由于“您无法在与异步事件循环相同的线程中使用 AsyncToSync”错误，异步 Flask 端点无法同时工作

Question

这是重现该问题的最小蓝图：

@my_blueprint.route('/my_route', methods=['POST'])
async def my_route() -> Response:

    await asyncio.sleep(5)

    return format_json_response(
        {
            'success': True,
        },
    )

当一个接一个地拨打电话时，通话之间有一些延迟，它工作得非常好。但是，如果进行并发调用或只是进行串行调用太快，则会产生以下错误：

 Traceback (most recent call last):
    File "[myvenv]lib/python3.8/site-packages/gunicorn/workers/base_async.py", line 55, in handle
      self.handle_request(listener_name, req, client, addr)
    File "[myvenv]lib/python3.8/site-packages/gunicorn/workers/ggevent.py", line 127, in handle_request
      super().handle_request(listener_name, req, sock, addr)
    File "[myvenv]lib/python3.8/site-packages/gunicorn/workers/base_async.py", line 108, in handle_request
      respiter = self.wsgi(environ, resp.start_response)
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 2213, in __call__
      return self.wsgi_app(environ, start_response)
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 2193, in wsgi_app
      response = self.handle_exception(e)
    File "[myvenv]lib/python3.8/site-packages/flask_cors/extension.py", line 165, in wrapped_function
      return cors_after_request(app.make_response(f(*args, **kwargs)))
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 2190, in wsgi_app
      response = self.full_dispatch_request()
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 1486, in full_dispatch_request
      rv = self.handle_user_exception(e)
    File "[myvenv]lib/python3.8/site-packages/flask_cors/extension.py", line 165, in wrapped_function
      return cors_after_request(app.make_response(f(*args, **kwargs)))
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 1484, in full_dispatch_request
      rv = self.dispatch_request()
    File "[myvenv]lib/python3.8/site-packages/flask_protobuf/api.py", line 91, in dispatch_request
      rv = original_dispatch_request(self)
    File "[myvenv]lib/python3.8/site-packages/flask/app.py", line 1469, in dispatch_request
      return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
    File "[myvenv]lib/python3.8/site-packages/asgiref/sync.py", line 209, in __call__
      raise RuntimeError(
  RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop - just await the async function directly.

以下是一些额外的环境信息：

gevent==23.7.0
flask[async]==2.3.3
gunicorn[gevent]==20.1.0
gunicorn wsgi:app --workers=2 -k gevent

实际端点执行一些复杂的异步/等待并行处理，但其行为与这个最小示例完全相同。

我希望端点能够正常工作而不会出现任何错误消息。

Answer 1

我认为这个问题来自

async def my_route

。它将使用 AsyncToSync 类，因此它无法处理到 gevent 运行的主线程。

所以，将模式gunicorn更改为

gthread

来修复它。

gunicorn wsgi:app --workers=2 -k gthread