cpython/Lib/test/test_atexit.py

import atexit
import os
import subprocess
import textwrap
import unittest
from test import support
from test.support import SuppressCrashReport, script_helper
from test.support import os_helper
from test.support import threading_helper

class GeneralTest(unittest.TestCase):
    def test_general(self):
        # Run _test_atexit.py in a subprocess since it calls atexit._clear()
        script = support.findfile("_test_atexit.py")
        script_helper.run_test_script(script)

class FunctionalTest(unittest.TestCase):
    def test_shutdown(self):
        # Actually test the shutdown mechanism in a subprocess
        code = textwrap.dedent("""
            import atexit

            def f(msg):
                print(msg)

            atexit.register(f, "one")
            atexit.register(f, "two")
        """)
        res = script_helper.assert_python_ok("-c", code)
        self.assertEqual(res.out.decode().splitlines(), ["two", "one"])
        self.assertFalse(res.err)

    def test_atexit_instances(self):
        # bpo-42639: It is safe to have more than one atexit instance.
        code = textwrap.dedent("""
            import sys
            import atexit as atexit1
            del sys.modules['atexit']
            import atexit as atexit2
            del sys.modules['atexit']

            assert atexit2 is not atexit1

            atexit1.register(print, "atexit1")
            atexit2.register(print, "atexit2")
        """)
        res = script_helper.assert_python_ok("-c", code)
        self.assertEqual(res.out.decode().splitlines(), ["atexit2", "atexit1"])
        self.assertFalse(res.err)

    @threading_helper.requires_working_threading()
    @support.requires_resource("cpu")
    @unittest.skipUnless(support.Py_GIL_DISABLED, "only meaningful without the GIL")
    def test_atexit_thread_safety(self):
        # GH-126907: atexit was not thread safe on the free-threaded build
        source = """
        from threading import Thread

        def dummy():
            pass


        def thready():
            for _ in range(100):
                atexit.register(dummy)
                atexit._clear()
                atexit.register(dummy)
                atexit.unregister(dummy)
                atexit._run_exitfuncs()


        threads = [Thread(target=thready) for _ in range(10)]
        for thread in threads:
            thread.start()

        for thread in threads:
            thread.join()
        """

        # atexit._clear() has some evil side effects, and we don't
        # want them to affect the rest of the tests.
        script_helper.assert_python_ok("-c", textwrap.dedent(source))

    @threading_helper.requires_working_threading()
    def test_thread_created_in_atexit(self):
        source =  """if True:
        import atexit
        import threading
        import time


        def run():
            print(24)
            time.sleep(1)
            print(42)

        @atexit.register
        def start_thread():
            threading.Thread(target=run).start()
        """
        return_code, stdout, stderr = script_helper.assert_python_ok("-c", source)
        self.assertEqual(return_code, 0)
        self.assertEqual(stdout, f"24{os.linesep}42{os.linesep}".encode("utf-8"))
        self.assertEqual(stderr, b"")

    @threading_helper.requires_working_threading()
    @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
    def test_thread_created_in_atexit_subinterpreter(self):
        try:
            from concurrent import interpreters
        except ImportError:
            self.skipTest("subinterpreters are not available")

        read, write = os.pipe()
        source = f"""if True:
        import atexit
        import threading
        import time
        import os

        def run():
            os.write({write}, b'spanish')
            time.sleep(1)
            os.write({write}, b'inquisition')

        @atexit.register
        def start_thread():
            threading.Thread(target=run).start()
        """
        interp = interpreters.create()
        try:
            interp.exec(source)

            # Close the interpreter to invoke atexit callbacks
            interp.close()
            self.assertEqual(os.read(read, 100), b"spanishinquisition")
        finally:
            os.close(read)
            os.close(write)

@support.cpython_only
class SubinterpreterTest(unittest.TestCase):

    def test_callbacks_leak(self):
        # This test shows a leak in refleak mode if atexit doesn't
        # take care to free callbacks in its per-subinterpreter module
        # state.
        n = atexit._ncallbacks()
        code = textwrap.dedent(r"""
            import atexit
            def f():
                pass
            atexit.register(f)
            del atexit
        """)
        ret = support.run_in_subinterp(code)
        self.assertEqual(ret, 0)
        self.assertEqual(atexit._ncallbacks(), n)

    def test_callbacks_leak_refcycle(self):
        # Similar to the above, but with a refcycle through the atexit
        # module.
        n = atexit._ncallbacks()
        code = textwrap.dedent(r"""
            import atexit
            def f():
                pass
            atexit.register(f)
            atexit.__atexit = atexit
        """)
        ret = support.run_in_subinterp(code)
        self.assertEqual(ret, 0)
        self.assertEqual(atexit._ncallbacks(), n)

    @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
    def test_callback_on_subinterpreter_teardown(self):
        # This tests if a callback is called on
        # subinterpreter teardown.
        expected = b"The test has passed!"
        r, w = os.pipe()

        code = textwrap.dedent(r"""
            import os
            import atexit
            def callback():
                os.write({:d}, b"The test has passed!")
            atexit.register(callback)
        """.format(w))
        ret = support.run_in_subinterp(code)
        os.close(w)
        self.assertEqual(os.read(r, len(expected)), expected)
        os.close(r)

    # Python built with Py_TRACE_REFS fail with a fatal error in
    # _PyRefchain_Trace() on memory allocation error.
    @unittest.skipIf(support.Py_TRACE_REFS, 'cannot test Py_TRACE_REFS build')
    def test_atexit_with_low_memory(self):
        # gh-140080: Test that setting low memory after registering an atexit
        # callback doesn't cause an infinite loop during finalization.
        code = textwrap.dedent("""
            import atexit
            import _testcapi

            def callback():
                print("hello")

            atexit.register(callback)
            # Simulate low memory condition
            _testcapi.set_nomemory(0)
        """)

        with os_helper.temp_dir() as temp_dir:
            script = script_helper.make_script(temp_dir, 'test_atexit_script', code)
            with SuppressCrashReport():
                with script_helper.spawn_python(script,
                                                stderr=subprocess.PIPE) as proc:
                    proc.wait()
                    stdout = proc.stdout.read()
                    stderr = proc.stderr.read()

        self.assertIn(proc.returncode, (0, 1))
        self.assertNotIn(b"hello", stdout)
        self.assertIn(b"MemoryError", stderr)


if __name__ == "__main__":
    unittest.main()