Method test_unpickle_module_race

Lib/test/pickletester.py:1698–1755

(self)

    @threading_helper.reap_threads
    @threading_helper.requires_working_threading()
    def test_unpickle_module_race(self):
        # https://bugs.python.org/issue34572
        locker_module = dedent("""
        import threading
        barrier = threading.Barrier(2)
        """)
        locking_import_module = dedent("""
        import locker
        locker.barrier.wait()
        class ToBeUnpickled(object):
            pass
        """)

        os.mkdir(TESTFN)
        self.addCleanup(shutil.rmtree, TESTFN)
        sys.path.insert(0, TESTFN)
        self.addCleanup(sys.path.remove, TESTFN)
        with open(os.path.join(TESTFN, "locker.py"), "wb") as f:
            f.write(locker_module.encode('utf-8'))
        with open(os.path.join(TESTFN, "locking_import.py"), "wb") as f:
            f.write(locking_import_module.encode('utf-8'))
        self.addCleanup(forget, "locker")
        self.addCleanup(forget, "locking_import")

        import locker

        pickle_bytes = (
            b'\x80\x03clocking_import\nToBeUnpickled\nq\x00)\x81q\x01.')

        # Then try to unpickle two of these simultaneously
        # One of them will cause the module import, and we want it to block
        # until the other one either:
        #   - fails (before the patch for this issue)
        #   - blocks on the import lock for the module, as it should
        results = []
        barrier = threading.Barrier(3)
        def t():
            # This ensures the threads have all started
            # presumably barrier release is faster than thread startup
            barrier.wait()
            results.append(pickle.loads(pickle_bytes))

        t1 = threading.Thread(target=t)
        t2 = threading.Thread(target=t)
        t1.start()
        t2.start()

        barrier.wait()
        # could have delay here
        locker.barrier.wait()

        t1.join()
        t2.join()

        from locking_import import ToBeUnpickled
        self.assertEqual(
            [type(x) for x in results],
            [ToBeUnpickled] * 2)