From 583bb07116505dcc73c0fc4aa3c1cf5074f3522d Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Miro=20Hron=C4=8Dok?= <miro@hroncok.cz>

Date: Fri, 2 Nov 2018 14:01:28 +0100

Subject: [PATCH] Revert "bpo-6721: Hold logging locks across fork() (GH-4071)

 (#9291)"

This reverts commit 3b699932e5ac3e76031bbb6d700fbea07492641d.

---

 Lib/logging/__init__.py  | 50 ------------------------------

 Lib/test/test_logging.py | 67 ----------------------------------------

 2 files changed, 117 deletions(-)

diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py

index 3ad2cc38f6..53780cd600 100644

--- a/Lib/logging/__init__.py

+++ b/Lib/logging/__init__.py

@@ -225,55 +225,6 @@ def _releaseLock():

     if _lock:

         _lock.release()

-

-# Prevent a held logging lock from blocking a child from logging.

-

-if not hasattr(os, 'register_at_fork'):  # Windows and friends.

-    def _register_at_fork_acquire_release(instance):

-        pass  # no-op when os.register_at_fork does not exist.

-else:  # The os.register_at_fork API exists

-    os.register_at_fork(before=_acquireLock,

-                        after_in_child=_releaseLock,

-                        after_in_parent=_releaseLock)

-

-    # A collection of instances with acquire and release methods (logging.Handler)

-    # to be called before and after fork.  The weakref avoids us keeping discarded

-    # Handler instances alive forever in case an odd program creates and destroys

-    # many over its lifetime.

-    _at_fork_acquire_release_weakset = weakref.WeakSet()

-

-

-    def _register_at_fork_acquire_release(instance):

-        # We put the instance itself in a single WeakSet as we MUST have only

-        # one atomic weak ref. used by both before and after atfork calls to

-        # guarantee matched pairs of acquire and release calls.

-        _at_fork_acquire_release_weakset.add(instance)

-

-

-    def _at_fork_weak_calls(method_name):

-        for instance in _at_fork_acquire_release_weakset:

-            method = getattr(instance, method_name)

-            try:

-                method()

-            except Exception as err:

-                # Similar to what PyErr_WriteUnraisable does.

-                print("Ignoring exception from logging atfork", instance,

-                      method_name, "method:", err, file=sys.stderr)

-

-

-    def _before_at_fork_weak_calls():

-        _at_fork_weak_calls('acquire')

-

-

-    def _after_at_fork_weak_calls():

-        _at_fork_weak_calls('release')

-

-

-    os.register_at_fork(before=_before_at_fork_weak_calls,

-                        after_in_child=_after_at_fork_weak_calls,

-                        after_in_parent=_after_at_fork_weak_calls)

-

-

 #---------------------------------------------------------------------------

 #   The logging record

 #---------------------------------------------------------------------------

@@ -844,7 +795,6 @@ class Handler(Filterer):

         Acquire a thread lock for serializing access to the underlying I/O.

         """

         self.lock = threading.RLock()

-        _register_at_fork_acquire_release(self)

     def acquire(self):

         """

diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py

index 1ea2967f5b..5d5eba7357 100644

--- a/Lib/test/test_logging.py

+++ b/Lib/test/test_logging.py

@@ -35,7 +35,6 @@ import os

 import queue

 import random

 import re

-import signal

 import socket

 import struct

 import sys

@@ -667,72 +666,6 @@ class HandlerTest(BaseTest):

                 if os.path.exists(fn):

                     os.unlink(fn)

-    # The implementation relies on os.register_at_fork existing, but we test

-    # based on os.fork existing because that is what users and this test use.

-    # This helps ensure that when fork exists (the important concept) that the

-    # register_at_fork mechanism is also present and used.

-    @unittest.skipIf(not hasattr(os, 'fork'), 'Test requires os.fork().')

-    def test_post_fork_child_no_deadlock(self):

-        """Ensure forked child logging locks are not held; bpo-6721."""

-        refed_h = logging.Handler()

-        refed_h.name = 'because we need at least one for this test'

-        self.assertGreater(len(logging._handlers), 0)

-

-        locks_held__ready_to_fork = threading.Event()

-        fork_happened__release_locks_and_end_thread = threading.Event()

-

-        def lock_holder_thread_fn():

-            logging._acquireLock()

-            try:

-                refed_h.acquire()

-                try:

-                    # Tell the main thread to do the fork.

-                    locks_held__ready_to_fork.set()

-

-                    # If the deadlock bug exists, the fork will happen

-                    # without dealing with the locks we hold, deadlocking

-                    # the child.

-

-                    # Wait for a successful fork or an unreasonable amount of

-                    # time before releasing our locks.  To avoid a timing based

-                    # test we'd need communication from os.fork() as to when it

-                    # has actually happened.  Given this is a regression test

-                    # for a fixed issue, potentially less reliably detecting

-                    # regression via timing is acceptable for simplicity.

-                    # The test will always take at least this long. :(

-                    fork_happened__release_locks_and_end_thread.wait(0.5)

-                finally:

-                    refed_h.release()

-            finally:

-                logging._releaseLock()

-

-        lock_holder_thread = threading.Thread(

-                target=lock_holder_thread_fn,

-                name='test_post_fork_child_no_deadlock lock holder')

-        lock_holder_thread.start()

-

-        locks_held__ready_to_fork.wait()

-        pid = os.fork()

-        if pid == 0:  # Child.

-            logging.error(r'Child process did not deadlock. \o/')

-            os._exit(0)

-        else:  # Parent.

-            fork_happened__release_locks_and_end_thread.set()

-            lock_holder_thread.join()

-            start_time = time.monotonic()

-            while True:

-                waited_pid, status = os.waitpid(pid, os.WNOHANG)

-                if waited_pid == pid:

-                    break  # child process exited.

-                if time.monotonic() - start_time > 7:

-                    break  # so long? implies child deadlock.

-                time.sleep(0.05)

-            if waited_pid != pid:

-                os.kill(pid, signal.SIGKILL)

-                waited_pid, status = os.waitpid(pid, 0)

-                self.fail("child process deadlocked.")

-            self.assertEqual(status, 0, msg="child process error")

-

 class BadStream(object):

     def write(self, data):

-- 

2.19.1