weakref.py 文件源码

def _exitfunc(cls):
        # At shutdown invoke finalizers for which atexit is true.
        # This is called once all other non-daemonic threads have been
        # joined.
        reenable_gc = False
        try:
            if cls._registry:
                import gc
                if gc.isenabled():
                    reenable_gc = True
                    gc.disable()
                pending = None
                while True:
                    if pending is None or finalize._dirty:
                        pending = cls._select_for_exit()
                        finalize._dirty = False
                    if not pending:
                        break
                    f = pending.pop()
                    try:
                        # gc is disabled, so (assuming no daemonic
                        # threads) the following is the only line in
                        # this function which might trigger creation
                        # of a new finalizer
                        f()
                    except Exception:
                        sys.excepthook(*sys.exc_info())
                    assert f not in cls._registry
        finally:
            # prevent any more finalizers from executing during shutdown
            finalize._shutdown = True
            if reenable_gc:
                gc.enable()