Tornado ThreadPoolExecutor 在产生结果时延迟请求

Question

系统规范 - MacOS 10.13.6 - Python 3.7.0 - Tornado 5.1.1

我想使用 ThreadPoolExecutor 在提供 RESTful 服务的 Tornado 实例中运行阻塞函数。

ThreadPool 会按预期工作并并行生成四个工作线程（请参阅下面的代码和控制台日志），只要我不试图产生由执行的函数返回的结果。

ThreadPoolExecutor 不产生结果

import time
import tornado.web
from tornado.concurrent import run_on_executor
from concurrent.futures import ThreadPoolExecutor
from tornado.ioloop import IOLoop

MAX_WORKERS = 4
i = 0

class Handler(tornado.web.RequestHandler):
    executor = ThreadPoolExecutor(max_workers=MAX_WORKERS)

    @run_on_executor
    def background_task(self, i):
        print("going sleep %s" % (i))
        time.sleep(10);
        print("waking up from sleep %s" % (i))
        return str(i)

    @tornado.gen.coroutine
    def get(self):
        global i
        i+=1
        self.background_task(i)


def make_app():
    return tornado.web.Application([
        (r"/", Handler),
    ])


if __name__ == "__main__":
    app = make_app()
    app.listen(8000, '0.0.0.0')
    IOLoop.current().start()        

控制台输出

going sleep 1
going sleep 2
going sleep 3
going sleep 4
waking up from sleep 1
going sleep 5
waking up from sleep 2
going sleep 6
waking up from sleep 3
going sleep 7
waking up from sleep 4
going sleep 8
waking up from sleep 5
going sleep 9
waking up from sleep 6
waking up from sleep 7
waking up from sleep 8
waking up from sleep 9

可以看出，有四个并行工作线程正在运行，并且一旦一个线程完成，就会执行一个排队的函数。

但是，当我尝试使用协程产生返回函数时，我遇到了一些问题。虽然它没有完全阻塞 IoLoop，但它会在没有明确模式的情况下被延迟。

更改代码：ThreadPoolExecutor 现在产生结果

MAX_WORKERS = 4
i = 0

class Handler(tornado.web.RequestHandler):
    executor = ThreadPoolExecutor(max_workers=MAX_WORKERS)

    @run_on_executor
    def background_task(self, i):
        print("%s: Going sleep %s" % (time.time(), i))
        time.sleep(10);
        print("%s: Waiking up from sleep %s" % (time.time(), i))
        return str(i)

    @tornado.gen.coroutine
    def get(self):
        global i
        i+=1
        result = yield self.background_task(i)
        self.write(result)

查看控制台输出，只有一个线程为第一个和第二个请求运行，在单个线程完成后执行排队任务（导致启动任务 2 延迟 10 秒，启动任务 3 延迟 10 秒）。然而，任务 3、4、5 和 6 是并行执行的，但在每次调用之间具有不同的延迟。

控制台输出

1548687401.331075: Going sleep 1
1548687411.333173: Waking up from sleep 1
1548687411.340162: Going sleep 2
1548687421.3419871: Waking up from sleep 2
1548687421.347039: Going sleep 3
1548687423.4030259: Going sleep 4
1548687423.884313: Going sleep 5
1548687424.6828501: Going sleep 6
1548687431.351986: Waking up from sleep 3
1548687431.3525162: Going sleep 7
1548687433.407232: Waking up from sleep 4
1548687433.407604: Going sleep 8
1548687433.8846452: Waking up from sleep 5
1548687433.885139: Going sleep 9
1548687434.685195: Waking up from sleep 6
1548687434.685662: Going sleep 10
1548687441.3577092: Waking up from sleep 7
1548687441.358009: Going sleep 11
1548687443.412503: Waking up from sleep 8
1548687443.888705: Waking up from sleep 9
1548687444.691127: Waking up from sleep 10
1548687451.359714: Waking up from sleep 11

谁能解释这种行为？你有什么解决办法吗？

Answer 1

根据CPU的配置和工作负载，进程分割任务。我们可以通过简单的启动 chrome 选项来测试并发性。