Issue #12650: Fix a race condition where a subprocess.Popen could leak

resources (FD/zombie) when killed at the wrong time.

1 files changed, 6 insertions, 1 deletions

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 2d85b50..017f58d 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -429,12 +429,16 @@ try:
 except:
     MAXFD = 256
 
+# This lists holds Popen instances for which the underlying process had not
+# exited at the time its __del__ method got called: those processes are wait()ed
+# for synchronously from _cleanup() when a new Popen object is created, to avoid
+# zombie processes.
 _active = []
 
 def _cleanup():
     for inst in _active[:]:
         res = inst._internal_poll(_deadstate=sys.maxsize)
-        if res is not None and res >= 0:
+        if res is not None:
             try:
                 _active.remove(inst)
             except ValueError:
@@ -1191,6 +1195,7 @@ class Popen(object):
                                 errread, errwrite,
                                 errpipe_read, errpipe_write,
                                 restore_signals, start_new_session, preexec_fn)
+                        self._child_created = True
                     else:
                         # Pure Python implementation: It is not thread safe.
                         # This implementation may deadlock in the child if your