1 files changed, 90 insertions, 37 deletions

diff --git a/src/w32proc.c b/src/w32proc.c
index 10dd23003b8..fd6a498290a 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -789,7 +789,6 @@ 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);
 
@@ -1042,9 +1041,6 @@ 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;
@@ -1120,55 +1116,110 @@ reap_subprocess (child_process *cp)
     delete_child (cp);
 }
 
-/* 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.  */
+/* 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.  */
 
-int
-sys_wait (int *status)
+pid_t
+waitpid (pid_t pid, int *status, int options)
 {
   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;
-  if (dead_child != NULL)
+  /* 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)
     {
-      /* 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;
+      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;
+	}
     }
   else
     {
       for (cp = child_procs + (child_proc_count-1); cp >= child_procs; cp--)
-	/* 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 (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;
+	}
     }
 
-  if (nh == 0)
-    {
-      /* Nothing to wait on, so fail */
-      errno = ECHILD;
-      return -1;
-    }
+  if (dont_wait)
+    timeout_ms = 0;
+  else
+    timeout_ms = 1000;	/* check for quit about once a second. */
 
   do
     {
-      /* Check for quit about once a second. */
       QUIT;
-      active = WaitForMultipleObjects (nh, wait_hnd, FALSE, 1000);
+      active = WaitForMultipleObjects (nh, wait_hnd, FALSE, timeout_ms);
     } while (active == WAIT_TIMEOUT);
 
   if (active == WAIT_FAILED)
@@ -1198,8 +1249,10 @@ 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;
     }
@@ -1213,6 +1266,8 @@ get_result:
   else
     retval <<= 8;
 
+  if (pid > 0 && active != 0)
+    emacs_abort ();
   cp = cps[active];
   pid = cp->pid;
 #ifdef FULL_DEBUG
@@ -2001,9 +2056,7 @@ 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)