Issue #14548: Make multiprocessing finalizers check pid before running

This protects from possibilty of gc running just after fork.

Lib/multiprocessing/util.py

@@ -9,6 +9,7 @@
 
 import sys
 import functools
+import os
 import itertools
 import weakref
 import atexit
@@ -161,6 +162,7 @@ class Finalize(object):
         self._args = args
         self._kwargs = kwargs or {}
         self._key = (exitpriority, next(_finalizer_counter))
+        self._pid = os.getpid()
 
         _finalizer_registry[self._key] = self
 
@@ -177,9 +179,13 @@ class Finalize(object):
         except KeyError:
             sub_debug('finalizer no longer registered')
         else:
-            sub_debug('finalizer calling %s with args %s and kwargs %s',
-                     self._callback, self._args, self._kwargs)
-            res = self._callback(*self._args, **self._kwargs)
+            if self._pid != os.getpid():
+                sub_debug('finalizer ignored because different process')
+                res = None
+            else:
+                sub_debug('finalizer calling %s with args %s and kwargs %s',
+                          self._callback, self._args, self._kwargs)
+                res = self._callback(*self._args, **self._kwargs)
             self._weakref = self._callback = self._args = \
                             self._kwargs = self._key = None
             return res

Misc/NEWS

@@ -44,6 +44,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #14548: Make multiprocessing finalizers check pid before
+  running to cope with possibility of gc running just after fork.
+
 - Issue #14863: Update the documentation of os.fdopen() to reflect the
   fact that it's only a thin wrapper around open() anymore.