Question

我的设置是python tornado服务器，它使用ThreadPoolExecutor异步处理任务。在某些情况下，任务可能会变成无限循环。使用with_timeout装饰器，我设法捕获超时异常并将错误结果返回给客户端。问题是该任务仍在后台运行。如何阻止任务在ThreadPoolExecutor中运行？或者是否可以取消Future？这是重现问题的代码。使用tornado 4和concurrent.futures库运行代码，然后转到http://localhost:8888/test

from tornado.concurrent import run_on_executor
from tornado.gen import with_timeout
from tornado.ioloop import IOLoop
import tornado.web
from tornado import gen
from concurrent.futures import ThreadPoolExecutor
import datetime
MAX_WAIT_SECONDS = 10

class MainHandler(tornado.web.RequestHandler):
    executor = ThreadPoolExecutor(2)

    @run_on_executor
    def test_func(self):
        ...
        #infinite loop might be here
        ...

    @tornado.gen.coroutine
    def get(self):
        future = self.test_func()
        try:
            result_search_struct = yield with_timeout(datetime.timedelta(seconds=MAX_WAIT_SECONDS), future )
            self.write({'status' : 0})
            self.finish()
        except Exception, e:
            #how to cancel the task here if it was timeout
            future.cancel() # <-- Does not work
            self.write({'status' : 100})
            self.finish()

application = tornado.web.Application([
    (r"/test", MainHandler),
])
application.listen(8888)
IOLoop.instance().start()

Answer 1

Future个实例在实际执行后无法取消，只有在它们处于暂挂状态时才能被取消。注意到in the docs：

取消（）

尝试取消通话。如果当前正在执行调用且无法取消，则该方法将返回False，   否则呼叫将被取消，方法将返回True。

因此，中止你在后台运行的方法的唯一方法是将逻辑插入到你的潜在无限循环中，以便在你告诉它时可以中止它。在您的示例中，您可以使用threading.Event：

class MainHandler(tornado.web.RequestHandler): executor = ThreadPoolExecutor(2) @run_on_executor def test_func(self, event): i = 0 while not event.is_set(): print i i = i + 1 @tornado.gen.coroutine def get(self): event = threading.Event() future = self.test_func(event) try: result_search_struct = yield with_timeout(datetime.timedelta(seconds=MAX_WAIT_SECONDS), future ) self.write({'status' : 0}) self.finish() except Exception, e: future.cancel() # Might not work, depending on how busy the Executor is event.set() self.write({'status' : 100}) self.finish() application = tornado.web.Application([ (r"/test", MainHandler), ])

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1 个答案: