source: kBuild/vendor/gnumake/2005-05-16/job.c

/* Job execution and handling for GNU Make.
Copyright (C) 1988,1989,1990,1991,1992,1993,1994,1995,1996,1997,1999,
2000,2001,2002,2003,2004,2005 Free Software Foundation, Inc.
This file is part of GNU Make.

GNU Make 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, or (at your option)
any later version.

GNU Make 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 GNU Make; see the file COPYING.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#include "make.h"

#include <assert.h>

#include "job.h"
#include "debug.h"
#include "filedef.h"
#include "commands.h"
#include "variable.h"
#include "debug.h"

#include <string.h>

/* Default shell to use.  */
#ifdef WINDOWS32

char *default_shell = "sh.exe";
int no_default_sh_exe = 1;
int batch_mode_shell = 1;

#elif defined (_AMIGA)

char default_shell[] = "";
extern int MyExecute (char **);
int batch_mode_shell = 0;

#elif defined (__MSDOS__)

/* The default shell is a pointer so we can change it if Makefile
   says so.  It is without an explicit path so we get a chance
   to search the $PATH for it (since MSDOS doesn't have standard
   directories we could trust).  */
char *default_shell = "command.com";
int batch_mode_shell = 0;

#elif defined (__EMX__)

char *default_shell = "/bin/sh";
int batch_mode_shell = 0;

#elif defined (VMS)

# include <descrip.h>
char default_shell[] = "";
int batch_mode_shell = 0;

#elif defined (__riscos__)

char default_shell[] = "";
int batch_mode_shell = 0;

#else

char default_shell[] = "/bin/sh";
int batch_mode_shell = 0;

#endif

#ifdef __MSDOS__
# include <process.h>
static int execute_by_shell;
static int dos_pid = 123;
int dos_status;
int dos_command_running;
#endif /* __MSDOS__ */

#ifdef _AMIGA
# include <proto/dos.h>
static int amiga_pid = 123;
static int amiga_status;
static char amiga_bname[32];
static int amiga_batch_file;
#endif /* Amiga.  */

#ifdef VMS
# ifndef __GNUC__
#   include <processes.h>
# endif
# include <starlet.h>
# include <lib$routines.h>
#endif

#ifdef WINDOWS32
# include <windows.h>
# include <io.h>
# include <process.h>
# include "sub_proc.h"
# include "w32err.h"
# include "pathstuff.h"
#endif /* WINDOWS32 */

#ifdef __EMX__
# include <process.h>
#endif

#if defined (HAVE_SYS_WAIT_H) || defined (HAVE_UNION_WAIT)
# include <sys/wait.h>
#endif

#ifdef HAVE_WAITPID
# define WAIT_NOHANG(status)    waitpid (-1, (status), WNOHANG)
#else   /* Don't have waitpid.  */
# ifdef HAVE_WAIT3
#  ifndef wait3
extern int wait3 ();
#  endif
#  define WAIT_NOHANG(status)   wait3 ((status), WNOHANG, (struct rusage *) 0)
# endif /* Have wait3.  */
#endif /* Have waitpid.  */

#if !defined (wait) && !defined (POSIX)
extern int wait ();
#endif

#ifndef HAVE_UNION_WAIT

# define WAIT_T int

# ifndef WTERMSIG
#  define WTERMSIG(x) ((x) & 0x7f)
# endif
# ifndef WCOREDUMP
#  define WCOREDUMP(x) ((x) & 0x80)
# endif
# ifndef WEXITSTATUS
#  define WEXITSTATUS(x) (((x) >> 8) & 0xff)
# endif
# ifndef WIFSIGNALED
#  define WIFSIGNALED(x) (WTERMSIG (x) != 0)
# endif
# ifndef WIFEXITED
#  define WIFEXITED(x) (WTERMSIG (x) == 0)
# endif

#else   /* Have `union wait'.  */

# define WAIT_T union wait
# ifndef WTERMSIG
#  define WTERMSIG(x) ((x).w_termsig)
# endif
# ifndef WCOREDUMP
#  define WCOREDUMP(x) ((x).w_coredump)
# endif
# ifndef WEXITSTATUS
#  define WEXITSTATUS(x) ((x).w_retcode)
# endif
# ifndef WIFSIGNALED
#  define WIFSIGNALED(x) (WTERMSIG(x) != 0)
# endif
# ifndef WIFEXITED
#  define WIFEXITED(x) (WTERMSIG(x) == 0)
# endif

#endif  /* Don't have `union wait'.  */

#ifndef HAVE_UNISTD_H
extern int dup2 ();
extern int execve ();
extern void _exit ();
# ifndef VMS
extern int geteuid ();
extern int getegid ();
extern int setgid ();
extern int getgid ();
# endif
#endif

extern char *allocated_variable_expand_for_file PARAMS ((char *line, struct file *file));

extern int getloadavg PARAMS ((double loadavg[], int nelem));
extern int start_remote_job PARAMS ((char **argv, char **envp, int stdin_fd,
                int *is_remote, int *id_ptr, int *used_stdin));
extern int start_remote_job_p PARAMS ((int));
extern int remote_status PARAMS ((int *exit_code_ptr, int *signal_ptr,
                int *coredump_ptr, int block));

RETSIGTYPE child_handler PARAMS ((int));
static void free_child PARAMS ((struct child *));
static void start_job_command PARAMS ((struct child *child));
static int load_too_high PARAMS ((void));
static int job_next_command PARAMS ((struct child *));
static int start_waiting_job PARAMS ((struct child *));


/* Chain of all live (or recently deceased) children.  */

struct child *children = 0;

/* Number of children currently running.  */

unsigned int job_slots_used = 0;

/* Nonzero if the `good' standard input is in use.  */

static int good_stdin_used = 0;

/* Chain of children waiting to run until the load average goes down.  */

static struct child *waiting_jobs = 0;

/* Non-zero if we use a *real* shell (always so on Unix).  */

int unixy_shell = 1;

/* Number of jobs started in the current second.  */

unsigned long job_counter = 0;

/* Number of jobserver tokens this instance is currently using.  */

unsigned int jobserver_tokens = 0;


#ifdef WINDOWS32
/*
 * The macro which references this function is defined in make.h.
 */
int
w32_kill(int pid, int sig)
{
  return ((process_kill((HANDLE)pid, sig) == TRUE) ? 0 : -1);
}

/* This function creates a temporary file name with the given extension
 * the unixy param controls both the extension and the path separator
 * return an xmalloc'ed string of a newly created temp file or die.  */
static char *
create_batch_filename(char const *base, int unixy)
{
  const char *const ext = unixy ? "sh" : "bat";
  const char *error = NULL;
  char temp_path[MAXPATHLEN]; /* need to know its length */
  unsigned path_size = GetTempPath(sizeof temp_path, temp_path);
  int path_is_dot = 0;
  unsigned uniq = 1;
  const unsigned sizemax = strlen (base) + strlen (ext) + 10;

  if (path_size == 0)
    {
      path_size = GetCurrentDirectory (sizeof temp_path, temp_path);
      path_is_dot = 1;
    }

  while (path_size > 0 &&
         path_size + sizemax < sizeof temp_path &&
         uniq < 0x10000)
    {
      unsigned size = sprintf (temp_path + path_size,
                               "%s%s-%x.%s",
                               temp_path[path_size - 1] == '\\' ? "" : "\\",
                               base, uniq, ext);
      HANDLE h = CreateFile (temp_path,  /* file name */
                             GENERIC_READ | GENERIC_WRITE, /* desired access */
                             0,                            /* no share mode */
                             NULL,                         /* default security attributes */
                             CREATE_NEW,                   /* creation disposition */
                             FILE_ATTRIBUTE_NORMAL |       /* flags and attributes */
                             FILE_ATTRIBUTE_TEMPORARY,     /* we'll delete it */
                             NULL);                        /* no template file */

      if (h == INVALID_HANDLE_VALUE)
        {
          const DWORD er = GetLastError();

          if (er == ERROR_FILE_EXISTS || er == ERROR_ALREADY_EXISTS)
            ++uniq;

          /* the temporary path is not guaranteed to exist */
          else if (path_is_dot == 0)
            {
              path_size = GetCurrentDirectory (sizeof temp_path, temp_path);
              path_is_dot = 1;
            }

          else
            {
              error = map_windows32_error_to_string (er);
              break;
            }
        }
      else
        {
          const unsigned final_size = path_size + size + 1;
          char *const path = (char *) xmalloc (final_size);
          memcpy (path, temp_path, final_size);
          CloseHandle (h);
          if (unixy)
            {
              char *p;
              int ch;
              for (p = path; (ch = *p) != 0; ++p)
                if (ch == '\\')
                  *p = '/';
            }
          return path; /* good return */
        }
    }

  if (error == NULL)
    error = _("Cannot create a temporary file\n");
  fatal (NILF, error);

  /* not reached */
  return NULL;
}
#endif /* WINDOWS32 */

#ifdef __EMX__
/* returns whether path is assumed to be a unix like shell. */
int
_is_unixy_shell (const char *path)
{
  /* list of non unix shells */
  const char *known_os2shells[] = {
    "cmd.exe",
    "cmd",
    "4os2.exe",
    "4os2",
    "4dos.exe",
    "4dos",
    "command.com",
    "command",
    NULL
  };

  /* find the rightmost '/' or '\\' */
  const char *name = strrchr (path, '/');
  const char *p = strrchr (path, '\\');
  unsigned i;

  if (name && p)    /* take the max */
    name = (name > p) ? name : p;
  else if (p)       /* name must be 0 */
    name = p;
  else if (!name)   /* name and p must be 0 */
    name = path;

  if (*name == '/' || *name == '\\') name++;

  i = 0;
  while (known_os2shells[i] != NULL) {
    if (stricmp (name, known_os2shells[i]) == 0) /* strcasecmp() */
      return 0; /* not a unix shell */
    i++;
  }

  /* in doubt assume a unix like shell */
  return 1;
}
#endif /* __EMX__ */



/* Write an error message describing the exit status given in
   EXIT_CODE, EXIT_SIG, and COREDUMP, for the target TARGET_NAME.
   Append "(ignored)" if IGNORED is nonzero.  */

static void
child_error (char *target_name, int exit_code, int exit_sig, int coredump,
             int ignored)
{
  if (ignored && silent_flag)
    return;

#ifdef VMS
  if (!(exit_code & 1))
      error (NILF,
             (ignored ? _("*** [%s] Error 0x%x (ignored)")
              : _("*** [%s] Error 0x%x")),
             target_name, exit_code);
#else
  if (exit_sig == 0)
    error (NILF, ignored ? _("[%s] Error %d (ignored)") :
           _("*** [%s] Error %d"),
           target_name, exit_code);
  else
    error (NILF, "*** [%s] %s%s",
           target_name, strsignal (exit_sig),
           coredump ? _(" (core dumped)") : "");
#endif /* VMS */
}



/* Handle a dead child.  This handler may or may not ever be installed.

   If we're using the jobserver feature, we need it.  First, installing it
   ensures the read will interrupt on SIGCHLD.  Second, we close the dup'd
   read FD to ensure we don't enter another blocking read without reaping all
   the dead children.  In this case we don't need the dead_children count.

   If we don't have either waitpid or wait3, then make is unreliable, but we
   use the dead_children count to reap children as best we can.  */

static unsigned int dead_children = 0;

RETSIGTYPE
child_handler (int sig UNUSED)
{
  ++dead_children;

  if (job_rfd >= 0)
    {
      close (job_rfd);
      job_rfd = -1;
    }

#ifdef __EMX__
  /* The signal handler must called only once! */
  signal (SIGCHLD, SIG_DFL);
#endif

  /* This causes problems if the SIGCHLD interrupts a printf().
  DB (DB_JOBS, (_("Got a SIGCHLD; %u unreaped children.\n"), dead_children));
  */
}

extern int shell_function_pid, shell_function_completed;

/* Reap all dead children, storing the returned status and the new command
   state (`cs_finished') in the `file' member of the `struct child' for the
   dead child, and removing the child from the chain.  In addition, if BLOCK
   nonzero, we block in this function until we've reaped at least one
   complete child, waiting for it to die if necessary.  If ERR is nonzero,
   print an error message first.  */

void
reap_children (int block, int err)
{
  WAIT_T status;
  /* Initially, assume we have some.  */
  int reap_more = 1;

#ifdef WAIT_NOHANG
# define REAP_MORE reap_more
#else
# define REAP_MORE dead_children
#endif

  /* As long as:

       We have at least one child outstanding OR a shell function in progress,
         AND
       We're blocking for a complete child OR there are more children to reap

     we'll keep reaping children.  */

  while ((children != 0 || shell_function_pid != 0)
         && (block || REAP_MORE))
    {
      int remote = 0;
      pid_t pid;
      int exit_code, exit_sig, coredump;
      register struct child *lastc, *c;
      int child_failed;
      int any_remote, any_local;

      if (err && block)
        {
          /* We might block for a while, so let the user know why.  */
          fflush (stdout);
          error (NILF, _("*** Waiting for unfinished jobs...."));
        }

      /* We have one less dead child to reap.  As noted in
         child_handler() above, this count is completely unimportant for
         all modern, POSIX-y systems that support wait3() or waitpid().
         The rest of this comment below applies only to early, broken
         pre-POSIX systems.  We keep the count only because... it's there...

         The test and decrement are not atomic; if it is compiled into:
                register = dead_children - 1;
                dead_children = register;
         a SIGCHLD could come between the two instructions.
         child_handler increments dead_children.
         The second instruction here would lose that increment.  But the
         only effect of dead_children being wrong is that we might wait
         longer than necessary to reap a child, and lose some parallelism;
         and we might print the "Waiting for unfinished jobs" message above
         when not necessary.  */

      if (dead_children > 0)
        --dead_children;

      any_remote = 0;
      any_local = shell_function_pid != 0;
      for (c = children; c != 0; c = c->next)
        {
          any_remote |= c->remote;
          any_local |= ! c->remote;
          DB (DB_JOBS, (_("Live child 0x%08lx (%s) PID %ld %s\n"),
                        (unsigned long int) c, c->file->name,
                        (long) c->pid, c->remote ? _(" (remote)") : ""));
#ifdef VMS
          break;
#endif
        }

      /* First, check for remote children.  */
      if (any_remote)
        pid = remote_status (&exit_code, &exit_sig, &coredump, 0);
      else
        pid = 0;

      if (pid > 0)
        /* We got a remote child.  */
        remote = 1;
      else if (pid < 0)
        {
          /* A remote status command failed miserably.  Punt.  */
        remote_status_lose:
          pfatal_with_name ("remote_status");
        }
      else
        {
          /* No remote children.  Check for local children.  */
#if !defined(__MSDOS__) && !defined(_AMIGA) && !defined(WINDOWS32)
          if (any_local)
            {
#ifdef VMS
              static void vmsWaitForChildren PARAMS ((int *));
              vmsWaitForChildren (&status);
              pid = c->pid;
#else
#ifdef WAIT_NOHANG
              if (!block)
                pid = WAIT_NOHANG (&status);
              else
#endif
                pid = wait (&status);
#endif /* !VMS */
            }
          else
            pid = 0;

          if (pid < 0)
            {
              /* The wait*() failed miserably.  Punt.  */
              pfatal_with_name ("wait");
            }
          else if (pid > 0)
            {
              /* We got a child exit; chop the status word up.  */
              exit_code = WEXITSTATUS (status);
              exit_sig = WIFSIGNALED (status) ? WTERMSIG (status) : 0;
              coredump = WCOREDUMP (status);

              /* If we have started jobs in this second, remove one.  */
              if (job_counter)
                --job_counter;
            }
          else
            {
              /* No local children are dead.  */
              reap_more = 0;

              if (!block || !any_remote)
                break;

              /* Now try a blocking wait for a remote child.  */
              pid = remote_status (&exit_code, &exit_sig, &coredump, 1);
              if (pid < 0)
                goto remote_status_lose;
              else if (pid == 0)
                /* No remote children either.  Finally give up.  */
                break;

              /* We got a remote child.  */
              remote = 1;
            }
#endif /* !__MSDOS__, !Amiga, !WINDOWS32.  */

#ifdef __MSDOS__
          /* Life is very different on MSDOS.  */
          pid = dos_pid - 1;
          status = dos_status;
          exit_code = WEXITSTATUS (status);
          if (exit_code == 0xff)
            exit_code = -1;
          exit_sig = WIFSIGNALED (status) ? WTERMSIG (status) : 0;
          coredump = 0;
#endif /* __MSDOS__ */
#ifdef _AMIGA
          /* Same on Amiga */
          pid = amiga_pid - 1;
          status = amiga_status;
          exit_code = amiga_status;
          exit_sig = 0;
          coredump = 0;
#endif /* _AMIGA */
#ifdef WINDOWS32
          {
            HANDLE hPID;
            int err;
            exit_code = 0;
            exit_sig = 0;
            coredump = 0;

            /* wait for anything to finish */
            hPID = process_wait_for_any();
            if (hPID)
              {

                /* was an error found on this process? */
                err = process_last_err(hPID);

                /* get exit data */
                exit_code = process_exit_code(hPID);

                if (err)
                  fprintf(stderr, "make (e=%d): %s",
                          exit_code, map_windows32_error_to_string(exit_code));

                /* signal */
                exit_sig = process_signal(hPID);

                /* cleanup process */
                process_cleanup(hPID);

                coredump = 0;
              }
            pid = (pid_t) hPID;
          }
#endif /* WINDOWS32 */
        }

      /* Check if this is the child of the `shell' function.  */
      if (!remote && pid == shell_function_pid)
        {
          /* It is.  Leave an indicator for the `shell' function.  */
          if (exit_sig == 0 && exit_code == 127)
            shell_function_completed = -1;
          else
            shell_function_completed = 1;
          break;
        }

      child_failed = exit_sig != 0 || exit_code != 0;

      /* Search for a child matching the deceased one.  */
      lastc = 0;
      for (c = children; c != 0; lastc = c, c = c->next)
        if (c->remote == remote && c->pid == pid)
          break;

      if (c == 0)
        /* An unknown child died.
           Ignore it; it was inherited from our invoker.  */
        continue;

      DB (DB_JOBS, (child_failed
                    ? _("Reaping losing child 0x%08lx PID %ld %s\n")
                    : _("Reaping winning child 0x%08lx PID %ld %s\n"),
                    (unsigned long int) c, (long) c->pid,
                    c->remote ? _(" (remote)") : ""));

      if (c->sh_batch_file) {
        DB (DB_JOBS, (_("Cleaning up temp batch file %s\n"),
                      c->sh_batch_file));

        /* just try and remove, don't care if this fails */
        remove (c->sh_batch_file);

        /* all done with memory */
        free (c->sh_batch_file);
        c->sh_batch_file = NULL;
      }

      /* If this child had the good stdin, say it is now free.  */
      if (c->good_stdin)
        good_stdin_used = 0;

      if (child_failed && !c->noerror && !ignore_errors_flag)
        {
          /* The commands failed.  Write an error message,
             delete non-precious targets, and abort.  */
          static int delete_on_error = -1;
          child_error (c->file->name, exit_code, exit_sig, coredump, 0);
          c->file->update_status = 2;
          if (delete_on_error == -1)
            {
              struct file *f = lookup_file (".DELETE_ON_ERROR");
              delete_on_error = f != 0 && f->is_target;
            }
          if (exit_sig != 0 || delete_on_error)
            delete_child_targets (c);
        }
      else
        {
          if (child_failed)
            {
              /* The commands failed, but we don't care.  */
              child_error (c->file->name,
                           exit_code, exit_sig, coredump, 1);
              child_failed = 0;
            }

          /* If there are more commands to run, try to start them.  */
          if (job_next_command (c))
            {
              if (handling_fatal_signal)
                {
                  /* Never start new commands while we are dying.
                     Since there are more commands that wanted to be run,
                     the target was not completely remade.  So we treat
                     this as if a command had failed.  */
                  c->file->update_status = 2;
                }
              else
                {
                  /* Check again whether to start remotely.
                     Whether or not we want to changes over time.
                     Also, start_remote_job may need state set up
                     by start_remote_job_p.  */
                  c->remote = start_remote_job_p (0);
                  start_job_command (c);
                  /* Fatal signals are left blocked in case we were
                     about to put that child on the chain.  But it is
                     already there, so it is safe for a fatal signal to
                     arrive now; it will clean up this child's targets.  */
                  unblock_sigs ();
                  if (c->file->command_state == cs_running)
                    /* We successfully started the new command.
                       Loop to reap more children.  */
                    continue;
                }

              if (c->file->update_status != 0)
                /* We failed to start the commands.  */
                delete_child_targets (c);
            }
          else
            /* There are no more commands.  We got through them all
               without an unignored error.  Now the target has been
               successfully updated.  */
            c->file->update_status = 0;
        }

      /* When we get here, all the commands for C->file are finished
         (or aborted) and C->file->update_status contains 0 or 2.  But
         C->file->command_state is still cs_running if all the commands
         ran; notice_finish_file looks for cs_running to tell it that
         it's interesting to check the file's modtime again now.  */

      if (! handling_fatal_signal)
        /* Notice if the target of the commands has been changed.
           This also propagates its values for command_state and
           update_status to its also_make files.  */
        notice_finished_file (c->file);

      DB (DB_JOBS, (_("Removing child 0x%08lx PID %ld%s from chain.\n"),
                    (unsigned long int) c, (long) c->pid,
                    c->remote ? _(" (remote)") : ""));

      /* Block fatal signals while frobnicating the list, so that
         children and job_slots_used are always consistent.  Otherwise
         a fatal signal arriving after the child is off the chain and
         before job_slots_used is decremented would believe a child was
         live and call reap_children again.  */
      block_sigs ();

      /* There is now another slot open.  */
      if (job_slots_used > 0)
        --job_slots_used;

      /* Remove the child from the chain and free it.  */
      if (lastc == 0)
        children = c->next;
      else
        lastc->next = c->next;

      free_child (c);

      unblock_sigs ();

      /* If the job failed, and the -k flag was not given, die,
         unless we are already in the process of dying.  */
      if (!err && child_failed && !keep_going_flag &&
          /* fatal_error_signal will die with the right signal.  */
          !handling_fatal_signal)
        die (2);

      /* Only block for one child.  */
      block = 0;
    }

  return;
}


/* Free the storage allocated for CHILD.  */

static void
free_child (struct child *child)
{
  if (!jobserver_tokens)
    fatal (NILF, "INTERNAL: Freeing child 0x%08lx (%s) but no tokens left!\n",
           (unsigned long int) child, child->file->name);

  /* If we're using the jobserver and this child is not the only outstanding
     job, put a token back into the pipe for it.  */

  if (job_fds[1] >= 0 && jobserver_tokens > 1)
    {
      char token = '+';
      int r;

      /* Write a job token back to the pipe.  */

      EINTRLOOP (r, write (job_fds[1], &token, 1));
      if (r != 1)
        pfatal_with_name (_("write jobserver"));

      DB (DB_JOBS, (_("Released token for child 0x%08lx (%s).\n"),
                    (unsigned long int) child, child->file->name));
    }

  --jobserver_tokens;

  if (handling_fatal_signal) /* Don't bother free'ing if about to die.  */
    return;

  if (child->command_lines != 0)
    {
      register unsigned int i;
      for (i = 0; i < child->file->cmds->ncommand_lines; ++i)
        free (child->command_lines[i]);
      free ((char *) child->command_lines);
    }

  if (child->environment != 0)
    {
      register char **ep = child->environment;
      while (*ep != 0)
        free (*ep++);
      free ((char *) child->environment);
    }

  free ((char *) child);
}


#ifdef POSIX
extern sigset_t fatal_signal_set;
#endif

void
block_sigs (void)
{
#ifdef POSIX
  (void) sigprocmask (SIG_BLOCK, &fatal_signal_set, (sigset_t *) 0);
#else
# ifdef HAVE_SIGSETMASK
  (void) sigblock (fatal_signal_mask);
# endif
#endif
}

#ifdef POSIX
void
unblock_sigs (void)
{
  sigset_t empty;
  sigemptyset (&empty);
  sigprocmask (SIG_SETMASK, &empty, (sigset_t *) 0);
}
#endif

#ifdef MAKE_JOBSERVER
RETSIGTYPE
job_noop (int sig UNUSED)
{
}
/* Set the child handler action flags to FLAGS.  */
static void
set_child_handler_action_flags (int set_handler, int set_alarm)
{
  struct sigaction sa;

#ifdef __EMX__
  /* The child handler must be turned off here.  */
  signal (SIGCHLD, SIG_DFL);
#endif

  bzero ((char *) &sa, sizeof sa);
  sa.sa_handler = child_handler;
  sa.sa_flags = set_handler ? 0 : SA_RESTART;
#if defined SIGCHLD
  sigaction (SIGCHLD, &sa, NULL);
#endif
#if defined SIGCLD && SIGCLD != SIGCHLD
  sigaction (SIGCLD, &sa, NULL);
#endif
#if defined SIGALRM
  if (set_alarm)
    {
      /* If we're about to enter the read(), set an alarm to wake up in a
         second so we can check if the load has dropped and we can start more
         work.  On the way out, turn off the alarm and set SIG_DFL.  */
      alarm (set_handler ? 1 : 0);
      sa.sa_handler = set_handler ? job_noop : SIG_DFL;
      sa.sa_flags = 0;
      sigaction (SIGALRM, &sa, NULL);
    }
#endif
}
#endif


/* Start a job to run the commands specified in CHILD.
   CHILD is updated to reflect the commands and ID of the child process.

   NOTE: On return fatal signals are blocked!  The caller is responsible
   for calling `unblock_sigs', once the new child is safely on the chain so
   it can be cleaned up in the event of a fatal signal.  */

static void
start_job_command (struct child *child)
{
#ifndef _AMIGA
  static int bad_stdin = -1;
#endif
  register char *p;
  int flags;
#ifdef VMS
  char *argv;
#else
  char **argv;
#endif

  /* If we have a completely empty commandset, stop now.  */
  if (!child->command_ptr)
    goto next_command;

  /* Combine the flags parsed for the line itself with
     the flags specified globally for this target.  */
  flags = (child->file->command_flags
           | child->file->cmds->lines_flags[child->command_line - 1]);

  p = child->command_ptr;
  child->noerror = flags & COMMANDS_NOERROR;

  while (*p != '\0')
    {
      if (*p == '@')
        flags |= COMMANDS_SILENT;
      else if (*p == '+')
        flags |= COMMANDS_RECURSE;
      else if (*p == '-')
        child->noerror = 1;
      else if (!isblank ((unsigned char)*p))
        break;
      ++p;
    }

  /* Update the file's command flags with any new ones we found.  We only
     keep the COMMANDS_RECURSE setting.  Even this isn't 100% correct; we are
     now marking more commands recursive than should be in the case of
     multiline define/endef scripts where only one line is marked "+".  In
     order to really fix this, we'll have to keep a lines_flags for every
     actual line, after expansion.  */
  child->file->cmds->lines_flags[child->command_line - 1]
    |= flags & COMMANDS_RECURSE;

  /* Figure out an argument list from this command line.  */

  {
    char *end = 0;
#ifdef VMS
    argv = p;
#else
    argv = construct_command_argv (p, &end, child->file, &child->sh_batch_file);
#endif
    if (end == NULL)
      child->command_ptr = NULL;
    else
      {
        *end++ = '\0';
        child->command_ptr = end;
      }
  }

  /* If -q was given, say that updating `failed' if there was any text on the
     command line, or `succeeded' otherwise.  The exit status of 1 tells the
     user that -q is saying `something to do'; the exit status for a random
     error is 2.  */
  if (argv != 0 && question_flag && !(flags & COMMANDS_RECURSE))
    {
#ifndef VMS
      free (argv[0]);
      free ((char *) argv);
#endif
      child->file->update_status = 1;
      notice_finished_file (child->file);
      return;
    }

  if (touch_flag && !(flags & COMMANDS_RECURSE))
    {
      /* Go on to the next command.  It might be the recursive one.
         We construct ARGV only to find the end of the command line.  */
#ifndef VMS
      if (argv)
        {
          free (argv[0]);
          free ((char *) argv);
        }
#endif
      argv = 0;
    }

  if (argv == 0)
    {
    next_command:
#ifdef __MSDOS__
      execute_by_shell = 0;   /* in case construct_command_argv sets it */
#endif
      /* This line has no commands.  Go to the next.  */
      if (job_next_command (child))
        start_job_command (child);
      else
        {
          /* No more commands.  Make sure we're "running"; we might not be if
             (e.g.) all commands were skipped due to -n.  */
          set_command_state (child->file, cs_running);
          child->file->update_status = 0;
          notice_finished_file (child->file);
        }
      return;
    }

  /* Print out the command.  If silent, we call `message' with null so it
     can log the working directory before the command's own error messages
     appear.  */

  message (0, (just_print_flag || (!(flags & COMMANDS_SILENT) && !silent_flag))
           ? "%s" : (char *) 0, p);

  /* Tell update_goal_chain that a command has been started on behalf of
     this target.  It is important that this happens here and not in
     reap_children (where we used to do it), because reap_children might be
     reaping children from a different target.  We want this increment to
     guaranteedly indicate that a command was started for the dependency
     chain (i.e., update_file recursion chain) we are processing.  */

  ++commands_started;

  /* Optimize an empty command.  People use this for timestamp rules,
     so avoid forking a useless shell.  Do this after we increment
     commands_started so make still treats this special case as if it
     performed some action (makes a difference as to what messages are
     printed, etc.  */

#if !defined(VMS) && !defined(_AMIGA)
  if (
#if defined __MSDOS__ || defined (__EMX__)
      unixy_shell       /* the test is complicated and we already did it */
#else
      (argv[0] && !strcmp (argv[0], "/bin/sh"))
#endif
      && (argv[1]
          && argv[1][0] == '-' && argv[1][1] == 'c' && argv[1][2] == '\0')
      && (argv[2] && argv[2][0] == ':' && argv[2][1] == '\0')
      && argv[3] == NULL)
    {
      free (argv[0]);
      free ((char *) argv);
      goto next_command;
    }
#endif  /* !VMS && !_AMIGA */

  /* If -n was given, recurse to get the next line in the sequence.  */

  if (just_print_flag && !(flags & COMMANDS_RECURSE))
    {
#ifndef VMS
      free (argv[0]);
      free ((char *) argv);
#endif
      goto next_command;
    }

  /* Flush the output streams so they won't have things written twice.  */

  fflush (stdout);
  fflush (stderr);

#ifndef VMS
#if !defined(WINDOWS32) && !defined(_AMIGA) && !defined(__MSDOS__)

  /* Set up a bad standard input that reads from a broken pipe.  */

  if (bad_stdin == -1)
    {
      /* Make a file descriptor that is the read end of a broken pipe.
         This will be used for some children's standard inputs.  */
      int pd[2];
      if (pipe (pd) == 0)
        {
          /* Close the write side.  */
          (void) close (pd[1]);
          /* Save the read side.  */
          bad_stdin = pd[0];

          /* Set the descriptor to close on exec, so it does not litter any
             child's descriptor table.  When it is dup2'd onto descriptor 0,
             that descriptor will not close on exec.  */
          CLOSE_ON_EXEC (bad_stdin);
        }
    }

#endif /* !WINDOWS32 && !_AMIGA && !__MSDOS__ */

  /* Decide whether to give this child the `good' standard input
     (one that points to the terminal or whatever), or the `bad' one
     that points to the read side of a broken pipe.  */

  child->good_stdin = !good_stdin_used;
  if (child->good_stdin)
    good_stdin_used = 1;

#endif /* !VMS */

  child->deleted = 0;

#ifndef _AMIGA
  /* Set up the environment for the child.  */
  if (child->environment == 0)
    child->environment = target_environment (child->file);
#endif

#if !defined(__MSDOS__) && !defined(_AMIGA) && !defined(WINDOWS32)

#ifndef VMS
  /* start_waiting_job has set CHILD->remote if we can start a remote job.  */
  if (child->remote)
    {
      int is_remote, id, used_stdin;
      if (start_remote_job (argv, child->environment,
                            child->good_stdin ? 0 : bad_stdin,
                            &is_remote, &id, &used_stdin))
        /* Don't give up; remote execution may fail for various reasons.  If
           so, simply run the job locally.  */
        goto run_local;
      else
        {
          if (child->good_stdin && !used_stdin)
            {
              child->good_stdin = 0;
              good_stdin_used = 0;
            }
          child->remote = is_remote;
          child->pid = id;
        }
    }
  else
#endif /* !VMS */
    {
      /* Fork the child process.  */

      char **parent_environ;

    run_local:
      block_sigs ();

      child->remote = 0;

#ifdef VMS
      if (!child_execute_job (argv, child)) {
        /* Fork failed!  */
        perror_with_name ("vfork", "");
        goto error;
      }

#else

      parent_environ = environ;

# ifdef __EMX__
      /* If we aren't running a recursive command and we have a jobserver
         pipe, close it before exec'ing.  */
      if (!(flags & COMMANDS_RECURSE) && job_fds[0] >= 0)
        {
          CLOSE_ON_EXEC (job_fds[0]);
          CLOSE_ON_EXEC (job_fds[1]);
        }
      if (job_rfd >= 0)
        CLOSE_ON_EXEC (job_rfd);

      /* Never use fork()/exec() here! Use spawn() instead in exec_command() */
      child->pid = child_execute_job (child->good_stdin ? 0 : bad_stdin, 1,
                                      argv, child->environment);
      if (child->pid < 0)
        {
          /* spawn failed!  */
          unblock_sigs ();
          perror_with_name ("spawn", "");
          goto error;
        }

      /* undo CLOSE_ON_EXEC() after the child process has been started */
      if (!(flags & COMMANDS_RECURSE) && job_fds[0] >= 0)
        {
          fcntl (job_fds[0], F_SETFD, 0);
          fcntl (job_fds[1], F_SETFD, 0);
        }
      if (job_rfd >= 0)
        fcntl (job_rfd, F_SETFD, 0);

#else  /* !__EMX__ */

      child->pid = vfork ();
      environ = parent_environ; /* Restore value child may have clobbered.  */
      if (child->pid == 0)
        {
          /* We are the child side.  */
          unblock_sigs ();

          /* If we aren't running a recursive command and we have a jobserver
             pipe, close it before exec'ing.  */
          if (!(flags & COMMANDS_RECURSE) && job_fds[0] >= 0)
            {
              close (job_fds[0]);
              close (job_fds[1]);
            }
          if (job_rfd >= 0)
            close (job_rfd);

          child_execute_job (child->good_stdin ? 0 : bad_stdin, 1,
                             argv, child->environment);
        }
      else if (child->pid < 0)
        {
          /* Fork failed!  */
          unblock_sigs ();
          perror_with_name ("vfork", "");
          goto error;
        }
# endif  /* !__EMX__ */
#endif /* !VMS */
    }

#else   /* __MSDOS__ or Amiga or WINDOWS32 */
#ifdef __MSDOS__
  {
    int proc_return;

    block_sigs ();
    dos_status = 0;

    /* We call `system' to do the job of the SHELL, since stock DOS
       shell is too dumb.  Our `system' knows how to handle long
       command lines even if pipes/redirection is needed; it will only
       call COMMAND.COM when its internal commands are used.  */
    if (execute_by_shell)
      {
        char *cmdline = argv[0];
        /* We don't have a way to pass environment to `system',
           so we need to save and restore ours, sigh...  */
        char **parent_environ = environ;

        environ = child->environment;

        /* If we have a *real* shell, tell `system' to call
           it to do everything for us.  */
        if (unixy_shell)
          {
            /* A *real* shell on MSDOS may not support long
               command lines the DJGPP way, so we must use `system'.  */
            cmdline = argv[2];  /* get past "shell -c" */
          }

        dos_command_running = 1;
        proc_return = system (cmdline);
        environ = parent_environ;
        execute_by_shell = 0;   /* for the next time */
      }
    else
      {
        dos_command_running = 1;
        proc_return = spawnvpe (P_WAIT, argv[0], argv, child->environment);
      }

    /* Need to unblock signals before turning off
       dos_command_running, so that child's signals
       will be treated as such (see fatal_error_signal).  */
    unblock_sigs ();
    dos_command_running = 0;

    /* If the child got a signal, dos_status has its
       high 8 bits set, so be careful not to alter them.  */
    if (proc_return == -1)
      dos_status |= 0xff;
    else
      dos_status |= (proc_return & 0xff);
    ++dead_children;
    child->pid = dos_pid++;
  }
#endif /* __MSDOS__ */
#ifdef _AMIGA
  amiga_status = MyExecute (argv);

  ++dead_children;
  child->pid = amiga_pid++;
  if (amiga_batch_file)
  {
     amiga_batch_file = 0;
     DeleteFile (amiga_bname);        /* Ignore errors.  */
  }
#endif  /* Amiga */
#ifdef WINDOWS32
  {
      HANDLE hPID;
      char* arg0;

      /* make UNC paths safe for CreateProcess -- backslash format */
      arg0 = argv[0];
      if (arg0 && arg0[0] == '/' && arg0[1] == '/')
        for ( ; arg0 && *arg0; arg0++)
          if (*arg0 == '/')
            *arg0 = '\\';

      /* make sure CreateProcess() has Path it needs */
      sync_Path_environment();

      hPID = process_easy(argv, child->environment);

      if (hPID != INVALID_HANDLE_VALUE)
        child->pid = (int) hPID;
      else {
        int i;
        unblock_sigs();
        fprintf(stderr,
          _("process_easy() failed failed to launch process (e=%d)\n"),
          process_last_err(hPID));
               for (i = 0; argv[i]; i++)
                 fprintf(stderr, "%s ", argv[i]);
               fprintf(stderr, _("\nCounted %d args in failed launch\n"), i);
      }
  }
#endif /* WINDOWS32 */
#endif  /* __MSDOS__ or Amiga or WINDOWS32 */

  /* Bump the number of jobs started in this second.  */
  ++job_counter;

  /* We are the parent side.  Set the state to
     say the commands are running and return.  */

  set_command_state (child->file, cs_running);

  /* Free the storage used by the child's argument list.  */
#ifndef VMS
  free (argv[0]);
  free ((char *) argv);
#endif

  return;

 error:
  child->file->update_status = 2;
  notice_finished_file (child->file);
  return;
}

/* Try to start a child running.
   Returns nonzero if the child was started (and maybe finished), or zero if
   the load was too high and the child was put on the `waiting_jobs' chain.  */

static int
start_waiting_job (struct child *c)
{
  struct file *f = c->file;

  /* If we can start a job remotely, we always want to, and don't care about
     the local load average.  We record that the job should be started
     remotely in C->remote for start_job_command to test.  */

  c->remote = start_remote_job_p (1);

  /* If we are running at least one job already and the load average
     is too high, make this one wait.  */
  if (!c->remote && job_slots_used > 0 && load_too_high ())
    {
      /* Put this child on the chain of children waiting for the load average
         to go down.  */
      set_command_state (f, cs_running);
      c->next = waiting_jobs;
      waiting_jobs = c;
      return 0;
    }

  /* Start the first command; reap_children will run later command lines.  */
  start_job_command (c);

  switch (f->command_state)
    {
    case cs_running:
      c->next = children;
      DB (DB_JOBS, (_("Putting child 0x%08lx (%s) PID %ld%s on the chain.\n"),
                    (unsigned long int) c, c->file->name,
                    (long) c->pid, c->remote ? _(" (remote)") : ""));
      children = c;
      /* One more job slot is in use.  */
      ++job_slots_used;
      unblock_sigs ();
      break;

    case cs_not_started:
      /* All the command lines turned out to be empty.  */
      f->update_status = 0;
      /* FALLTHROUGH */

    case cs_finished:
      notice_finished_file (f);
      free_child (c);
      break;

    default:
      assert (f->command_state == cs_finished);
      break;
    }

  return 1;
}

/* Create a `struct child' for FILE and start its commands running.  */

void
new_job (struct file *file)
{
  register struct commands *cmds = file->cmds;
  register struct child *c;
  char **lines;
  register unsigned int i;

  /* Let any previously decided-upon jobs that are waiting
     for the load to go down start before this new one.  */
  start_waiting_jobs ();

  /* Reap any children that might have finished recently.  */
  reap_children (0, 0);

  /* Chop the commands up into lines if they aren't already.  */
  chop_commands (cmds);

  /* Expand the command lines and store the results in LINES.  */
  lines = (char **) xmalloc (cmds->ncommand_lines * sizeof (char *));
  for (i = 0; i < cmds->ncommand_lines; ++i)
    {
      /* Collapse backslash-newline combinations that are inside variable
         or function references.  These are left alone by the parser so
         that they will appear in the echoing of commands (where they look
         nice); and collapsed by construct_command_argv when it tokenizes.
         But letting them survive inside function invocations loses because
         we don't want the functions to see them as part of the text.  */

      char *in, *out, *ref;

      /* IN points to where in the line we are scanning.
         OUT points to where in the line we are writing.
         When we collapse a backslash-newline combination,
         IN gets ahead of OUT.  */

      in = out = cmds->command_lines[i];
      while ((ref = strchr (in, '$')) != 0)
        {
          ++ref;                /* Move past the $.  */

          if (out != in)
            /* Copy the text between the end of the last chunk
               we processed (where IN points) and the new chunk
               we are about to process (where REF points).  */
            bcopy (in, out, ref - in);

          /* Move both pointers past the boring stuff.  */
          out += ref - in;
          in = ref;

          if (*ref == '(' || *ref == '{')
            {
              char openparen = *ref;
              char closeparen = openparen == '(' ? ')' : '}';
              int count;
              char *p;

              *out++ = *in++;   /* Copy OPENPAREN.  */
              /* IN now points past the opening paren or brace.
                 Count parens or braces until it is matched.  */
              count = 0;
              while (*in != '\0')
                {
                  if (*in == closeparen && --count < 0)
                    break;
                  else if (*in == '\\' && in[1] == '\n')
                    {
                      /* We have found a backslash-newline inside a
                         variable or function reference.  Eat it and
                         any following whitespace.  */

                      int quoted = 0;
                      for (p = in - 1; p > ref && *p == '\\'; --p)
                        quoted = !quoted;

                      if (quoted)
                        /* There were two or more backslashes, so this is
                           not really a continuation line.  We don't collapse
                           the quoting backslashes here as is done in
                           collapse_continuations, because the line will
                           be collapsed again after expansion.  */
                        *out++ = *in++;
                      else
                        {
                          /* Skip the backslash, newline and
                             any following whitespace.  */
                          in = next_token (in + 2);

                          /* Discard any preceding whitespace that has
                             already been written to the output.  */
                          while (out > ref
                                 && isblank ((unsigned char)out[-1]))
                            --out;

                          /* Replace it all with a single space.  */
                          *out++ = ' ';
                        }
                    }
                  else
                    {
                      if (*in == openparen)
                        ++count;

                      *out++ = *in++;
                    }
                }
            }
        }

      /* There are no more references in this line to worry about.
         Copy the remaining uninteresting text to the output.  */
      if (out != in)
        strcpy (out, in);

      /* Finally, expand the line.  */
      lines[i] = allocated_variable_expand_for_file (cmds->command_lines[i],
                                                     file);
    }

  /* Start the command sequence, record it in a new
     `struct child', and add that to the chain.  */

  c = (struct child *) xmalloc (sizeof (struct child));
  bzero ((char *)c, sizeof (struct child));
  c->file = file;
  c->command_lines = lines;
  c->sh_batch_file = NULL;

  /* Fetch the first command line to be run.  */
  job_next_command (c);

  /* Wait for a job slot to be freed up.  If we allow an infinite number
     don't bother; also job_slots will == 0 if we're using the jobserver.  */

  if (job_slots != 0)
    while (job_slots_used == job_slots)
      reap_children (1, 0);

#ifdef MAKE_JOBSERVER
  /* If we are controlling multiple jobs make sure we have a token before
     starting the child. */

  /* This can be inefficient.  There's a decent chance that this job won't
     actually have to run any subprocesses: the command script may be empty
     or otherwise optimized away.  It would be nice if we could defer
     obtaining a token until just before we need it, in start_job_command.
     To do that we'd need to keep track of whether we'd already obtained a
     token (since start_job_command is called for each line of the job, not
     just once).  Also more thought needs to go into the entire algorithm;
     this is where the old parallel job code waits, so...  */

  else if (job_fds[0] >= 0)
    while (1)
      {
        char token;
        int got_token;
        int saved_errno;

        DB (DB_JOBS, ("Need a job token; we %shave children\n",
                      children ? "" : "don't "));

        /* If we don't already have a job started, use our "free" token.  */
        if (!jobserver_tokens)
          break;

        /* Read a token.  As long as there's no token available we'll block.
           We enable interruptible system calls before the read(2) so that if
           we get a SIGCHLD while we're waiting, we'll return with EINTR and
           we can process the death(s) and return tokens to the free pool.

           Once we return from the read, we immediately reinstate restartable
           system calls.  This allows us to not worry about checking for
           EINTR on all the other system calls in the program.

           There is one other twist: there is a span between the time
           reap_children() does its last check for dead children and the time
           the read(2) call is entered, below, where if a child dies we won't
           notice.  This is extremely serious as it could cause us to
           deadlock, given the right set of events.

           To avoid this, we do the following: before we reap_children(), we
           dup(2) the read FD on the jobserver pipe.  The read(2) call below
           uses that new FD.  In the signal handler, we close that FD.  That
           way, if a child dies during the section mentioned above, the
           read(2) will be invoked with an invalid FD and will return
           immediately with EBADF.  */

        /* Make sure we have a dup'd FD.  */
        if (job_rfd < 0)
          {
            DB (DB_JOBS, ("Duplicate the job FD\n"));
            job_rfd = dup (job_fds[0]);
          }

        /* Reap anything that's currently waiting.  */
        reap_children (0, 0);

        /* Kick off any jobs we have waiting for an opportunity that
           can run now (ie waiting for load). */
        start_waiting_jobs ();

        /* If our "free" slot has become available, use it; we don't need an
           actual token.  */
        if (!jobserver_tokens)
          break;

        /* There must be at least one child already, or we have no business
           waiting for a token. */
        if (!children)
          fatal (NILF, "INTERNAL: no children as we go to sleep on read\n");

        /* Set interruptible system calls, and read() for a job token.  */
        set_child_handler_action_flags (1, waiting_jobs != NULL);
        got_token = read (job_rfd, &token, 1);
        saved_errno = errno;
        set_child_handler_action_flags (0, waiting_jobs != NULL);

        /* If we got one, we're done here.  */
        if (got_token == 1)
          {
            DB (DB_JOBS, (_("Obtained token for child 0x%08lx (%s).\n"),
                          (unsigned long int) c, c->file->name));
            break;
          }

        /* If the error _wasn't_ expected (EINTR or EBADF), punt.  Otherwise,
           go back and reap_children(), and try again.  */
        errno = saved_errno;
        if (errno != EINTR && errno != EBADF)
          pfatal_with_name (_("read jobs pipe"));
        if (errno == EBADF)
          DB (DB_JOBS, ("Read returned EBADF.\n"));
      }
#endif

  ++jobserver_tokens;

  /* The job is now primed.  Start it running.
     (This will notice if there are in fact no commands.)  */
  (void) start_waiting_job (c);

  if (job_slots == 1 || not_parallel)
    /* Since there is only one job slot, make things run linearly.
       Wait for the child to die, setting the state to `cs_finished'.  */
    while (file->command_state == cs_running)
      reap_children (1, 0);

  return;
}


/* Move CHILD's pointers to the next command for it to execute.
   Returns nonzero if there is another command.  */

static int
job_next_command (struct child *child)
{
  while (child->command_ptr == 0 || *child->command_ptr == '\0')
    {
      /* There are no more lines in the expansion of this line.  */
      if (child->command_line == child->file->cmds->ncommand_lines)
        {
          /* There are no more lines to be expanded.  */
          child->command_ptr = 0;
          return 0;
        }
      else
        /* Get the next line to run.  */
        child->command_ptr = child->command_lines[child->command_line++];
    }
  return 1;
}

/* Determine if the load average on the system is too high to start a new job.
   The real system load average is only recomputed once a second.  However, a
   very parallel make can easily start tens or even hundreds of jobs in a
   second, which brings the system to its knees for a while until that first
   batch of jobs clears out.

   To avoid this we use a weighted algorithm to try to account for jobs which
   have been started since the last second, and guess what the load average
   would be now if it were computed.

   This algorithm was provided by Thomas Riedl <thomas.riedl@siemens.com>,
   who writes:

!      calculate something load-oid and add to the observed sys.load,
!      so that latter can catch up:
!      - every job started increases jobctr;
!      - every dying job decreases a positive jobctr;
!      - the jobctr value gets zeroed every change of seconds,
!        after its value*weight_b is stored into the 'backlog' value last_sec
!      - weight_a times the sum of jobctr and last_sec gets
!        added to the observed sys.load.
!
!      The two weights have been tried out on 24 and 48 proc. Sun Solaris-9
!      machines, using a several-thousand-jobs-mix of cpp, cc, cxx and smallish
!      sub-shelled commands (rm, echo, sed...) for tests.
!      lowering the 'direct influence' factor weight_a (e.g. to 0.1)
!      resulted in significant excession of the load limit, raising it
!      (e.g. to 0.5) took bad to small, fast-executing jobs and didn't
!      reach the limit in most test cases.
!
!      lowering the 'history influence' weight_b (e.g. to 0.1) resulted in
!      exceeding the limit for longer-running stuff (compile jobs in
!      the .5 to 1.5 sec. range),raising it (e.g. to 0.5) overrepresented
!      small jobs' effects.

 */

#define LOAD_WEIGHT_A           0.25
#define LOAD_WEIGHT_B           0.25

static int
load_too_high (void)
{
#if defined(__MSDOS__) || defined(VMS) || defined(_AMIGA) || defined(__riscos__)
  return 1;
#else
  static double last_sec;
  static time_t last_now;
  double load, guess;
  time_t now;

  if (max_load_average < 0)
    return 0;

  /* Find the real system load average.  */
  make_access ();
  if (getloadavg (&load, 1) != 1)
    {
      static int lossage = -1;
      /* Complain only once for the same error.  */
      if (lossage == -1 || errno != lossage)
        {
          if (errno == 0)
            /* An errno value of zero means getloadavg is just unsupported.  */
            error (NILF,
                   _("cannot enforce load limits on this operating system"));
          else
            perror_with_name (_("cannot enforce load limit: "), "getloadavg");
        }
      lossage = errno;
      load = 0;
    }
  user_access ();

  /* If we're in a new second zero the counter and correct the backlog
     value.  Only keep the backlog for one extra second; after that it's 0.  */
  now = time (NULL);
  if (last_now < now)
    {
      if (last_now == now - 1)
        last_sec = LOAD_WEIGHT_B * job_counter;
      else
        last_sec = 0.0;

      job_counter = 0;
      last_now = now;
    }

  /* Try to guess what the load would be right now.  */
  guess = load + (LOAD_WEIGHT_A * (job_counter + last_sec));

  DB (DB_JOBS, ("Estimated system load = %f (actual = %f) (max requested = %f)\n",
                guess, load, max_load_average));

  return guess >= max_load_average;
#endif
}

/* Start jobs that are waiting for the load to be lower.  */

void
start_waiting_jobs (void)
{
  struct child *job;

  if (waiting_jobs == 0)
    return;

  do
    {
      /* Check for recently deceased descendants.  */
      reap_children (0, 0);

      /* Take a job off the waiting list.  */
      job = waiting_jobs;
      waiting_jobs = job->next;

      /* Try to start that job.  We break out of the loop as soon
         as start_waiting_job puts one back on the waiting list.  */
    }
  while (start_waiting_job (job) && waiting_jobs != 0);

  return;
}


#ifndef WINDOWS32

/* EMX: Start a child process. This function returns the new pid.  */
# if defined __MSDOS__ || defined __EMX__
int
child_execute_job (int stdin_fd, int stdout_fd, char **argv, char **envp)
{
  int pid;
  /* stdin_fd == 0 means: nothing to do for stdin;
     stdout_fd == 1 means: nothing to do for stdout */
  int save_stdin = (stdin_fd != 0) ? dup (0) : 0;
  int save_stdout = (stdout_fd != 1) ? dup (1): 1;

  /* < 0 only if dup() failed */
  if (save_stdin < 0)
    fatal (NILF, _("no more file handles: could not duplicate stdin\n"));
  if (save_stdout < 0)
    fatal (NILF, _("no more file handles: could not duplicate stdout\n"));

  /* Close unnecessary file handles for the child.  */
  if (save_stdin != 0)
    CLOSE_ON_EXEC (save_stdin);
  if (save_stdout != 1)
    CLOSE_ON_EXEC (save_stdout);

  /* Connect the pipes to the child process.  */
  if (stdin_fd != 0)
    (void) dup2 (stdin_fd, 0);
  if (stdout_fd != 1)
    (void) dup2 (stdout_fd, 1);

  /* stdin_fd and stdout_fd must be closed on exit because we are
     still in the parent process */
  if (stdin_fd != 0)
    CLOSE_ON_EXEC (stdin_fd);
  if (stdout_fd != 1)
    CLOSE_ON_EXEC (stdout_fd);

  /* Run the command.  */
  pid = exec_command (argv, envp);

  /* Restore stdout/stdin of the parent and close temporary FDs.  */
  if (stdin_fd != 0)
    {
      if (dup2 (save_stdin, 0) != 0)
        fatal (NILF, _("Could not restore stdin\n"));
      else
        close (save_stdin);
    }

  if (stdout_fd != 1)
    {
      if (dup2 (save_stdout, 1) != 1)
        fatal (NILF, _("Could not restore stdout\n"));
      else
        close (save_stdout);
    }

  return pid;
}

#elif !defined (_AMIGA) && !defined (__MSDOS__)

/* UNIX:
   Replace the current process with one executing the command in ARGV.
   STDIN_FD and STDOUT_FD are used as the process's stdin and stdout; ENVP is
   the environment of the new program.  This function does not return.  */
void
child_execute_job (int stdin_fd, int stdout_fd, char **argv, char **envp)
{
  if (stdin_fd != 0)
    (void) dup2 (stdin_fd, 0);
  if (stdout_fd != 1)
    (void) dup2 (stdout_fd, 1);
  if (stdin_fd != 0)
    (void) close (stdin_fd);
  if (stdout_fd != 1)
    (void) close (stdout_fd);

  /* Run the command.  */
  exec_command (argv, envp);
}
#endif /* !AMIGA && !__MSDOS__ */
#endif /* !WINDOWS32 */


#ifndef _AMIGA
/* Replace the current process with one running the command in ARGV,
   with environment ENVP.  This function does not return.  */

/* EMX: This function returns the pid of the child process.  */
# ifdef __EMX__
int
# else
void
# endif
exec_command (char **argv, char **envp)
{
#ifdef VMS
  /* to work around a problem with signals and execve: ignore them */
#ifdef SIGCHLD
  signal (SIGCHLD,SIG_IGN);
#endif
  /* Run the program.  */
  execve (argv[0], argv, envp);
  perror_with_name ("execve: ", argv[0]);
  _exit (EXIT_FAILURE);
#else
#ifdef WINDOWS32
  HANDLE hPID;
  HANDLE hWaitPID;
  int err = 0;
  int exit_code = EXIT_FAILURE;

  /* make sure CreateProcess() has Path it needs */
  sync_Path_environment();

  /* launch command */
  hPID = process_easy(argv, envp);

  /* make sure launch ok */
  if (hPID == INVALID_HANDLE_VALUE)
    {
      int i;
      fprintf(stderr,
              _("process_easy() failed failed to launch process (e=%d)\n"),
              process_last_err(hPID));
      for (i = 0; argv[i]; i++)
          fprintf(stderr, "%s ", argv[i]);
      fprintf(stderr, _("\nCounted %d args in failed launch\n"), i);
      exit(EXIT_FAILURE);
    }

  /* wait and reap last child */
  hWaitPID = process_wait_for_any();
  while (hWaitPID)
    {
      /* was an error found on this process? */
      err = process_last_err(hWaitPID);

      /* get exit data */
      exit_code = process_exit_code(hWaitPID);

      if (err)
          fprintf(stderr, "make (e=%d, rc=%d): %s",
                  err, exit_code, map_windows32_error_to_string(err));

      /* cleanup process */
      process_cleanup(hWaitPID);

      /* expect to find only last pid, warn about other pids reaped */
      if (hWaitPID == hPID)
          break;
      else
          fprintf(stderr,
                  _("make reaped child pid %d, still waiting for pid %d\n"),
                  hWaitPID, hPID);
    }

  /* return child's exit code as our exit code */
  exit(exit_code);

#else  /* !WINDOWS32 */

# ifdef __EMX__
  int pid;
# endif

  /* Be the user, permanently.  */
  child_access ();

# ifdef __EMX__

  /* Run the program.  */
  pid = spawnvpe (P_NOWAIT, argv[0], argv, envp);

  if (pid >= 0)
    return pid;

  /* the file might have a strange shell extension */
  if (errno == ENOENT)
    errno = ENOEXEC;

# else

  /* Run the program.  */
  environ = envp;
  execvp (argv[0], argv);

# endif /* !__EMX__ */

  switch (errno)
    {
    case ENOENT:
      error (NILF, _("%s: Command not found"), argv[0]);
      break;
    case ENOEXEC:
      {
        /* The file is not executable.  Try it as a shell script.  */
        extern char *getenv ();
        char *shell;
        char **new_argv;
        int argc;
        int i=1;

# ifdef __EMX__
        /* Do not use $SHELL from the environment */
        struct variable *p = lookup_variable ("SHELL", 5);
        if (p)
          shell = p->value;
        else
          shell = 0;
# else
        shell = getenv ("SHELL");
# endif
        if (shell == 0)
          shell = default_shell;

        argc = 1;
        while (argv[argc] != 0)
          ++argc;

# ifdef __EMX__
        if (!unixy_shell)
          ++argc;
# endif

        new_argv = (char **) alloca ((1 + argc + 1) * sizeof (char *));
        new_argv[0] = shell;

# ifdef __EMX__
        if (!unixy_shell)
          {
            new_argv[1] = "/c";
            ++i;
            --argc;
          }
# endif

        new_argv[i] = argv[0];
        while (argc > 0)
          {
            new_argv[i + argc] = argv[argc];
            --argc;
          }

# ifdef __EMX__
        pid = spawnvpe (P_NOWAIT, shell, new_argv, envp);
        if (pid >= 0)
          break;
# else
        execvp (shell, new_argv);
# endif
        if (errno == ENOENT)
          error (NILF, _("%s: Shell program not found"), shell);
        else
          perror_with_name ("execvp: ", shell);
        break;
      }

# ifdef __EMX__
    case EINVAL:
      /* this nasty error was driving me nuts :-( */
      error (NILF, _("spawnvpe: environment space might be exhausted"));
      /* FALLTHROUGH */
# endif

    default:
      perror_with_name ("execvp: ", argv[0]);
      break;
    }

# ifdef __EMX__
  return pid;
# else
  _exit (127);
# endif
#endif /* !WINDOWS32 */
#endif /* !VMS */
}
#else /* On Amiga */
void exec_command (char **argv)
{
  MyExecute (argv);
}

void clean_tmp (void)
{
  DeleteFile (amiga_bname);
}

#endif /* On Amiga */


#ifndef VMS
/* Figure out the argument list necessary to run LINE as a command.  Try to
   avoid using a shell.  This routine handles only ' quoting, and " quoting
   when no backslash, $ or ` characters are seen in the quotes.  Starting
   quotes may be escaped with a backslash.  If any of the characters in
   sh_chars[] is seen, or any of the builtin commands listed in sh_cmds[]
   is the first word of a line, the shell is used.

   If RESTP is not NULL, *RESTP is set to point to the first newline in LINE.
   If *RESTP is NULL, newlines will be ignored.

   SHELL is the shell to use, or nil to use the default shell.
   IFS is the value of $IFS, or nil (meaning the default).  */

static char **
construct_command_argv_internal (char *line, char **restp, char *shell,
                                 char *ifs, char **batch_filename_ptr)
{
#ifdef __MSDOS__
  /* MSDOS supports both the stock DOS shell and ports of Unixy shells.
     We call `system' for anything that requires ``slow'' processing,
     because DOS shells are too dumb.  When $SHELL points to a real
     (unix-style) shell, `system' just calls it to do everything.  When
     $SHELL points to a DOS shell, `system' does most of the work
     internally, calling the shell only for its internal commands.
     However, it looks on the $PATH first, so you can e.g. have an
     external command named `mkdir'.

     Since we call `system', certain characters and commands below are
     actually not specific to COMMAND.COM, but to the DJGPP implementation
     of `system'.  In particular:

       The shell wildcard characters are in DOS_CHARS because they will
       not be expanded if we call the child via `spawnXX'.

       The `;' is in DOS_CHARS, because our `system' knows how to run
       multiple commands on a single line.

       DOS_CHARS also include characters special to 4DOS/NDOS, so we
       won't have to tell one from another and have one more set of
       commands and special characters.  */
  static char sh_chars_dos[] = "*?[];|<>%^&()";
  static char *sh_cmds_dos[] = { "break", "call", "cd", "chcp", "chdir", "cls",
                                 "copy", "ctty", "date", "del", "dir", "echo",
                                 "erase", "exit", "for", "goto", "if", "md",
                                 "mkdir", "path", "pause", "prompt", "rd",
                                 "rmdir", "rem", "ren", "rename", "set",
                                 "shift", "time", "type", "ver", "verify",
                                 "vol", ":", 0 };

  static char sh_chars_sh[]  = "#;\"*?[]&|<>(){}$`^";
  static char *sh_cmds_sh[]  = { "cd", "echo", "eval", "exec", "exit", "login",
                                 "logout", "set", "umask", "wait", "while",
                                 "for", "case", "if", ":", ".", "break",
                                 "continue", "export", "read", "readonly",
                                 "shift", "times", "trap", "switch", "unset",
                                 0 };

  char *sh_chars;
  char **sh_cmds;
#elif defined (__EMX__)
  static char sh_chars_dos[] = "*?[];|<>%^&()";
  static char *sh_cmds_dos[] = { "break", "call", "cd", "chcp", "chdir", "cls",
                                 "copy", "ctty", "date", "del", "dir", "echo",
                                 "erase", "exit", "for", "goto", "if", "md",
                                 "mkdir", "path", "pause", "prompt", "rd",
                                 "rmdir", "rem", "ren", "rename", "set",
                                 "shift", "time", "type", "ver", "verify",
                                 "vol", ":", 0 };

  static char sh_chars_os2[] = "*?[];|<>%^()\"'&";
  static char *sh_cmds_os2[] = { "call", "cd", "chcp", "chdir", "cls", "copy",
                             "date", "del", "detach", "dir", "echo",
                             "endlocal", "erase", "exit", "for", "goto", "if",
                             "keys", "md", "mkdir", "move", "path", "pause",
                             "prompt", "rd", "rem", "ren", "rename", "rmdir",
                             "set", "setlocal", "shift", "start", "time",
                             "type", "ver", "verify", "vol", ":", 0 };

  static char sh_chars_sh[]  = "#;\"*?[]&|<>(){}$`^~'";
  static char *sh_cmds_sh[]  = { "echo", "cd", "eval", "exec", "exit", "login",
                                 "logout", "set", "umask", "wait", "while",
                                 "for", "case", "if", ":", ".", "break",
                                 "continue", "export", "read", "readonly",
                                 "shift", "times", "trap", "switch", "unset",
                                 0 };
  char *sh_chars;
  char **sh_cmds;

#elif defined (_AMIGA)
  static char sh_chars[] = "#;\"|<>()?*$`";
  static char *sh_cmds[] = { "cd", "eval", "if", "delete", "echo", "copy",
                             "rename", "set", "setenv", "date", "makedir",
                             "skip", "else", "endif", "path", "prompt",
                             "unset", "unsetenv", "version",
                             0 };
#elif defined (WINDOWS32)
  static char sh_chars_dos[] = "\"|&<>";
  static char *sh_cmds_dos[] = { "break", "call", "cd", "chcp", "chdir", "cls",
                             "copy", "ctty", "date", "del", "dir", "echo",
                             "erase", "exit", "for", "goto", "if", "if", "md",
                             "mkdir", "path", "pause", "prompt", "rd", "rem",
                             "ren", "rename", "rmdir", "set", "shift", "time",
                             "type", "ver", "verify", "vol", ":", 0 };
  static char sh_chars_sh[] = "#;\"*?[]&|<>(){}$`^";
  static char *sh_cmds_sh[] = { "cd", "eval", "exec", "exit", "login",
                             "logout", "set", "umask", "wait", "while", "for",
                             "case", "if", ":", ".", "break", "continue",
                             "export", "read", "readonly", "shift", "times",
                             "trap", "switch", "test",
#ifdef BATCH_MODE_ONLY_SHELL
                 "echo",
#endif
                 0 };
  char*  sh_chars;
  char** sh_cmds;
#elif defined(__riscos__)
  static char sh_chars[] = "";
  static char *sh_cmds[] = { 0 };
#else  /* must be UNIX-ish */
  static char sh_chars[] = "#;\"*?[]&|<>(){}$`^~!";
  static char *sh_cmds[] = { ".", ":", "break", "case", "cd", "continue",
                             "eval", "exec", "exit", "export", "for", "if",
                             "login", "logout", "read", "readonly", "set",
                             "shift", "switch", "test", "times", "trap",
                             "umask", "wait", "while", 0 };
#endif
  register int i;
  register char *p;
  register char *ap;
  char *end;
  int instring, word_has_equals, seen_nonequals, last_argument_was_empty;
  char **new_argv = 0;
#ifdef WINDOWS32
  int slow_flag = 0;

  if (no_default_sh_exe) {
    sh_cmds = sh_cmds_dos;
    sh_chars = sh_chars_dos;
  } else {
    sh_cmds = sh_cmds_sh;
    sh_chars = sh_chars_sh;
  }
#endif /* WINDOWS32 */

  if (restp != NULL)
    *restp = NULL;

  /* Make sure not to bother processing an empty line.  */
  while (isblank ((unsigned char)*line))
    ++line;
  if (*line == '\0')
    return 0;

  /* See if it is safe to parse commands internally.  */
  if (shell == 0)
    shell = default_shell;
#ifdef WINDOWS32
  else if (strcmp (shell, default_shell))
  {
    char *s1 = _fullpath(NULL, shell, 0);
    char *s2 = _fullpath(NULL, default_shell, 0);

    slow_flag = strcmp((s1 ? s1 : ""), (s2 ? s2 : ""));

    if (s1)
      free (s1);
    if (s2)
      free (s2);
  }
  if (slow_flag)
    goto slow;
#else  /* not WINDOWS32 */
#if defined (__MSDOS__) || defined (__EMX__)
  else if (stricmp (shell, default_shell))
    {
      extern int _is_unixy_shell (const char *_path);

      DB (DB_BASIC, (_("$SHELL changed (was `%s', now `%s')\n"),
                     default_shell, shell));
      unixy_shell = _is_unixy_shell (shell);
      /* we must allocate a copy of shell: construct_command_argv() will free
       * shell after this function returns.  */
      default_shell = xstrdup (shell);
    }
  if (unixy_shell)
    {
      sh_chars = sh_chars_sh;
      sh_cmds  = sh_cmds_sh;
    }
  else
    {
      sh_chars = sh_chars_dos;
      sh_cmds  = sh_cmds_dos;
# ifdef __EMX__
      if (_osmode == OS2_MODE)
        {
          sh_chars = sh_chars_os2;
          sh_cmds = sh_cmds_os2;
        }
# endif
    }
#else  /* !__MSDOS__ */
  else if (strcmp (shell, default_shell))
    goto slow;
#endif /* !__MSDOS__ && !__EMX__ */
#endif /* not WINDOWS32 */

  if (ifs != 0)
    for (ap = ifs; *ap != '\0'; ++ap)
      if (*ap != ' ' && *ap != '\t' && *ap != '\n')
        goto slow;

  i = strlen (line) + 1;

  /* More than 1 arg per character is impossible.  */
  new_argv = (char **) xmalloc (i * sizeof (char *));

  /* All the args can fit in a buffer as big as LINE is.   */
  ap = new_argv[0] = (char *) xmalloc (i);
  end = ap + i;

  /* I is how many complete arguments have been found.  */
  i = 0;
  instring = word_has_equals = seen_nonequals = last_argument_was_empty = 0;
  for (p = line; *p != '\0'; ++p)
    {
      if (ap > end)
        abort ();

      if (instring)
        {
        string_char:
          /* Inside a string, just copy any char except a closing quote
             or a backslash-newline combination.  */
          if (*p == instring)
            {
              instring = 0;
              if (ap == new_argv[0] || *(ap-1) == '\0')
                last_argument_was_empty = 1;
            }
          else if (*p == '\\' && p[1] == '\n')
            goto swallow_escaped_newline;
          else if (*p == '\n' && restp != NULL)
            {
              /* End of the command line.  */
              *restp = p;
              goto end_of_line;
            }
          /* Backslash, $, and ` are special inside double quotes.
             If we see any of those, punt.
             But on MSDOS, if we use COMMAND.COM, double and single
             quotes have the same effect.  */
          else if (instring == '"' && strchr ("\\$`", *p) != 0 && unixy_shell)
            goto slow;
          else
            *ap++ = *p;
        }
      else if (strchr (sh_chars, *p) != 0)
        /* Not inside a string, but it's a special char.  */
        goto slow;
#ifdef  __MSDOS__
      else if (*p == '.' && p[1] == '.' && p[2] == '.' && p[3] != '.')
        /* `...' is a wildcard in DJGPP.  */
        goto slow;
#endif
      else
        /* Not a special char.  */
        switch (*p)
          {
          case '=':
            /* Equals is a special character in leading words before the
               first word with no equals sign in it.  This is not the case
               with sh -k, but we never get here when using nonstandard
               shell flags.  */
            if (! seen_nonequals && unixy_shell)
              goto slow;
            word_has_equals = 1;
            *ap++ = '=';
            break;

          case '\\':
            /* Backslash-newline combinations are eaten.  */
            if (p[1] == '\n')
              {
              swallow_escaped_newline:

                /* Eat the backslash, the newline, and following whitespace,
                   replacing it all with a single space.  */
                p += 2;

                /* If there is a tab after a backslash-newline,
                   remove it from the source line which will be echoed,
                   since it was most likely used to line
                   up the continued line with the previous one.  */
                if (*p == '\t')
                  /* Note these overlap and strcpy() is undefined for
                     overlapping objects in ANSI C.  The strlen() _IS_ right,
                     since we need to copy the nul byte too.  */
                  bcopy (p + 1, p, strlen (p));

                if (instring)
                  goto string_char;
                else
                  {
                    if (ap != new_argv[i])
                      /* Treat this as a space, ending the arg.
                         But if it's at the beginning of the arg, it should
                         just get eaten, rather than becoming an empty arg. */
                      goto end_of_arg;
                    else
                      p = next_token (p) - 1;
                  }
              }
            else if (p[1] != '\0')
              {
#ifdef HAVE_DOS_PATHS
                /* Only remove backslashes before characters special
                   to Unixy shells.  All other backslashes are copied
                   verbatim, since they are probably DOS-style
                   directory separators.  This still leaves a small
                   window for problems, but at least it should work
                   for the vast majority of naive users.  */

#ifdef __MSDOS__
                /* A dot is only special as part of the "..."
                   wildcard.  */
                if (strneq (p + 1, ".\\.\\.", 5))
                  {
                    *ap++ = '.';
                    *ap++ = '.';
                    p += 4;
                  }
                else
#endif
                  if (p[1] != '\\' && p[1] != '\''
                      && !isspace ((unsigned char)p[1])
                      && (strchr (sh_chars_sh, p[1]) == 0))
                    /* back up one notch, to copy the backslash */
                    --p;
#endif  /* HAVE_DOS_PATHS */

                /* Copy and skip the following char.  */
                *ap++ = *++p;
              }
            break;

          case '\'':
          case '"':
            instring = *p;
            break;

          case '\n':
            if (restp != NULL)
              {
                /* End of the command line.  */
                *restp = p;
                goto end_of_line;
              }
            else
              /* Newlines are not special.  */
              *ap++ = '\n';
            break;

          case ' ':
          case '\t':
          end_of_arg:
            /* We have the end of an argument.
               Terminate the text of the argument.  */
            *ap++ = '\0';
            new_argv[++i] = ap;
            last_argument_was_empty = 0;

            /* Update SEEN_NONEQUALS, which tells us if every word
               heretofore has contained an `='.  */
            seen_nonequals |= ! word_has_equals;
            if (word_has_equals && ! seen_nonequals)
              /* An `=' in a word before the first
                 word without one is magical.  */
              goto slow;
            word_has_equals = 0; /* Prepare for the next word.  */

            /* If this argument is the command name,
               see if it is a built-in shell command.
               If so, have the shell handle it.  */
            if (i == 1)
              {
                register int j;
                for (j = 0; sh_cmds[j] != 0; ++j)
                  {
                    if (streq (sh_cmds[j], new_argv[0]))
                      goto slow;
# ifdef __EMX__
                    /* Non-Unix shells are case insensitive.  */
                    if (!unixy_shell
                        && strcasecmp (sh_cmds[j], new_argv[0]) == 0)
                      goto slow;
# endif
                  }
              }

            /* Ignore multiple whitespace chars.  */
            p = next_token (p);
            /* Next iteration should examine the first nonwhite char.  */
            --p;
            break;

          default:
            *ap++ = *p;
            break;
          }
    }
 end_of_line:

  if (instring)
    /* Let the shell deal with an unterminated quote.  */
    goto slow;

  /* Terminate the last argument and the argument list.  */

  *ap = '\0';
  if (new_argv[i][0] != '\0' || last_argument_was_empty)
    ++i;
  new_argv[i] = 0;

  if (i == 1)
    {
      register int j;
      for (j = 0; sh_cmds[j] != 0; ++j)
        if (streq (sh_cmds[j], new_argv[0]))
          goto slow;
    }

  if (new_argv[0] == 0)
    /* Line was empty.  */
    return 0;

  return new_argv;

 slow:;
  /* We must use the shell.  */

  if (new_argv != 0)
    {
      /* Free the old argument list we were working on.  */
      free (new_argv[0]);
      free ((void *)new_argv);
    }

#ifdef __MSDOS__
  execute_by_shell = 1; /* actually, call `system' if shell isn't unixy */
#endif

#ifdef _AMIGA
  {
    char *ptr;
    char *buffer;
    char *dptr;

    buffer = (char *)xmalloc (strlen (line)+1);

    ptr = line;
    for (dptr=buffer; *ptr; )
    {
      if (*ptr == '\\' && ptr[1] == '\n')
        ptr += 2;
      else if (*ptr == '@') /* Kludge: multiline commands */
      {
        ptr += 2;
        *dptr++ = '\n';
      }
      else
        *dptr++ = *ptr++;
    }
    *dptr = 0;

    new_argv = (char **) xmalloc (2 * sizeof (char *));
    new_argv[0] = buffer;
    new_argv[1] = 0;
  }
#else   /* Not Amiga  */
#ifdef WINDOWS32
  /*
   * Not eating this whitespace caused things like
   *
   *    sh -c "\n"
   *
   * which gave the shell fits. I think we have to eat
   * whitespace here, but this code should be considered
   * suspicious if things start failing....
   */

  /* Make sure not to bother processing an empty line.  */
  while (isspace ((unsigned char)*line))
    ++line;
  if (*line == '\0')
    return 0;
#endif /* WINDOWS32 */
  {
    /* SHELL may be a multi-word command.  Construct a command line
       "SHELL -c LINE", with all special chars in LINE escaped.
       Then recurse, expanding this command line to get the final
       argument list.  */

    unsigned int shell_len = strlen (shell);
#ifndef VMS
    static char minus_c[] = " -c ";
#else
    static char minus_c[] = "";
#endif
    unsigned int line_len = strlen (line);

    char *new_line = (char *) alloca (shell_len + (sizeof (minus_c) - 1)
                                      + (line_len * 2) + 1);
    char *command_ptr = NULL; /* used for batch_mode_shell mode */

# ifdef __EMX__ /* is this necessary? */
    if (!unixy_shell)
      minus_c[1] = '/'; /* " /c " */
# endif

    ap = new_line;
    bcopy (shell, ap, shell_len);
    ap += shell_len;
    bcopy (minus_c, ap, sizeof (minus_c) - 1);
    ap += sizeof (minus_c) - 1;
    command_ptr = ap;
    for (p = line; *p != '\0'; ++p)
      {
        if (restp != NULL && *p == '\n')
          {
            *restp = p;
            break;
          }
        else if (*p == '\\' && p[1] == '\n')
          {
            /* Eat the backslash, the newline, and following whitespace,
               replacing it all with a single space (which is escaped
               from the shell).  */
            p += 2;

            /* If there is a tab after a backslash-newline,
               remove it from the source line which will be echoed,
               since it was most likely used to line
               up the continued line with the previous one.  */
            if (*p == '\t')
              bcopy (p + 1, p, strlen (p));

            p = next_token (p);
            --p;
            if (unixy_shell && !batch_mode_shell)
              *ap++ = '\\';
            *ap++ = ' ';
            continue;
          }

        /* DOS shells don't know about backslash-escaping.  */
        if (unixy_shell && !batch_mode_shell &&
            (*p == '\\' || *p == '\'' || *p == '"'
             || isspace ((unsigned char)*p)
             || strchr (sh_chars, *p) != 0))
          *ap++ = '\\';
#ifdef __MSDOS__
        else if (unixy_shell && strneq (p, "...", 3))
          {
            /* The case of `...' wildcard again.  */
            strcpy (ap, "\\.\\.\\");
            ap += 5;
            p  += 2;
          }
#endif
        *ap++ = *p;
      }
    if (ap == new_line + shell_len + sizeof (minus_c) - 1)
      /* Line was empty.  */
      return 0;
    *ap = '\0';

#ifdef WINDOWS32
    /* Some shells do not work well when invoked as 'sh -c xxx' to run a
       command line (e.g. Cygnus GNUWIN32 sh.exe on WIN32 systems).  In these
       cases, run commands via a script file.  */
    if ((no_default_sh_exe || batch_mode_shell) && batch_filename_ptr) {
      FILE* batch = NULL;
      int id = GetCurrentProcessId();
      PATH_VAR(fbuf);

      /* create a file name */
      sprintf(fbuf, "make%d", id);
      *batch_filename_ptr = create_batch_filename (fbuf, unixy_shell);

      DB (DB_JOBS, (_("Creating temporary batch file %s\n"),
                    *batch_filename_ptr));

      /* create batch file to execute command */
      batch = fopen (*batch_filename_ptr, "w");
      if (!unixy_shell)
        fputs ("@echo off\n", batch);
      fputs (command_ptr, batch);
      fputc ('\n', batch);
      fclose (batch);

      /* create argv */
      new_argv = (char **) xmalloc(3 * sizeof (char *));
      if (unixy_shell) {
        new_argv[0] = xstrdup (shell);
        new_argv[1] = *batch_filename_ptr; /* only argv[0] gets freed later */
      } else {
        new_argv[0] = xstrdup (*batch_filename_ptr);
        new_argv[1] = NULL;
      }
      new_argv[2] = NULL;
    } else
#endif /* WINDOWS32 */
    if (unixy_shell)
      new_argv = construct_command_argv_internal (new_line, (char **) NULL,
                                                  (char *) 0, (char *) 0,
                                                  (char **) 0);
#ifdef __EMX__
    else if (!unixy_shell)
      {
        /* new_line is local, must not be freed therefore
           We use line here instead of new_line because we run the shell
           manually.  */
        size_t line_len = strlen (line);
        char *p = new_line;
        char *q = new_line;
        memcpy (new_line, line, line_len + 1);
        /* replace all backslash-newline combination and also following tabs */
        while (*q != '\0')
          {
            if (q[0] == '\\' && q[1] == '\n')
              {
                q += 2; /* remove '\\' and '\n' */
                if (q[0] == '\t')
                  q++; /* remove 1st tab in the next line */
              }
            else
              *p++ = *q++;
          }
        *p = '\0';

# ifndef NO_CMD_DEFAULT
        if (strnicmp (new_line, "echo", 4) == 0
            && (new_line[4] == ' ' || new_line[4] == '\t'))
          {
            /* the builtin echo command: handle it separately */
            size_t echo_len = line_len - 5;
            char *echo_line = new_line + 5;

            /* special case: echo 'x="y"'
               cmd works this way: a string is printed as is, i.e., no quotes
               are removed. But autoconf uses a command like echo 'x="y"' to
               determine whether make works. autoconf expects the output x="y"
               so we will do exactly that.
               Note: if we do not allow cmd to be the default shell
               we do not need this kind of voodoo */
            if (echo_line[0] == '\''
                && echo_line[echo_len - 1] == '\''
                && strncmp (echo_line + 1, "ac_maketemp=",
                            strlen ("ac_maketemp=")) == 0)
              {
                /* remove the enclosing quotes */
                memmove (echo_line, echo_line + 1, echo_len - 2);
                echo_line[echo_len - 2] = '\0';
              }
          }
# endif

        {
          /* Let the shell decide what to do. Put the command line into the
             2nd command line argument and hope for the best ;-)  */
          size_t sh_len = strlen (shell);

          /* exactly 3 arguments + NULL */
          new_argv = (char **) xmalloc (4 * sizeof (char *));
          /* Exactly strlen(shell) + strlen("/c") + strlen(line) + 3 times
             the trailing '\0' */
          new_argv[0] = (char *) malloc (sh_len + line_len + 5);
          memcpy (new_argv[0], shell, sh_len + 1);
          new_argv[1] = new_argv[0] + sh_len + 1;
          memcpy (new_argv[1], "/c", 3);
          new_argv[2] = new_argv[1] + 3;
          memcpy (new_argv[2], new_line, line_len + 1);
          new_argv[3] = NULL;
        }
      }
#elif defined(__MSDOS__)
    else
      {
        /* With MSDOS shells, we must construct the command line here
           instead of recursively calling ourselves, because we
           cannot backslash-escape the special characters (see above).  */
        new_argv = (char **) xmalloc (sizeof (char *));
        line_len = strlen (new_line) - shell_len - sizeof (minus_c) + 1;
        new_argv[0] = xmalloc (line_len + 1);
        strncpy (new_argv[0],
                 new_line + shell_len + sizeof (minus_c) - 1, line_len);
        new_argv[0][line_len] = '\0';
      }
#else
    else
      fatal (NILF, _("%s (line %d) Bad shell context (!unixy && !batch_mode_shell)\n"),
            __FILE__, __LINE__);
#endif
  }
#endif  /* ! AMIGA */

  return new_argv;
}
#endif /* !VMS */

/* Figure out the argument list necessary to run LINE as a command.  Try to
   avoid using a shell.  This routine handles only ' quoting, and " quoting
   when no backslash, $ or ` characters are seen in the quotes.  Starting
   quotes may be escaped with a backslash.  If any of the characters in
   sh_chars[] is seen, or any of the builtin commands listed in sh_cmds[]
   is the first word of a line, the shell is used.

   If RESTP is not NULL, *RESTP is set to point to the first newline in LINE.
   If *RESTP is NULL, newlines will be ignored.

   FILE is the target whose commands these are.  It is used for
   variable expansion for $(SHELL) and $(IFS).  */

char **
construct_command_argv (char *line, char **restp, struct file *file,
                        char **batch_filename_ptr)
{
  char *shell, *ifs;
  char **argv;

#ifdef VMS
  char *cptr;
  int argc;

  argc = 0;
  cptr = line;
  for (;;)
    {
      while ((*cptr != 0)
             && (isspace ((unsigned char)*cptr)))
        cptr++;
      if (*cptr == 0)
        break;
      while ((*cptr != 0)
             && (!isspace((unsigned char)*cptr)))
        cptr++;
      argc++;
    }

  argv = (char **)malloc (argc * sizeof (char *));
  if (argv == 0)
    abort ();

  cptr = line;
  argc = 0;
  for (;;)
    {
      while ((*cptr != 0)
             && (isspace ((unsigned char)*cptr)))
        cptr++;
      if (*cptr == 0)
        break;
      DB (DB_JOBS, ("argv[%d] = [%s]\n", argc, cptr));
      argv[argc++] = cptr;
      while ((*cptr != 0)
             && (!isspace((unsigned char)*cptr)))
        cptr++;
      if (*cptr != 0)
        *cptr++ = 0;
    }
#else
  {
    /* Turn off --warn-undefined-variables while we expand SHELL and IFS.  */
    int save = warn_undefined_variables_flag;
    warn_undefined_variables_flag = 0;

    shell = allocated_variable_expand_for_file ("$(SHELL)", file);
#ifdef WINDOWS32
    /*
     * Convert to forward slashes so that construct_command_argv_internal()
     * is not confused.
     */
    if (shell) {
      char *p = w32ify (shell, 0);
      strcpy (shell, p);
    }
#endif
#ifdef __EMX__
    {
      static const char *unixroot = NULL;
      static const char *last_shell = "";
      static int init = 0;
      if (init == 0)
        {
          unixroot = getenv ("UNIXROOT");
          /* unixroot must be NULL or not empty */
          if (unixroot && unixroot[0] == '\0') unixroot = NULL;
          init = 1;
        }

      /* if we have an unixroot drive and if shell is not default_shell
         (which means it's either cmd.exe or the test has already been
         performed) and if shell is an absolute path without drive letter,
         try whether it exists e.g.: if "/bin/sh" does not exist use
         "$UNIXROOT/bin/sh" instead.  */
      if (unixroot && shell && strcmp (shell, last_shell) != 0
          && (shell[0] == '/' || shell[0] == '\\'))
        {
          /* trying a new shell, check whether it exists */
          size_t size = strlen (shell);
          char *buf = xmalloc (size + 7);
          memcpy (buf, shell, size);
          memcpy (buf + size, ".exe", 5); /* including the trailing '\0' */
          if (access (shell, F_OK) != 0 && access (buf, F_OK) != 0)
            {
              /* try the same for the unixroot drive */
              memmove (buf + 2, buf, size + 5);
              buf[0] = unixroot[0];
              buf[1] = unixroot[1];
              if (access (buf, F_OK) == 0)
                /* we have found a shell! */
                /* free(shell); */
                shell = buf;
              else
                free (buf);
            }
          else
            free (buf);
        }
    }
#endif /* __EMX__ */

    ifs = allocated_variable_expand_for_file ("$(IFS)", file);

    warn_undefined_variables_flag = save;
  }

  argv = construct_command_argv_internal (line, restp, shell, ifs, batch_filename_ptr);

  free (shell);
  free (ifs);
#endif /* !VMS */
  return argv;
}


#if !defined(HAVE_DUP2) && !defined(_AMIGA)
int
dup2 (int old, int new)
{
  int fd;

  (void) close (new);
  fd = dup (old);
  if (fd != new)
    {
      (void) close (fd);
      errno = EMFILE;
      return -1;
    }

  return fd;
}
#endif /* !HAPE_DUP2 && !_AMIGA */

/* On VMS systems, include special VMS functions.  */

#ifdef VMS
#include "vmsjobs.c"
#endif