环境配置

win10
pycharm64 5.0.3
python 3.6.7
tornado 5.1.1

代码块

    @staticmethod
    @gen.coroutine
    def send_req(req_obj, url="", params={}, body=None, method="GET", headers=None,
                 connect_timeout=None, request_timeout=None, max_clients=50):
        """
        异步HTTP接口调用封装
        """
        url = url_concat(url, params)
        try:
            request = HTTPRequest(url, method=method, body=body, headers=None,
                                  connect_timeout=connect_timeout, request_timeout=request_timeout, validate_cert=False)
        except:
            req_obj.app_exception("get HTTPRequest exception")
            return None

        try:
            response = yield AsyncHTTPClient(max_clients=max_clients).fetch(request)  # HTTPResponse
        except:
            # req_obj.app_exception("AsyncHTTPClient exception")
            logging.exception("AsyncHTTPClient exception")
            return None

在yield AsyncHTTPClient(max_clients=max_clients).fetch(request)中会实例化AsyncHTTPClient，执行fetch，返回一个future对象。后续也都会走runner = Runner(result, future, yielded)、future.add_done_callback(lambda _: runner)。

上游添加一个接口服务，加大接口的超时时间，打印接收到请求和请求完成的日志，tornado中起一个接口调用上述方法，这样就能够比较方便的定位tornado发出请求的代码位置。

最终定位的位置是

tornado/curl_httpclient.py
_handle_force_timeout
ret, num_handles = self._multi.socket_all() 此处进行的非阻塞请求