Fixes issue #14396: Handle the odd rare case of waitpid returning 0

when not expected in subprocess.Popen.wait().

Lib/subprocess.py

@@ -1509,8 +1509,12 @@ class Popen(object):
                         raise TimeoutExpired(self.args, timeout)
                     delay = min(delay * 2, remaining, .05)
                     time.sleep(delay)
-            elif self.returncode is None:
+            else:
+                while self.returncode is None:
                     (pid, sts) = self._try_wait(0)
+                    # Check the pid and loop as waitpid has been known to return
+                    # 0 even without WNOHANG in odd situations.  issue14396.
+                    if pid == self.pid:
                         self._handle_exitstatus(sts)
             return self.returncode
 

Misc/NEWS

@@ -116,6 +116,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #14396: Handle the odd rare case of waitpid returning 0 when not
+  expected in subprocess.Popen.wait().
+
 - Issue #16411: Fix a bug where zlib.decompressobj().flush() might try to access
   previously-freed memory. Patch by Serhiy Storchaka.