##### http://autoconf-archive.cryp.to/acx_func_fork.html
#
# SYNOPSIS
#
#   ACX_FUNC_FORK
#
# DESCRIPTION
#
#   Check to for a working fork. Use to provide a workaround for
#   systems that don't have a working fork. For example, the workaround
#   for the fork()/exec() sequence for DOS is to use spawn.
#
#   Defines HAVE_NO_FORK is fork() doesn't work or isn't implemented.
#
# LAST MODIFICATION
#
#   2000-07-19
#
# COPYLEFT
#
#   Copyright (c) 2000 Mark Elbrecht <snowball3@bigfoot.com>
#
#   This program is free software; you can redistribute it and/or
#   modify it under the terms of the GNU General Public License as
#   published by the Free Software Foundation; either version 2 of the
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#
#   This program is distributed in the hope that it will be useful, but
#   WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
#   General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program; if not, write to the Free Software
#   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
#   02111-1307, USA.
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AC_DEFUN([ACX_FUNC_FORK],
[AC_MSG_CHECKING(for a working fork)
AC_CACHE_VAL(acx_cv_func_fork_works,
[AC_REQUIRE([AC_TYPE_PID_T])
AC_REQUIRE([AC_HEADER_SYS_WAIT])
AC_TRY_RUN([#include <sys/types.h>
#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

int main()
{
  int status;
  pid_t child = fork();

  if (child < 0) /* Error */
    return (1);
  else if (child == 0) /* Child */
    return (0);

  /* Parent */
  status = (wait(&status) != child);
  return  (status >= 0) ? 0 : 1;
}
], acx_cv_func_fork_works=yes, acx_cv_func_fork_works=no, acx_cv_func_fork_works=no)
])
AC_MSG_RESULT($acx_cv_func_fork_works)
if test $acx_cv_func_fork_works = no; then
  AC_DEFINE(HAVE_NO_FORK)
fi
])