无法从多处理中运行一个过程

Question

我在测试我的浏览器应用程序时一直尝试运行一个进程。该过程是我进行 pytest 测试的固定装置之一，它应该在我开始测试时运行。但是，当我运行它时，它显示错误。我很困惑，因为这应该是一个简单的过程。这是我的代码：

@pytest.fixture(scope='class')
def chrome_driver(request):
    """ Selenium webdriver with options to support running in GitHub actions
    Note:
        For CI: `headless` and `disable-gpu` not commented out
        For running on your computer: `headless` and `disable-gpu` to be commented out
    """
    options = ChromeOptions()
    #options.add_argument("--headless")  # use for GitHub Actions CI
    #options.add_argument('--disable-gpu') # use for GitHub Actions CI
    options.add_argument("--window-size=1920,1080")
    chrome_driver = Chrome(options=options)
    request.cls.driver = chrome_driver
    yield
    chrome_driver.close()


@pytest.fixture(scope='class')
def run_app(app):
    """
    Fixture to run the Flask app for Selenium browser tests
    """
    multiprocessing.set_start_method("spawn")  # Needed in Python 3.8 and later
    #process = multiprocessing.Process(target=app.run, args=())
    #process.start()
    process = multiprocessing.Process(target=app.run, args=())
    process.start()
    process.join()
    yield process
    process.terminate()

上面是我测试的两个装置，它们将在我开始测试时同时运行。下面是错误：

test setup failed
app = <Flask 'flask_app'>

    @pytest.fixture(scope='class')
    def run_app(app):
        """
        Fixture to run the Flask app for Selenium browser tests
        """
        multiprocessing.set_start_method("spawn")  # Needed in Python 3.8 and later
        #process = multiprocessing.Process(target=app.run, args=())
        #process.start()
        process = multiprocessing.Process(target=app.run, args=())
>       process.start()

..\conftest.py:138: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
..\..\..\..\AppData\Local\Programs\Python\Python310\lib\multiprocessing\process.py:121: in start
    self._popen = self._Popen(self)
..\..\..\..\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py:224: in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
..\..\..\..\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py:327: in _Popen
    return Popen(process_obj)
..\..\..\..\AppData\Local\Programs\Python\Python310\lib\multiprocessing\popen_spawn_win32.py:93: in __init__
    reduction.dump(process_obj, to_child)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

obj = <Process name='Process-1' parent=26100 initial>
file = <_io.BufferedWriter name=11>, protocol = None

    def dump(obj, file, protocol=None):
        '''Replacement for pickle.dump() using ForkingPickler.'''
>       ForkingPickler(file, protocol).dump(obj)
E       AttributeError: Can't pickle local object 'Flask.__init__.<locals>.<lambda>'

Answer 1

如果我设置了多处理。set_start_method（“ fork”）并在IDE内部运行单个测试，那么我就可以得到类似的测试进行运行。一旦我在测试套件中运行它，我会出现“泡菜”错误。

Answer 2

正如亨利指出的那样，分叉将避免泡菜错误。在pytest会话中将会话范围内的固定装置设置为一次执行。

@pytest.fixture(scope='session')
def init_multiprocessing():
    multiprocessing.set_start_method("fork")


@pytest.fixture
def run_app(app, init_multiprocessing):
    process = multiprocessing.Process(target=app.run)
    process.start()
    yield process
    process.terminate()
    process.join()