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, 9 insertions, 0 deletions

diff --git a/Include/pythread.h b/Include/pythread.h
index 1cf83b7..bb9d864 100644
--- a/Include/pythread.h
+++ b/Include/pythread.h
@@ -36,6 +36,15 @@ PyAPI_FUNC(int) PyThread_acquire_lock(PyThread_type_lock, int);
 #define WAIT_LOCK       1
 #define NOWAIT_LOCK     0
 
+#ifndef Py_LIMITED_API
+#ifdef HAVE_FORK
+/* Private function to reinitialize a lock at fork in the child process.
+   Reset the lock to the unlocked state.
+   Return 0 on success, return -1 on error. */
+PyAPI_FUNC(int) _PyThread_at_fork_reinit(PyThread_type_lock *lock);
+#endif  /* HAVE_FORK */
+#endif  /* !Py_LIMITED_API */
+
 /* PY_TIMEOUT_T is the integral type used to specify timeouts when waiting
    on a lock (see PyThread_acquire_lock_timed() below).
    PY_TIMEOUT_MAX is the highest usable value (in microseconds) of that