bpo-40089: Add _at_fork_reinit() method to locks (GH-19195)

Add a private _at_fork_reinit() method to _thread.Lock,
_thread.RLock, threading.RLock and threading.Condition classes:
reinitialize the lock after fork in the child process; reset the lock
to the unlocked state.

Rename also the private _reset_internal_locks() method of
threading.Event to _at_fork_reinit().

* Add _PyThread_at_fork_reinit() private function. It is excluded
  from the limited C API.
* threading.Thread._reset_internal_locks() now calls
  _at_fork_reinit() on self._tstate_lock rather than creating a new
  Python lock object.

1 files changed, 6 insertions, 0 deletions

diff --git a/Misc/NEWS.d/next/Library/2020-03-27-16-54-29.bpo-40089.VTq_8s.rst b/Misc/NEWS.d/next/Library/2020-03-27-16-54-29.bpo-40089.VTq_8s.rst
new file mode 100644
index 0000000..3948852
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-03-27-16-54-29.bpo-40089.VTq_8s.rst
@@ -0,0 +1,6 @@
+Add a private ``_at_fork_reinit()`` method to :class:`_thread.Lock`,
+:class:`_thread.RLock`, :class:`threading.RLock` and
+:class:`threading.Condition` classes: reinitialize the lock at fork in the
+child process, reset the lock to the unlocked state.
+Rename also the private ``_reset_internal_locks()`` method of
+:class:`threading.Event` to ``_at_fork_reinit()``.