Revert recent change for Bug#8855.

As reported by Harald Hanche-Olsen in
<http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00445.html>
the change introduces a further bug, of creating lots of zombie
processes in some cases.  Further work is needed to come up with a
better fix for Bug#8855.

5 files changed, 154 insertions, 183 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 6c9893b2f4f..99abda8a884 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2012-11-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Revert recent change for Bug#8855.
+        As reported by Harald Hanche-Olsen in
+        <http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00445.html>
+        the change introduces a further bug, of creating lots of zombie
+        processes in some cases.  Further work is needed to come up with a
+        better fix for Bug#8855.
+
 2012-11-24  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (draw_glyphs): Don't draw in mouse face if mouse
diff --git a/src/process.c b/src/process.c
index c095d13293b..77e99ead01f 100644
--- a/src/process.c
+++ b/src/process.c
@@ -130,6 +130,14 @@ extern int sys_select (int, SELECT_TYPE *, SELECT_TYPE *, SELECT_TYPE *,
                        EMACS_TIME *, void *);
 #endif
 
+#ifndef WNOHANG
+# undef waitpid
+# define waitpid(pid, status, options) wait (status)
+#endif
+#ifndef WUNTRACED
+# define WUNTRACED 0
+#endif
+
 /* Work around GCC 4.7.0 bug with strict overflow checking; see
    <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52904>.
    These lines can be removed once the GCC bug is fixed.  */
@@ -787,8 +795,9 @@ get_process (register Lisp_Object name)
 #ifdef SIGCHLD
 /* Fdelete_process promises to immediately forget about the process, but in
    reality, Emacs needs to remember those processes until they have been
-   treated by the SIGCHLD handler and waitpid has been invoked on them;
-   otherwise they might fill up the kernel's process table.  */
+   treated by the SIGCHLD handler; otherwise this handler would consider the
+   process as being synchronous and say that the synchronous process is
+   dead.  */
 static Lisp_Object deleted_pid_list;
 #endif
 
@@ -1695,7 +1704,16 @@ create_process (Lisp_Object process, char **new_argv, Lisp_Object current_dir)
   if (inchannel > max_process_desc)
     max_process_desc = inchannel;
 
-  /* This may signal an error. */
+  /* Until we store the proper pid, enable the SIGCHLD handler
+     to recognize an unknown pid as standing for this process.
+     It is very important not to let this `marker' value stay
+     in the table after this function has returned; if it does
+     it might cause call-process to hang and subsequent asynchronous
+     processes to get their return values scrambled.  */
+  XPROCESS (process)->pid = -1;
+
+  /* This must be called after the above line because it may signal an
+     error. */
   setup_process_coding_systems (process);
 
   encoded_current_dir = ENCODE_FILE (current_dir);
@@ -1862,8 +1880,6 @@ create_process (Lisp_Object process, char **new_argv, Lisp_Object current_dir)
 #endif
 
   XPROCESS (process)->pid = pid;
-  if (0 <= pid)
-    XPROCESS (process)->alive = 1;
 
   /* Stop blocking signals in the parent.  */
 #ifdef SIGCHLD
@@ -6257,35 +6273,9 @@ process has been transmitted to the serial port.  */)
   return process;
 }
 
-/* If the status of the process DESIRED has changed, return true and
-   set *STATUS to its exit status; otherwise, return false.
-   If HAVE is nonnegative, assume that HAVE = waitpid (HAVE, STATUS, ...)
-   has already been invoked, and do not invoke waitpid again.  */
-
-static bool
-process_status_retrieved (pid_t desired, pid_t have, int *status)
-{
-  if (have < 0)
-    {
-      /* Invoke waitpid only with a known process ID; do not invoke
-         waitpid with a nonpositive argument.  Otherwise, Emacs might
-         reap an unwanted process by mistake.  For example, invoking
-         waitpid (-1, ...) can mess up glib by reaping glib's subprocesses,
-         so that another thread running glib won't find them.  */
-      do
-        have = waitpid (desired, status, WNOHANG | WUNTRACED);
-      while (have < 0 && errno == EINTR);
-    }
-
-  return have == desired;
-}
-
-/* If PID is nonnegative, the child process PID with wait status W has
-   changed its status; record this and return true.
-
-   If PID is negative, ignore W, and look for known child processes
-   of Emacs whose status have changed.  For each one found, record its new
-   status.
+/* On receipt of a signal that a child status has changed, loop asking
+   about children with changed statuses until the system says there
+   are no more.
 
    All we do is change the status; we do not run sentinels or print
    notifications.  That is saved for the next time keyboard input is
@@ -6308,15 +6298,13 @@ process_status_retrieved (pid_t desired, pid_t have, int *status)
    ** Malloc WARNING: This should never call malloc either directly or
    indirectly; if it does, that is a bug  */
 
+/* Record the changed status of the child process PID with wait status W.  */
 void
 record_child_status_change (pid_t pid, int w)
 {
 #ifdef SIGCHLD
-
-  /* On POSIXish hosts, record at most one child only if we already
-     know one child that has exited.  */
-  bool record_at_most_one_child = 0 <= pid;
-
+  Lisp_Object proc;
+  struct Lisp_Process *p;
   Lisp_Object tail;
 
   /* Find the process that signaled us, and record its status.  */
@@ -6324,69 +6312,68 @@ record_child_status_change (pid_t pid, int w)
   /* The process can have been deleted by Fdelete_process.  */
   for (tail = deleted_pid_list; CONSP (tail); tail = XCDR (tail))
     {
-      bool all_pids_are_fixnums
-        = (MOST_NEGATIVE_FIXNUM <= TYPE_MINIMUM (pid_t)
-           && TYPE_MAXIMUM (pid_t) <= MOST_POSITIVE_FIXNUM);
       Lisp_Object xpid = XCAR (tail);
-      if (all_pids_are_fixnums ? INTEGERP (xpid) : NUMBERP (xpid))
+      if ((INTEGERP (xpid) && pid == XINT (xpid))
+          || (FLOATP (xpid) && pid == XFLOAT_DATA (xpid)))
         {
-          pid_t deleted_pid;
-          if (INTEGERP (xpid))
-            deleted_pid = XINT (xpid);
-          else
-            deleted_pid = XFLOAT_DATA (xpid);
-          if (process_status_retrieved (deleted_pid, pid, &w))
-            {
-              XSETCAR (tail, Qnil);
-              if (record_at_most_one_child)
-                return;
-            }
+          XSETCAR (tail, Qnil);
+          return;
         }
     }
 
   /* Otherwise, if it is asynchronous, it is in Vprocess_alist.  */
+  p = 0;
   for (tail = Vprocess_alist; CONSP (tail); tail = XCDR (tail))
     {
-      Lisp_Object proc = XCDR (XCAR (tail));
-      struct Lisp_Process *p = XPROCESS (proc);
-      if (p->alive && process_status_retrieved (p->pid, pid, &w))
-        {
-          /* Change the status of the process that was found.  */
-          p->tick = ++process_tick;
-          p->raw_status = w;
-          p->raw_status_new = 1;
+      proc = XCDR (XCAR (tail));
+      p = XPROCESS (proc);
+      if (EQ (p->type, Qreal) && p->pid == pid)
+        break;
+      p = 0;
+    }
 
-          /* If process has terminated, stop waiting for its output.  */
-          if (WIFSIGNALED (w) || WIFEXITED (w))
-            {
-              int clear_desc_flag = 0;
-              p->alive = 0;
-              if (p->infd >= 0)
-                clear_desc_flag = 1;
+  /* Look for an asynchronous process whose pid hasn't been filled
+     in yet.  */
+  if (! p)
+    for (tail = Vprocess_alist; CONSP (tail); tail = XCDR (tail))
+      {
+        proc = XCDR (XCAR (tail));
+        p = XPROCESS (proc);
+        if (p->pid == -1)
+          break;
+        p = 0;
+      }
 
-              /* clear_desc_flag avoids a compiler bug in Microsoft C.  */
-              if (clear_desc_flag)
-                {
-                  FD_CLR (p->infd, &input_wait_mask);
-                  FD_CLR (p->infd, &non_keyboard_wait_mask);
-                }
-            }
+  /* Change the status of the process that was found.  */
+  if (p)
+    {
+      int clear_desc_flag = 0;
 
-          /* Tell wait_reading_process_output that it needs to wake up and
-             look around.  */
-          if (input_available_clear_time)
-            *input_available_clear_time = make_emacs_time (0, 0);
+      p->tick = ++process_tick;
+      p->raw_status = w;
+      p->raw_status_new = 1;
+
+      /* If process has terminated, stop waiting for its output.  */
+      if ((WIFSIGNALED (w) || WIFEXITED (w))
+          && p->infd >= 0)
+        clear_desc_flag = 1;
 
-          if (record_at_most_one_child)
-            return;
+      /* We use clear_desc_flag to avoid a compiler bug in Microsoft C.  */
+      if (clear_desc_flag)
+        {
+          FD_CLR (p->infd, &input_wait_mask);
+          FD_CLR (p->infd, &non_keyboard_wait_mask);
         }
-    }
 
-  if (0 <= pid)
+      /* Tell wait_reading_process_output that it needs to wake up and
+         look around.  */
+      if (input_available_clear_time)
+        *input_available_clear_time = make_emacs_time (0, 0);
+    }
+  /* There was no asynchronous process found for that pid: we have
+     a synchronous process.  */
+  else
     {
-      /* The caller successfully waited for a pid but no asynchronous
-         process was found for it, so this is a synchronous process.  */
-
       synch_process_alive = 0;
 
       /* Report the status of the synchronous process.  */
@@ -6405,10 +6392,38 @@ record_child_status_change (pid_t pid, int w)
 
 #ifdef SIGCHLD
 
+/* On some systems, the SIGCHLD handler must return right away.  If
+   any more processes want to signal us, we will get another signal.
+   Otherwise, loop around to use up all the processes that have
+   something to tell us.  */
+#if (defined WINDOWSNT \
+     || (defined USG && !defined GNU_LINUX \
+         && !(defined HPUX && defined WNOHANG)))
+enum { CAN_HANDLE_MULTIPLE_CHILDREN = 0 };
+#else
+enum { CAN_HANDLE_MULTIPLE_CHILDREN = 1 };
+#endif
+
 static void
 handle_child_signal (int sig)
 {
-  record_child_status_change (-1, 0);
+  do
+    {
+      pid_t pid;
+      int status;
+
+      do
+        pid = waitpid (-1, &status, WNOHANG | WUNTRACED);
+      while (pid < 0 && errno == EINTR);
+
+      /* PID == 0 means no processes found, PID == -1 means a real failure.
+         Either way, we have done all our job.  */
+      if (pid <= 0)
+        break;
+
+      record_child_status_change (pid, status);
+    }
+  while (CAN_HANDLE_MULTIPLE_CHILDREN);
 }
 
 static void
diff --git a/src/process.h b/src/process.h
index 74d1a124060..ce3d2e702cc 100644
--- a/src/process.h
+++ b/src/process.h
@@ -142,9 +142,6 @@ struct Lisp_Process
     /* Flag to set coding-system of the process buffer from the
        coding_system used to decode process output.  */
     unsigned int inherit_coding_system_flag : 1;
-    /* Whether the process is alive, i.e., can be waited for.  Running
-       processes can be waited for, but exited and fake processes cannot.  */
-    unsigned int alive : 1;
     /* Record the process status in the raw form in which it comes from `wait'.
        This is to avoid consing in a signal handler.  The `raw_status_new'
        flag indicates that `raw_status' contains a new status that still
diff --git a/src/sysdep.c b/src/sysdep.c
index bb81353847b..63eac5d9e09 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -289,6 +289,10 @@ wait_for_termination_1 (pid_t pid, int interruptible)
 {
   while (1)
     {
+#ifdef WINDOWSNT
+      wait (0);
+      break;
+#else /* not WINDOWSNT */
       int status;
       int wait_result = waitpid (pid, &status, 0);
       if (wait_result < 0)
@@ -302,8 +306,7 @@ wait_for_termination_1 (pid_t pid, int interruptible)
           break;
         }
 
-      /* Note: the MS-Windows emulation of waitpid calls QUIT
-         internally.  */
+#endif /* not WINDOWSNT */
       if (interruptible)
         QUIT;
     }
diff --git a/src/w32proc.c b/src/w32proc.c
index b4f2099f06a..e3c54fe5460 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -783,6 +783,7 @@ alarm (int seconds)
 /* Child process management list.  */
 int child_proc_count = 0;
 child_process child_procs[ MAX_CHILDREN ];
+child_process *dead_child = NULL;
 
 static DWORD WINAPI reader_thread (void *arg);
 
@@ -1035,6 +1036,9 @@ create_child (char *exe, char *cmdline, char *env, int is_gui_app,
   if (cp->pid < 0)
     cp->pid = -cp->pid;
 
+  /* pid must fit in a Lisp_Int */
+  cp->pid = cp->pid & INTMASK;
+
   *pPid = cp->pid;
 
   return TRUE;
@@ -1110,110 +1114,55 @@ reap_subprocess (child_process *cp)
     delete_child (cp);
 }
 
-/* Wait for a child process specified by PID, or for any of our
-   existing child processes (if PID is nonpositive) to die.  When it
-   does, close its handle.  Return the pid of the process that died
-   and fill in STATUS if non-NULL.  */
+/* Wait for any of our existing child processes to die
+   When it does, close its handle
+   Return the pid and fill in the status if non-NULL.  */
 
-pid_t
-waitpid (pid_t pid, int *status, int options)
+int
+sys_wait (int *status)
 {
   DWORD active, retval;
   int nh;
+  int pid;
   child_process *cp, *cps[MAX_CHILDREN];
   HANDLE wait_hnd[MAX_CHILDREN];
-  DWORD timeout_ms;
-  int dont_wait = (options & WNOHANG) != 0;
 
   nh = 0;
-  /* According to Posix:
-
-     PID = -1 means status is requested for any child process.
-
-     PID > 0 means status is requested for a single child process
-     whose pid is PID.
-
-     PID = 0 means status is requested for any child process whose
-     process group ID is equal to that of the calling process.  But
-     since Windows has only a limited support for process groups (only
-     for console processes and only for the purposes of passing
-     Ctrl-BREAK signal to them), and since we have no documented way
-     of determining whether a given process belongs to our group, we
-     treat 0 as -1.
-
-     PID < -1 means status is requested for any child process whose
-     process group ID is equal to the absolute value of PID.  Again,
-     since we don't support process groups, we treat that as -1.  */
-  if (pid > 0)
+  if (dead_child != NULL)
     {
-      int our_child = 0;
-
-      /* We are requested to wait for a specific child.  */
-      for (cp = child_procs + (child_proc_count-1); cp >= child_procs; cp--)
-        {
-          /* Some child_procs might be sockets; ignore them.  Also
-             ignore subprocesses whose output is not yet completely
-             read.  */
-          if (CHILD_ACTIVE (cp)
-              && cp->procinfo.hProcess
-              && cp->pid == pid)
-            {
-              our_child = 1;
-              break;
-            }
-        }
-      if (our_child)
-        {
-          if (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0)
-            {
-              wait_hnd[nh] = cp->procinfo.hProcess;
-              cps[nh] = cp;
-              nh++;
-            }
-          else if (dont_wait)
-            {
-              /* PID specifies our subprocess, but its status is not
-                 yet available.  */
-              return 0;
-            }
-        }
-      if (nh == 0)
-        {
-          /* No such child process, or nothing to wait for, so fail.  */
-          errno = ECHILD;
-          return -1;
-        }
+      /* We want to wait for a specific child */
+      wait_hnd[nh] = dead_child->procinfo.hProcess;
+      cps[nh] = dead_child;
+      if (!wait_hnd[nh]) emacs_abort ();
+      nh++;
+      active = 0;
+      goto get_result;
     }
   else
     {
       for (cp = child_procs + (child_proc_count-1); cp >= child_procs; cp--)
-        {
-          if (CHILD_ACTIVE (cp)
-              && cp->procinfo.hProcess
-              && (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0))
-            {
-              wait_hnd[nh] = cp->procinfo.hProcess;
-              cps[nh] = cp;
-              nh++;
-            }
-        }
-      if (nh == 0)
-        {
-          /* Nothing to wait on, so fail.  */
-          errno = ECHILD;
-          return -1;
-        }
+        /* some child_procs might be sockets; ignore them */
+        if (CHILD_ACTIVE (cp) && cp->procinfo.hProcess
+            && (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0))
+          {
+            wait_hnd[nh] = cp->procinfo.hProcess;
+            cps[nh] = cp;
+            nh++;
+          }
     }
 
-  if (dont_wait)
-    timeout_ms = 0;
-  else
-    timeout_ms = 1000;  /* check for quit about once a second. */
+  if (nh == 0)
+    {
+      /* Nothing to wait on, so fail */
+      errno = ECHILD;
+      return -1;
+    }
 
   do
     {
+      /* Check for quit about once a second. */
       QUIT;
-      active = WaitForMultipleObjects (nh, wait_hnd, FALSE, timeout_ms);
+      active = WaitForMultipleObjects (nh, wait_hnd, FALSE, 1000);
     } while (active == WAIT_TIMEOUT);
 
   if (active == WAIT_FAILED)
@@ -1243,10 +1192,8 @@ get_result:
     }
   if (retval == STILL_ACTIVE)
     {
-      /* Should never happen.  */
+      /* Should never happen */
       DebPrint (("Wait.WaitForMultipleObjects returned an active process\n"));
-      if (pid > 0 && dont_wait)
-        return 0;
       errno = EINVAL;
       return -1;
     }
@@ -1260,8 +1207,6 @@ get_result:
   else
     retval <<= 8;
 
-  if (pid > 0 && active != 0)
-    emacs_abort ();
   cp = cps[active];
   pid = cp->pid;
 #ifdef FULL_DEBUG
@@ -2050,7 +1995,9 @@ count_children:
               DebPrint (("select calling SIGCHLD handler for pid %d\n",
                          cp->pid));
 #endif
+              dead_child = cp;
               sig_handlers[SIGCHLD] (SIGCHLD);
+              dead_child = NULL;
             }
         }
       else if (fdindex[active] == -1)