPS_MAX)
/*
 *  call-seq:
 *     Process.maxgroups   -> fixnum
 *
 *  Returns the maximum number of gids allowed in the supplemental
 *  group access list.
 *
 *     Process.maxgroups   #=> 32
 */

static VALUE
proc_getmaxgroups(VALUE obj)
{
    return INT2FIX(maxgroups());
}
#else
#define proc_getmaxgroups rb_f_notimplement
#endif

#ifdef HAVE_SETGROUPS
/*
 *  call-seq:
 *     Process.maxgroups= fixnum   -> fixnum
 *
 *  Sets the maximum number of gids allowed in the supplemental group
 *  access list.
 */

static VALUE
proc_setmaxgroups(VALUE obj, VALUE val)
{
    int ngroups = FIX2INT(val);
    int ngroups_max = get_sc_ngroups_max();

    if (ngroups <= 0)
	rb_raise(rb_eArgError, "maxgroups %d shold be positive", ngroups);

    if (ngroups > RB_MAX_GROUPS)
	ngroups = RB_MAX_GROUPS;

    if (ngroups_max > 0 && ngroups > ngroups_max)
	ngroups = ngroups_max;

    _maxgroups = ngroups;

    return INT2FIX(_maxgroups);
}
#else
#define proc_setmaxgroups rb_f_notimplement
#endif

#if defined(HAVE_DAEMON) || (defined(HAVE_FORK) && defined(HAVE_SETSID))
static int rb_daemon(int nochdir, int noclose);

/*
 *  call-seq:
 *     Process.daemon()                        -> 0
 *     Process.daemon(nochdir=nil,noclose=nil) -> 0
 *
 *  Detach the process from controlling terminal and run in
 *  the background as system daemon.  Unless the argument
 *  nochdir is true (i.e. non false), it changes the current
 *  working directory to the root ("/"). Unless the argument
 *  noclose is true, daemon() will redirect standard input,
 *  standard output and standard error to /dev/null.
 *  Return zero on success, or raise one of Errno::*.
 */

static VALUE
proc_daemon(int argc, VALUE *argv)
{
    VALUE nochdir, noclose;
    int n;

    rb_secure(2);
    rb_scan_args(argc, argv, "02", &nochdir, &noclose);

    prefork();
    n = rb_daemon(RTEST(nochdir), RTEST(noclose));
    if (n < 0) rb_sys_fail("daemon");
    return INT2FIX(n);
}

static int
rb_daemon(int nochdir, int noclose)
{
    int err = 0;
#ifdef HAVE_DAEMON
    before_fork();
    err = daemon(nochdir, noclose);
    after_fork();
    rb_thread_atfork();
#else
    int n;

#define fork_daemon() \
    switch (rb_fork(0, 0, 0, Qnil)) { \
      case -1: return -1; \
      case 0:  rb_thread_atfork(); break; \
      default: _exit(EXIT_SUCCESS); \
    }

    fork_daemon();

    if (setsid() < 0) return -1;

    /* must not be process-leader */
    fork_daemon();

    if (!nochdir)
	err = chdir("/");

    if (!noclose && (n = open("/dev/null", O_RDWR, 0)) != -1) {
        rb_update_max_fd(n);
	(void)dup2(n, 0);
	(void)dup2(n, 1);
	(void)dup2(n, 2);
	if (n > 2)
	    (void)close (n);
    }
#endif
    return err;
}
#else
#define proc_daemon rb_f_notimplement
#endif

/********************************************************************
 *
 * Document-class: Process::GID
 *
 *  The <code>Process::GID</code> module contains a collection of
 *  module functions which can be used to portably get, set, and
 *  switch the current process's real, effective, and saved group IDs.
 *
 */

static rb_gid_t SAVED_GROUP_ID = -1;

#ifdef BROKEN_SETREGID
int
setregid(rb_gid_t rgid, rb_gid_t egid)
{
    if (rgid != (rb_gid_t)-1 && rgid != getgid()) {
	if (egid == (rb_gid_t)-1) egid = getegid();
	if (setgid(rgid) < 0) return -1;
    }
    if (egid != (rb_gid_t)-1 && egid != getegid()) {
	if (setegid(egid) < 0) return -1;
    }
    return 0;
}
#endif

/*
 *  call-seq:
 *     Process::GID.change_privilege(integer)   -> fixnum
 *
 *  Change the current process's real and effective group ID to that
 *  specified by _integer_. Returns the new group ID. Not
 *  available on all platforms.
 *
 *     [Process.gid, Process.egid]          #=> [0, 0]
 *     Process::GID.change_privilege(33)    #=> 33
 *     [Process.gid, Process.egid]          #=> [33, 33]
 */

static VALUE
p_gid_change_privilege(VALUE obj, VALUE id)
{
    rb_gid_t gid;

    check_gid_switch();

    gid = NUM2GIDT(id);

    if (geteuid() == 0) { /* root-user */
#if defined(HAVE_SETRESGID)
	if (setresgid(gid, gid, gid) < 0) rb_sys_fail(0);
	SAVED_GROUP_ID = gid;
#elif defined HAVE_SETGID
	if (setgid(gid) < 0) rb_sys_fail(0);
	SAVED_GROUP_ID = gid;
#elif defined(HAVE_SETREGID) && !defined(OBSOLETE_SETREGID)
	if (getgid() == gid) {
	    if (SAVED_GROUP_ID == gid) {
		if (setregid(-1, gid) < 0) rb_sys_fail(0);
	    } else {
		if (gid == 0) { /* (r,e,s) == (root, y, x) */
		    if (setregid(-1, SAVED_GROUP_ID) < 0) rb_sys_fail(0);
		    if (setregid(SAVED_GROUP_ID, 0) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = 0; /* (r,e,s) == (x, root, root) */
		    if (setregid(gid, gid) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = gid;
		} else { /* (r,e,s) == (z, y, x) */
		    if (setregid(0, 0) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = 0;
		    if (setregid(gid, gid) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = gid;
		}
	    }
	} else {
	    if (setregid(gid, gid) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	}
#elif defined(HAVE_SETRGID) && defined (HAVE_SETEGID)
	if (getgid() == gid) {
	    if (SAVED_GROUP_ID == gid) {
		if (setegid(gid) < 0) rb_sys_fail(0);
	    } else {
		if (gid == 0) {
		    if (setegid(gid) < 0) rb_sys_fail(0);
		    if (setrgid(SAVED_GROUP_ID) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = 0;
		    if (setrgid(0) < 0) rb_sys_fail(0);
		} else {
		    if (setrgid(0) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = 0;
		    if (setegid(gid) < 0) rb_sys_fail(0);
		    if (setrgid(gid) < 0) rb_sys_fail(0);
		    SAVED_GROUP_ID = gid;
		}
	    }
	} else {
	    if (setegid(gid) < 0) rb_sys_fail(0);
	    if (setrgid(gid) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	}
#else
	rb_notimplement();
#endif
    } else { /* unprivileged user */
#if defined(HAVE_SETRESGID)
	if (setresgid((getgid() == gid)? (rb_gid_t)-1: gid,
		      (getegid() == gid)? (rb_gid_t)-1: gid,
		      (SAVED_GROUP_ID == gid)? (rb_gid_t)-1: gid) < 0) rb_sys_fail(0);
	SAVED_GROUP_ID = gid;
#elif defined(HAVE_SETREGID) && !defined(OBSOLETE_SETREGID)
	if (SAVED_GROUP_ID == gid) {
	    if (setregid((getgid() == gid)? (rb_uid_t)-1: gid,
			 (getegid() == gid)? (rb_uid_t)-1: gid) < 0)
		rb_sys_fail(0);
	} else if (getgid() != gid) {
	    if (setregid(gid, (getegid() == gid)? (rb_uid_t)-1: gid) < 0)
		rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	} else if (/* getgid() == gid && */ getegid() != gid) {
	    if (setregid(getegid(), gid) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	    if (setregid(gid, -1) < 0) rb_sys_fail(0);
	} else { /* getgid() == gid && getegid() == gid */
	    if (setregid(-1, SAVED_GROUP_ID) < 0) rb_sys_fail(0);
	    if (setregid(SAVED_GROUP_ID, gid) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	    if (setregid(gid, -1) < 0) rb_sys_fail(0);
	}
#elif defined(HAVE_SETRGID) && defined(HAVE_SETEGID)
	if (SAVED_GROUP_ID == gid) {
	    if (getegid() != gid && setegid(gid) < 0) rb_sys_fail(0);
	    if (getgid() != gid && setrgid(gid) < 0) rb_sys_fail(0);
	} else if (/* SAVED_GROUP_ID != gid && */ getegid() == gid) {
	    if (getgid() != gid) {
		if (setrgid(gid) < 0) rb_sys_fail(0);
		SAVED_GROUP_ID = gid;
	    } else {
		if (setrgid(SAVED_GROUP_ID) < 0) rb_sys_fail(0);
		SAVED_GROUP_ID = gid;
		if (setrgid(gid) < 0) rb_sys_fail(0);
	}
	} else if (/* getegid() != gid && */ getgid() == gid) {
	    if (setegid(gid) < 0) rb_sys_fail(0);
	    if (setrgid(SAVED_GROUP_ID) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	    if (setrgid(gid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_44BSD_SETGID
	if (getgid() == gid) {
	    /* (r,e,s)==(gid,?,?) ==> (gid,gid,gid) */
	    if (setgid(gid) < 0) rb_sys_fail(0);
	    SAVED_GROUP_ID = gid;
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_SETEGID
	if (getgid() == gid && SAVED_GROUP_ID == gid) {
	    if (setegid(gid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#elif defined HAVE_SETGID
	if (getgid() == gid && SAVED_GROUP_ID == gid) {
	    if (setgid(gid) < 0) rb_sys_fail(0);
	} else {
	    errno = EPERM;
	    rb_sys_fail(0);
	}
#else
	rb_notimplement();
#endif
    }
    return id;
}


/*
 *  call-seq:
 *     Process.euid           -> fixnum
 *     Process::UID.eid       -> fixnum
 *     Process::Sys.geteuid   -> fixnum
 *
 *  Returns the effective user ID for this process.
 *
 *     Process.euid   #=> 501
 */

static VALUE
proc_geteuid(VALUE obj)
{
    rb_uid_t euid = geteuid();
    return UIDT2NUM(euid);
}

#if defined(HAVE_SETRESUID) || defined(HAVE_SETREUID) || defined(HAVE_SETEUID) || defined(HAVE_SETUID) || defined(_POSIX_SAVED_IDS)
/*
 *  call-seq:
 *     Process.euid= integer
 *
 *  Sets the effective user ID for this process. Not available on all
 *  platforms.
 */

static VALUE
proc_seteuid(VALUE obj, VALUE euid)
{
    rb_uid_t uid;

    check_uid_switch();

    uid = NUM2UIDT(euid);
#if defined(HAVE_SETRESUID)
    if (setresuid(-1, uid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREUID
    if (setreuid(-1, uid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETEUID
    if (seteuid(uid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETUID
    if (uid == getuid()) {
	if (setuid(uid) < 0) rb_sys_fail(0);
    }
    else {
	rb_notimplement();
    }
#else
    rb_notimplement();
#endif
    return euid;
}
#endif

#if defined(HAVE_SETRESUID) || defined(HAVE_SETREUID) || defined(HAVE_SETEUID) || defined(HAVE_SETUID)
#define proc_seteuid_m proc_seteuid
#else
#define proc_seteuid_m rb_f_notimplement
#endif

static rb_uid_t
rb_seteuid_core(rb_uid_t euid)
{
    rb_uid_t uid;

    check_uid_switch();

    uid = getuid();

#if defined(HAVE_SETRESUID)
    if (uid != euid) {
	if (setresuid(-1,euid,euid) < 0) rb_sys_fail(0);
	SAVED_USER_ID = euid;
    } else {
	if (setresuid(-1,euid,-1) < 0) rb_sys_fail(0);
    }
#elif defined(HAVE_SETREUID) && !defined(OBSOLETE_SETREUID)
    if (setreuid(-1, euid) < 0) rb_sys_fail(0);
    if (uid != euid) {
	if (setreuid(euid,uid) < 0) rb_sys_fail(0);
	if (setreuid(uid,euid) < 0) rb_sys_fail(0);
	SAVED_USER_ID = euid;
    }
#elif defined HAVE_SETEUID
    if (seteuid(euid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETUID
    if (geteuid() == 0) rb_sys_fail(0);
    if (setuid(euid) < 0) rb_sys_fail(0);
#else
    rb_notimplement();
#endif
    return euid;
}


/*
 *  call-seq:
 *     Process::UID.grant_privilege(integer)   -> fixnum
 *     Process::UID.eid= integer               -> fixnum
 *
 *  Set the effective user ID, and if possible, the saved user ID of
 *  the process to the given _integer_. Returns the new
 *  effective user ID. Not available on all platforms.
 *
 *     [Process.uid, Process.euid]          #=> [0, 0]
 *     Process::UID.grant_privilege(31)     #=> 31
 *     [Process.uid, Process.euid]          #=> [0, 31]
 */

static VALUE
p_uid_grant_privilege(VALUE obj, VALUE id)
{
    rb_seteuid_core(NUM2UIDT(id));
    return id;
}


/*
 *  call-seq:
 *     Process.egid          -> fixnum
 *     Process::GID.eid      -> fixnum
 *     Process::Sys.geteid   -> fixnum
 *
 *  Returns the effective group ID for this process. Not available on
 *  all platforms.
 *
 *     Process.egid   #=> 500
 */

static VALUE
proc_getegid(VALUE obj)
{
    rb_gid_t egid = getegid();

    return GIDT2NUM(egid);
}

#if defined(HAVE_SETRESGID) || defined(HAVE_SETREGID) || defined(HAVE_SETEGID) || defined(HAVE_SETGID) || defined(_POSIX_SAVED_IDS)
/*
 *  call-seq:
 *     Process.egid = fixnum   -> fixnum
 *
 *  Sets the effective group ID for this process. Not available on all
 *  platforms.
 */

static VALUE
proc_setegid(VALUE obj, VALUE egid)
{
    rb_gid_t gid;

    check_gid_switch();

    gid = NUM2GIDT(egid);
#if defined(HAVE_SETRESGID)
    if (setresgid(-1, gid, -1) < 0) rb_sys_fail(0);
#elif defined HAVE_SETREGID
    if (setregid(-1, gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETEGID
    if (setegid(gid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETGID
    if (gid == getgid()) {
	if (setgid(gid) < 0) rb_sys_fail(0);
    }
    else {
	rb_notimplement();
    }
#else
    rb_notimplement();
#endif
    return egid;
}
#endif

#if defined(HAVE_SETRESGID) || defined(HAVE_SETREGID) || defined(HAVE_SETEGID) || defined(HAVE_SETGID)
#define proc_setegid_m proc_setegid
#else
#define proc_setegid_m rb_f_notimplement
#endif

static rb_gid_t
rb_setegid_core(rb_gid_t egid)
{
    rb_gid_t gid;

    check_gid_switch();

    gid = getgid();

#if defined(HAVE_SETRESGID)
    if (gid != egid) {
	if (setresgid(-1,egid,egid) < 0) rb_sys_fail(0);
	SAVED_GROUP_ID = egid;
    } else {
	if (setresgid(-1,egid,-1) < 0) rb_sys_fail(0);
    }
#elif defined(HAVE_SETREGID) && !defined(OBSOLETE_SETREGID)
    if (setregid(-1, egid) < 0) rb_sys_fail(0);
    if (gid != egid) {
	if (setregid(egid,gid) < 0) rb_sys_fail(0);
	if (setregid(gid,egid) < 0) rb_sys_fail(0);
	SAVED_GROUP_ID = egid;
    }
#elif defined HAVE_SETEGID
    if (setegid(egid) < 0) rb_sys_fail(0);
#elif defined HAVE_SETGID
    if (geteuid() == 0 /* root user */) rb_sys_fail(0);
    if (setgid(egid) < 0) rb_sys_fail(0);
#else
    rb_notimplement();
#endif
    return egid;
}


/*
 *  call-seq:
 *     Process::GID.grant_privilege(integer)    -> fixnum
 *     Process::GID.eid = integer               -> fixnum
 *
 *  Set the effective group ID, and if possible, the saved group ID of
 *  the process to the given _integer_. Returns the new
 *  effective group ID. Not available on all platforms.
 *
 *     [Process.gid, Process.egid]          #=> [0, 0]
 *     Process::GID.grant_privilege(31)     #=> 33
 *     [Process.gid, Process.egid]          #=> [0, 33]
 */

static VALUE
p_gid_grant_privilege(VALUE obj, VALUE id)
{
    rb_setegid_core(NUM2GIDT(id));
    return id;
}


/*
 *  call-seq:
 *     Process::UID.re_exchangeable?   -> true or false
 *
 *  Returns +true+ if the real and effective user IDs of a
 *  process may be exchanged on the current platform.
 *
 */

static VALUE
p_uid_exchangeable(void)
{
#if defined(HAVE_SETRESUID)
    return Qtrue;
#elif defined(HAVE_SETREUID) && !defined(OBSOLETE_SETREUID)
    return Qtrue;
#else
    return Qfalse;
#endif
}


/*
 *  call-seq:
 *     Process::UID.re_exchange   -> fixnum
 *
 *  Exchange real and effective user IDs and return the new effective
 *  user ID. Not available on all platforms.
 *
 *     [Process.uid, Process.euid]   #=> [0, 31]
 *     Process::UID.re_exchange      #=> 0
 *     [Process.uid, Process.euid]   #=> [31, 0]
 */

static VALUE
p_uid_exchange(VALUE obj)
{
    rb_uid_t uid, euid;

    check_uid_switch();

    uid = getuid();
    euid = geteuid();

#if defined(HAVE_SETRESUID)
    if (setresuid(euid, uid, uid) < 0) rb_sys_fail(0);
    SAVED_USER_ID = uid;
#elif defined(HAVE_SETREUID) && !defined(OBSOLETE_SETREUID)
    if (setreuid(euid,uid) < 0) rb_sys_fail(0);
    SAVED_USER_ID = uid;
#else
    rb_notimplement();
#endif
    return UIDT2NUM(uid);
}


/*
 *  call-seq:
 *     Process::GID.re_exchangeable?   -> true or false
 *
 *  Returns +true+ if the real and effective group IDs of a
 *  process may be exchanged on the current platform.
 *
 */

static VALUE
p_gid_exchangeable(void)
{
#if defined(HAVE_SETRESGID)
    return Qtrue;
#elif defined(HAVE_SETREGID) && !defined(OBSOLETE_SETREGID)
    return Qtrue;
#else
    return Qfalse;
#endif
}


/*
 *  call-seq:
 *     Process::GID.re_exchange   -> fixnum
 *
 *  Exchange real and effective group IDs and return the new effective
 *  group ID. Not available on all platforms.
 *
 *     [Process.gid, Process.egid]   #=> [0, 33]
 *     Process::GID.re_exchange      #=> 0
 *     [Process.gid, Process.egid]   #=> [33, 0]
 */

static VALUE
p_gid_exchange(VALUE obj)
{
    rb_gid_t gid, egid;

    check_gid_switch();

    gid = getgid();
    egid = getegid();

#if defined(HAVE_SETRESGID)
    if (setresgid(egid, gid, gid) < 0) rb_sys_fail(0);
    SAVED_GROUP_ID = gid;
#elif defined(HAVE_SETREGID) && !defined(OBSOLETE_SETREGID)
    if (setregid(egid,gid) < 0) rb_sys_fail(0);
    SAVED_GROUP_ID = gid;
#else
    rb_notimplement();
#endif
    return GIDT2NUM(gid);
}

/* [MG] :FIXME: Is this correct? I'm not sure how to phrase this. */

/*
 *  call-seq:
 *     Process::UID.sid_available?   -> true or false
 *
 *  Returns +true+ if the current platform has saved user
 *  ID functionality.
 *
 */

static VALUE
p_uid_have_saved_id(void)
{
#if defined(HAVE_SETRESUID) || defined(HAVE_SETEUID) || defined(_POSIX_SAVED_IDS)
    return Qtrue;
#else
    return Qfalse;
#endif
}


#if defined(HAVE_SETRESUID) || defined(HAVE_SETEUID) || defined(_POSIX_SAVED_IDS)
static VALUE
p_uid_sw_ensure(rb_uid_t id)
{
    under_uid_switch = 0;
    id = rb_seteuid_core(id);
    return UIDT2NUM(id);
}


/*
 *  call-seq:
 *     Process::UID.switch              -> fixnum
 *     Process::UID.switch {|| block}   -> object
 *
 *  Switch the effective and real user IDs of the current process. If
 *  a <em>block</em> is given, the user IDs will be switched back
 *  after the block is executed. Returns the new effective user ID if
 *  called without a block, and the return value of the block if one
 *  is given.
 *
 */

static VALUE
p_uid_switch(VALUE obj)
{
    rb_uid_t uid, euid;

    check_uid_switch();

    uid = getuid();
    euid = geteuid();

    if (uid != euid) {
	proc_seteuid(obj, UIDT2NUM(uid));
	if (rb_block_given_p()) {
	    under_uid_switch = 1;
	    return rb_ensure(rb_yield, Qnil, p_uid_sw_ensure, SAVED_USER_ID);
	} else {
	    return UIDT2NUM(euid);
	}
    } else if (euid != SAVED_USER_ID) {
	proc_seteuid(obj, UIDT2NUM(SAVED_USER_ID));
	if (rb_block_given_p()) {
	    under_uid_switch = 1;
	    return rb_ensure(rb_yield, Qnil, p_uid_sw_ensure, euid);
	} else {
	    return UIDT2NUM(uid);
	}
    } else {
	errno = EPERM;
	rb_sys_fail(0);
    }
}
#else
static VALUE
p_uid_sw_ensure(VALUE obj)
{
    under_uid_switch = 0;
    return p_uid_exchange(obj);
}

static VALUE
p_uid_switch(VALUE obj)
{
    rb_uid_t uid, euid;

    check_uid_switch();

    uid = getuid();
    euid = geteuid();

    if (uid == euid) {
	errno = EPERM;
	rb_sys_fail(0);
    }
    p_uid_exchange(obj);
    if (rb_block_given_p()) {
	under_uid_switch = 1;
	return rb_ensure(rb_yield, Qnil, p_uid_sw_ensure, obj);
    } else {
	return UIDT2NUM(euid);
    }
}
#endif


/* [MG] :FIXME: Is this correct? I'm not sure how to phrase this. */

/*
 *  call-seq:
 *     Process::GID.sid_available?   -> true or false
 *
 *  Returns +true+ if the current platform has saved group
 *  ID functionality.
 *
 */

static VALUE
p_gid_have_saved_id(void)
{
#if defined(HAVE_SETRESGID) || defined(HAVE_SETEGID) || defined(_POSIX_SAVED_IDS)
    return Qtrue;
#else
    return Qfalse;
#endif
}

#if defined(HAVE_SETRESGID) || defined(HAVE_SETEGID) || defined(_POSIX_SAVED_IDS)
static VALUE
p_gid_sw_ensure(rb_gid_t id)
{
    under_gid_switch = 0;
    id = rb_setegid_core(id);
    return GIDT2NUM(id);
}


/*
 *  call-seq:
 *     Process::GID.switch              -> fixnum
 *     Process::GID.switch {|| block}   -> object
 *
 *  Switch the effective and real group IDs of the current process. If
 *  a <em>block</em> is given, the group IDs will be switched back
 *  after the block is executed. Returns the new effective group ID if
 *  called without a block, and the return value of the block if one
 *  is given.
 *
 */

static VALUE
p_gid_switch(VALUE obj)
{
    rb_gid_t gid, egid;

    check_gid_switch();

    gid = getgid();
    egid = getegid();

    if (gid != egid) {
	proc_setegid(obj, GIDT2NUM(gid));
	if (rb_block_given_p()) {
	    under_gid_switch = 1;
	    return rb_ensure(rb_yield, Qnil, p_gid_sw_ensure, SAVED_GROUP_ID);
	} else {
	    return GIDT2NUM(egid);
	}
    }
    else if (egid != SAVED_GROUP_ID) {
	proc_setegid(obj, GIDT2NUM(SAVED_GROUP_ID));
	if (rb_block_given_p()) {
	    under_gid_switch = 1;
	    return rb_ensure(rb_yield, Qnil, p_gid_sw_ensure, egid);
	} else {
	    return GIDT2NUM(gid);
	}
    }
    else {
	errno = EPERM;
	rb_sys_fail(0);
    }
}
#else
static VALUE
p_gid_sw_ensure(VALUE obj)
{
    under_gid_switch = 0;
    return p_gid_exchange(obj);
}

static VALUE
p_gid_switch(VALUE obj)
{
    rb_gid_t gid, egid;

    check_gid_switch();

    gid = getgid();
    egid = getegid();

    if (gid == egid) {
	errno = EPERM;
	rb_sys_fail(0);
    }
    p_gid_exchange(obj);
    if (rb_block_given_p()) {
	under_gid_switch = 1;
	return rb_ensure(rb_yield, Qnil, p_gid_sw_ensure, obj);
    } else {
	return GIDT2NUM(egid);
    }
}
#endif


#if defined(HAVE_TIMES)
/*
 *  call-seq:
 *     Process.times   -> aStructTms
 *
 *  Returns a <code>Tms</code> structure (see <code>Struct::Tms</code>)
 *  that contains user and system CPU times for this process,
 *  and also for children processes.
 *
 *     t = Process.times
 *     [ t.utime, t.stime, t.cutime, t.cstime ]   #=> [0.0, 0.02, 0.00, 0.00]
 */

VALUE
rb_proc_times(VALUE obj)
{
    const double hertz =
#ifdef HAVE__SC_CLK_TCK
	(double)sysconf(_SC_CLK_TCK);
#else
#ifndef HZ
# ifdef CLK_TCK
#   define HZ CLK_TCK
# else
#   define HZ 60
# endif
#endif /* HZ */
	HZ;
#endif
    struct tms buf;
    volatile VALUE utime, stime, cutime, sctime;

    times(&buf);
    return rb_struct_new(rb_cProcessTms,
			 utime = DBL2NUM(buf.tms_utime / hertz),
			 stime = DBL2NUM(buf.tms_stime / hertz),
			 cutime = DBL2NUM(buf.tms_cutime / hertz),
			 sctime = DBL2NUM(buf.tms_cstime / hertz));
}
#else
#define rb_proc_times rb_f_notimplement
#endif

VALUE rb_mProcess;
VALUE rb_mProcUID;
VALUE rb_mProcGID;
VALUE rb_mProcID_Syscall;


/*
 *  The <code>Process</code> module is a collection of methods used to
 *  manipulate processes.
 */

void
Init_process(void)
{
    rb_define_virtual_variable("$?", rb_last_status_get, 0);
    rb_define_virtual_variable("$$", get_pid, 0);
    rb_define_global_function("exec", rb_f_exec, -1);
    rb_define_global_function("fork", rb_f_fork, 0);
    rb_define_global_function("exit!", rb_f_exit_bang, -1);
    rb_define_global_function("system", rb_f_system, -1);
    rb_define_global_function("spawn", rb_f_spawn, -1);
    rb_define_global_function("sleep", rb_f_sleep, -1);
    rb_define_global_function("exit", rb_f_exit, -1);
    rb_define_global_function("abort", rb_f_abort, -1);

    rb_mProcess = rb_define_module("Process");

#ifdef WNOHANG
    /* see Process.wait */
    rb_define_const(rb_mProcess, "WNOHANG", INT2FIX(WNOHANG));
#else
    /* see Process.wait */
    rb_define_const(rb_mProcess, "WNOHANG", INT2FIX(0));
#endif
#ifdef WUNTRACED
    /* see Process.wait */
    rb_define_const(rb_mProcess, "WUNTRACED", INT2FIX(WUNTRACED));
#else
    /* see Process.wait */
    rb_define_const(rb_mProcess, "WUNTRACED", INT2FIX(0));
#endif

    rb_define_singleton_method(rb_mProcess, "exec", rb_f_exec, -1);
    rb_define_singleton_method(rb_mProcess, "fork", rb_f_fork, 0);
    rb_define_singleton_method(rb_mProcess, "spawn", rb_f_spawn, -1);
    rb_define_singleton_method(rb_mProcess, "exit!", rb_f_exit_bang, -1);
    rb_define_singleton_method(rb_mProcess, "exit", rb_f_exit, -1);
    rb_define_singleton_method(rb_mProcess, "abort", rb_f_abort, -1);

    rb_define_module_function(rb_mProcess, "kill", rb_f_kill, -1); /* in signal.c */
    rb_define_module_function(rb_mProcess, "wait", proc_wait, -1);
    rb_define_module_function(rb_mProcess, "wait2", proc_wait2, -1);
    rb_define_module_function(rb_mProcess, "waitpid", proc_wait, -1);
    rb_define_module_function(rb_mProcess, "waitpid2", proc_wait2, -1);
    rb_define_module_function(rb_mProcess, "waitall", proc_waitall, 0);
    rb_define_module_function(rb_mProcess, "detach", proc_detach, 1);

    rb_cProcessStatus = rb_define_class_under(rb_mProcess, "Status", rb_cObject);
    rb_undef_method(CLASS_OF(rb_cProcessStatus), "new");

    rb_define_method(rb_cProcessStatus, "==", pst_equal, 1);
    rb_define_method(rb_cProcessStatus, "&", pst_bitand, 1);
    rb_define_method(rb_cProcessStatus, ">>", pst_rshift, 1);
    rb_define_method(rb_cProcessStatus, "to_i", pst_to_i, 0);
    rb_define_method(rb_cProcessStatus, "to_s", pst_to_s, 0);
    rb_define_method(rb_cProcessStatus, "inspect", pst_inspect, 0);

    rb_define_method(rb_cProcessStatus, "pid", pst_pid, 0);

    rb_define_method(rb_cProcessStatus, "stopped?", pst_wifstopped, 0);
    rb_define_method(rb_cProcessStatus, "stopsig", pst_wstopsig, 0);
    rb_define_method(rb_cProcessStatus, "signaled?", pst_wifsignaled, 0);
    rb_define_method(rb_cProcessStatus, "termsig", pst_wtermsig, 0);
    rb_define_method(rb_cProcessStatus, "exited?", pst_wifexited, 0);
    rb_define_method(rb_cProcessStatus, "exitstatus", pst_wexitstatus, 0);
    rb_define_method(rb_cProcessStatus, "success?", pst_success_p, 0);
    rb_define_method(rb_cProcessStatus, "coredump?", pst_wcoredump, 0);

    rb_define_module_function(rb_mProcess, "pid", get_pid, 0);
    rb_define_module_function(rb_mProcess, "ppid", get_ppid, 0);

    rb_define_module_function(rb_mProcess, "getpgrp", proc_getpgrp, 0);
    rb_define_module_function(rb_mProcess, "setpgrp", proc_setpgrp, 0);
    rb_define_module_function(rb_mProcess, "getpgid", proc_getpgid, 1);
    rb_define_module_function(rb_mProcess, "setpgid", proc_setpgid, 2);

    rb_define_module_function(rb_mProcess, "setsid", proc_setsid, 0);

    rb_define_module_function(rb_mProcess, "getpriority", proc_getpriority, 2);
    rb_define_module_function(rb_mProcess, "setpriority", proc_setpriority, 3);

#ifdef HAVE_GETPRIORITY
    /* see Process.setpriority */
    rb_define_const(rb_mProcess, "PRIO_PROCESS", INT2FIX(PRIO_PROCESS));
    /* see Process.setpriority */
    rb_define_const(rb_mProcess, "PRIO_PGRP", INT2FIX(PRIO_PGRP));
    /* see Process.setpriority */
    rb_define_const(rb_mProcess, "PRIO_USER", INT2FIX(PRIO_USER));
#endif

    rb_define_module_function(rb_mProcess, "getrlimit", proc_getrlimit, 1);
    rb_define_module_function(rb_mProcess, "setrlimit", proc_setrlimit, -1);
#if defined(RLIM2NUM) && defined(RLIM_INFINITY)
    {
        VALUE inf = RLIM2NUM(RLIM_INFINITY);
#ifdef RLIM_SAVED_MAX
	{
	    VALUE v = RLIM_INFINITY == RLIM_SAVED_MAX ? inf : RLIM2NUM(RLIM_SAVED_MAX);
	    /* see Process.setrlimit */
	    rb_define_const(rb_mProcess, "RLIM_SAVED_MAX", v);
	}
#endif
	/* see Process.setrlimit */
        rb_define_const(rb_mProcess, "RLIM_INFINITY", inf);
#ifdef RLIM_SAVED_CUR
	{
	    VALUE v = RLIM_INFINITY == RLIM_SAVED_CUR ? inf : RLIM2NUM(RLIM_SAVED_CUR);
	    /* see Process.setrlimit */
	    rb_define_const(rb_mProcess, "RLIM_SAVED_CUR", v);
	}
#endif
    }
#ifdef RLIMIT_AS
    /* Maximum size of the process's virtual memory (address space) in bytes.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_AS", INT2FIX(RLIMIT_AS));
#endif
#ifdef RLIMIT_CORE
    /* Maximum size of the core file.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_CORE", INT2FIX(RLIMIT_CORE));
#endif
#ifdef RLIMIT_CPU
    /* CPU time limit in seconds.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_CPU", INT2FIX(RLIMIT_CPU));
#endif
#ifdef RLIMIT_DATA
    /* Maximum size of the process's data segment.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_DATA", INT2FIX(RLIMIT_DATA));
#endif
#ifdef RLIMIT_FSIZE
    /* Maximum size of files that the process may create.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_FSIZE", INT2FIX(RLIMIT_FSIZE));
#endif
#ifdef RLIMIT_MEMLOCK
    /* Maximum number of bytes of memory that may be locked into RAM.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_MEMLOCK", INT2FIX(RLIMIT_MEMLOCK));
#endif
#ifdef RLIMIT_MSGQUEUE
    /* Specifies the limit on the number of bytes that can be allocated
     * for POSIX message queues for the real user ID of the calling process.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_MSGQUEUE", INT2FIX(RLIMIT_MSGQUEUE));
#endif
#ifdef RLIMIT_NICE
    /* Specifies a ceiling to which the process's nice value can be raised.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_NICE", INT2FIX(RLIMIT_NICE));
#endif
#ifdef RLIMIT_NOFILE
    /* Specifies a value one greater than the maximum file descriptor
     * number that can be opened by this process.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_NOFILE", INT2FIX(RLIMIT_NOFILE));
#endif
#ifdef RLIMIT_NPROC
    /* The maximum number of processes that can be created for the
     * real user ID of the calling process.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_NPROC", INT2FIX(RLIMIT_NPROC));
#endif
#ifdef RLIMIT_RSS
    /* Specifies the limit (in pages) of the process's resident set.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_RSS", INT2FIX(RLIMIT_RSS));
#endif
#ifdef RLIMIT_RTPRIO
    /* Specifies a ceiling on the real-time priority that may be set for this process.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_RTPRIO", INT2FIX(RLIMIT_RTPRIO));
#endif
#ifdef RLIMIT_RTTIME
    /* Specifies limit on CPU time this process scheduled under a real-time
     * scheduling policy can consume.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_RTTIME", INT2FIX(RLIMIT_RTTIME));
#endif
#ifdef RLIMIT_SBSIZE
    /* Maximum size of the socket buffer.
     */
    rb_define_const(rb_mProcess, "RLIMIT_SBSIZE", INT2FIX(RLIMIT_SBSIZE));
#endif
#ifdef RLIMIT_SIGPENDING
    /* Specifies a limit on the number of signals that may be queued for
     * the real user ID of the calling process.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_SIGPENDING", INT2FIX(RLIMIT_SIGPENDING));
#endif
#ifdef RLIMIT_STACK
    /* Maximum size of the stack, in bytes.
     *
     * see the system getrlimit(2) manual for details.
     */
    rb_define_const(rb_mProcess, "RLIMIT_STACK", INT2FIX(RLIMIT_STACK));
#endif
#endif

    rb_define_module_function(rb_mProcess, "uid", proc_getuid, 0);
    rb_define_module_function(rb_mProcess, "uid=", proc_setuid, 1);
    rb_define_module_function(rb_mProcess, "gid", proc_getgid, 0);
    rb_define_module_function(rb_mProcess, "gid=", proc_setgid, 1);
    rb_define_module_function(rb_mProcess, "euid", proc_geteuid, 0);
    rb_define_module_function(rb_mProcess, "euid=", proc_seteuid_m, 1);
    rb_define_module_function(rb_mProcess, "egid", proc_getegid, 0);
    rb_define_module_function(rb_mProcess, "egid=", proc_setegid_m, 1);
    rb_define_module_function(rb_mProcess, "initgroups", proc_initgroups, 2);
    rb_define_module_function(rb_mProcess, "groups", proc_getgroups, 0);
    rb_define_module_function(rb_mProcess, "groups=", proc_setgroups, 1);
    rb_define_module_function(rb_mProcess, "maxgroups", proc_getmaxgroups, 0);
    rb_define_module_function(rb_mProcess, "maxgroups=", proc_setmaxgroups, 1);

    rb_define_module_function(rb_mProcess, "daemon", proc_daemon, -1);

    rb_define_module_function(rb_mProcess, "times", rb_proc_times, 0);

#if defined(HAVE_TIMES) || defined(_WIN32)
    rb_cProcessTms = rb_struct_define("Tms", "utime", "stime", "cutime", "cstime", NULL);
#endif

    SAVED_USER_ID = geteuid();
    SAVED_GROUP_ID = getegid();

    rb_mProcUID = rb_define_module_under(rb_mProcess, "UID");
    rb_mProcGID = rb_define_module_under(rb_mProcess, "GID");

    rb_define_module_function(rb_mProcUID, "rid", proc_getuid, 0);
    rb_define_module_function(rb_mProcGID, "rid", proc_getgid, 0);
    rb_define_module_function(rb_mProcUID, "eid", proc_geteuid, 0);
    rb_define_module_function(rb_mProcGID, "eid", proc_getegid, 0);
    rb_define_module_function(rb_mProcUID, "change_privilege", p_uid_change_privilege, 1);
    rb_define_module_function(rb_mProcGID, "change_privilege", p_gid_change_privilege, 1);
    rb_define_module_function(rb_mProcUID, "grant_privilege", p_uid_grant_privilege, 1);
    rb_define_module_function(rb_mProcGID, "grant_privilege", p_gid_grant_privilege, 1);
    rb_define_alias(rb_singleton_class(rb_mProcUID), "eid=", "grant_privilege");
    rb_define_alias(rb_singleton_class(rb_mProcGID), "eid=", "grant_privilege");
    rb_define_module_function(rb_mProcUID, "re_exchange", p_uid_exchange, 0);
    rb_define_module_function(rb_mProcGID, "re_exchange", p_gid_exchange, 0);
    rb_define_module_function(rb_mProcUID, "re_exchangeable?", p_uid_exchangeable, 0);
    rb_define_module_function(rb_mProcGID, "re_exchangeable?", p_gid_exchangeable, 0);
    rb_define_module_function(rb_mProcUID, "sid_available?", p_uid_have_saved_id, 0);
    rb_define_module_function(rb_mProcGID, "sid_available?", p_gid_have_saved_id, 0);
    rb_define_module_function(rb_mProcUID, "switch", p_uid_switch, 0);
    rb_define_module_function(rb_mProcGID, "switch", p_gid_switch, 0);

    rb_mProcID_Syscall = rb_define_module_under(rb_mProcess, "Sys");

    rb_define_module_function(rb_mProcID_Syscall, "getuid", proc_getuid, 0);
    rb_define_module_function(rb_mProcID_Syscall, "geteuid", proc_geteuid, 0);
    rb_define_module_function(rb_mProcID_Syscall, "getgid", proc_getgid, 0);
    rb_define_module_function(rb_mProcID_Syscall, "getegid", proc_getegid, 0);

    rb_define_module_function(rb_mProcID_Syscall, "setuid", p_sys_setuid, 1);
    rb_define_module_function(rb_mProcID_Syscall, "setgid", p_sys_setgid, 1);

    rb_define_module_function(rb_mProcID_Syscall, "setruid", p_sys_setruid, 1);
    rb_define_module_function(rb_mProcID_Syscall, "setrgid", p_sys_setrgid, 1);

    rb_define_module_function(rb_mProcID_Syscall, "seteuid", p_sys_seteuid, 1);
    rb_define_module_function(rb_mProcID_Syscall, "setegid", p_sys_setegid, 1);

    rb_define_module_function(rb_mProcID_Syscall, "setreuid", p_sys_setreuid, 2);
    rb_define_module_function(rb_mProcID_Syscall, "setregid", p_sys_setregid, 2);

    rb_define_module_function(rb_mProcID_Syscall, "setresuid", p_sys_setresuid, 3);
    rb_define_module_function(rb_mProcID_Syscall, "setresgid", p_sys_setresgid, 3);
    rb_define_module_function(rb_mProcID_Syscall, "issetugid", p_sys_issetugid, 0);
}
