Function _after_fork

Lib/threading.py:1596–1638

Cleanup threading module state that should not exist after a fork.

()

def _after_fork():
    """
    Cleanup threading module state that should not exist after a fork.
    """
    # Reset _active_limbo_lock, in case we forked while the lock was held
    # by another (non-forked) thread.  http://bugs.python.org/issue874900
    global _active_limbo_lock, _main_thread
    _active_limbo_lock = RLock()

    # fork() only copied the current thread; clear references to others.
    new_active = {}

    try:
        current = _active[get_ident()]
    except KeyError:
        # fork() was called in a thread which was not spawned
        # by threading.Thread. For example, a thread spawned
        # by thread.start_new_thread().
        current = _MainThread()

    _main_thread = current

    with _active_limbo_lock:
        # Dangling thread instances must still have their locks reset,
        # because someone may join() them.
        threads = set(_enumerate())
        threads.update(_dangling)
        for thread in threads:
            # Any lock/condition variable may be currently locked or in an
            # invalid state, so we reinitialize them.
            if thread is current:
                # This is the one and only active thread.
                ident = get_ident()
                thread._after_fork(new_ident=ident)
                new_active[ident] = thread
            else:
                # All the others are already stopped.
                thread._after_fork()

        _limbo.clear()
        _active.clear()
        _active.update(new_active)
        assert len(_active) == 1


if hasattr(_os, "register_at_fork"):