Backport r60104 + r60111 from trunk.

gpshead · gpshead · commit 0e42f0e7991e · 2008-01-19T22:35:09.000Z
- Issue python#1336: fix a race condition in subprocess.Popen if the garbage collector kicked in at the wrong time that would cause the process to hang when the child wrote to stderr.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
@@ -346,6 +346,7 @@ class Popen(args, bufsize=0, executable=None,
 import os
 import types
 import traceback
+import gc
 
 if mswindows:
     import threading
@@ -899,7 +900,16 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
             errpipe_read, errpipe_write = os.pipe()
             self._set_cloexec_flag(errpipe_write)
 
-            self.pid = os.fork()
+            gc_was_enabled = gc.isenabled()
+            # Disable gc to avoid bug where gc -> file_dealloc ->
+            # write to stderr -> hang.  http://bugs.python.org/issue1336
+            gc.disable()
+            try:
+                self.pid = os.fork()
+            except:
+                if gc_was_enabled:
+                    gc.enable()
+                raise
             if self.pid == 0:
                 # Child
                 try:
@@ -958,6 +968,8 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                 os._exit(255)
 
             # Parent
+            if gc_was_enabled:
+                gc.enable()
             os.close(errpipe_write)
             if p2cread and p2cwrite:
                 os.close(p2cread)
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -26,6 +26,10 @@ Extension Modules
 Library
 -------
 
+- Issue #1336: fix a race condition in subprocess.Popen if the garbage
+  collector kicked in at the wrong time that would cause the process
+  to hang when the child wrote to stderr.
+
 - Bug #1728403: Fix a bug that CJKCodecs StreamReader hangs when it
   reads a file that ends with incomplete sequence and sizehint argument
   for .read() is specified.
