Avoid busy-waiting for child processes on Windows. (Bug#13086)

 src/w32proc.c (waitpid): Avoid busy-waiting when called with WNOHANG
 if the child process is still running.  Instead, exit the wait
 loop and return zero.

2 files changed, 16 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 2fefef1275b..2a138bfcf65 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2012-12-06  Eli Zaretskii  <eliz@gnu.org>
+
+        * w32proc.c (waitpid): Avoid busy-waiting when called with WNOHANG
+        if the child process is still running.  Instead, exit the wait
+        loop and return zero.  (Bug#13086)
+
 2012-12-06  Dmitry Antipov  <dmantipov@yandex.ru>
 
         * frame.h (x_char_width, x_char_height): Remove prototypes.
diff --git a/src/w32proc.c b/src/w32proc.c
index 87af8682390..0b36804b0e8 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -1220,13 +1220,22 @@ waitpid (pid_t pid, int *status, int options)
     {
       QUIT;
       active = WaitForMultipleObjects (nh, wait_hnd, FALSE, timeout_ms);
-    } while (active == WAIT_TIMEOUT);
+    } while (active == WAIT_TIMEOUT && !dont_wait);
 
   if (active == WAIT_FAILED)
     {
       errno = EBADF;
       return -1;
     }
+  else if (active == WAIT_TIMEOUT && dont_wait)
+    {
+      /* PID specifies our subprocess, but it didn't exit yet, so its
+         status is not yet available.  */
+#ifdef FULL_DEBUG
+      DebPrint (("Wait: PID %d not reap yet\n", cp->pid));
+#endif
+      return 0;
+    }
   else if (active >= WAIT_OBJECT_0
            && active < WAIT_OBJECT_0+MAXIMUM_WAIT_OBJECTS)
     {