Python：等待所有`concurrent.futures.ThreadPoolExecutor`的期货
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Python: Wait on all of `concurrent.futures.ThreadPoolExecutor`'s futures
提问by Ram Rachum
I've given concurrent.futures.ThreadPoolExecutora bunch of tasks, and I want to wait until they're all completed before proceeding with the flow. How can I do that, without having to save all the futures and call waiton them? (I want an action on the executor.)
我给concurrent.futures.ThreadPoolExecutor了一堆任务，我想等到它们都完成后再继续流程。我怎样才能做到这一点，而不必保存所有期货并调用wait它们？（我想对执行者采取行动。）
采纳答案by Bakuriu
Just call Executor.shutdown:
只需致电Executor.shutdown：
shutdown(wait=True)Signal the executor that it should free any resources that it is using when the currently pending futures are done executing. Calls to
Executor.submit()andExecutor.map()made after shutdown will raiseRuntimeError.If wait is
Truethen this method will not return until all the pending futures are done executing and the resources associated with the executor have been freed.
shutdown(wait=True)当当前挂起的期货完成执行时，向执行器发出信号，它应该释放它正在使用的任何资源。关闭后调用
Executor.submit()和Executor.map()将引发RuntimeError.如果 wait 是，
True那么这个方法将不会返回，直到所有挂起的期货都执行完毕并且与执行程序关联的资源已被释放。
However if you keep track of your futures in a list then you can avoid shutting the executor down for future use using the futures.wait()function:
但是，如果您在列表中跟踪您的期货，那么您可以避免使用以下futures.wait()功能关闭执行程序以供将来使用：
concurrent.futures.wait(fs, timeout=None, return_when=ALL_COMPLETED)Wait for the
Futureinstances (possibly created by differentExecutorinstances) given byfsto complete. Returns a named 2-tuple of sets. The first set, named done, contains the futures that completed (finished or were cancelled) before the wait completed. The second set, named not_done, contains uncompleted futures.
concurrent.futures.wait(fs, timeout=None, return_when=ALL_COMPLETED)等待 给出的
Future实例（可能由不同的Executor实例创建 ）fs完成。返回一个命名的 2 元组集合。第一个名为 done 的集合包含在等待完成之前完成（完成或被取消）的期货。第二组名为 not_done，包含未完成的期货。
note that if you don't provide a timeoutit waits until all futures have completed.
请注意，如果您不提供 atimeout它会等到所有期货都完成。
You can also use futures.as_completed()instead, however you'd have to iterate over it.
您也可以futures.as_completed()改为使用，但是您必须对其进行迭代。
回答by laike9m
Bakuriu's answer is correct. Just to extend a little bit. As we all know a context manager has __enter__and __exit__method. Here is how class Executor(ThreadPoolExecutor's base class) is defined
巴库留的回答是正确的。只是为了扩展一点。众所周知，上下文管理器具有__enter__和__exit__方法。这是class Executor（ThreadPoolExecutor 的基类）是如何定义的
class Executor(object):
# other methods
def shutdown(self, wait=True):
"""Clean-up the resources associated with the Executor.
It is safe to call this method several times. Otherwise, no other
methods can be called after this one.
Args:
wait: If True then shutdown will not return until all running
futures have finished executing and the resources used by the
executor have been reclaimed.
"""
pass
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.shutdown(wait=True)
return False
And it is ThreadPoolExecutorthat actually defines the shutdownmethod
它ThreadPoolExecutor实际上定义了shutdown方法
class ThreadPoolExecutor(_base.Executor):
def shutdown(self, wait=True):
with self._shutdown_lock:
self._shutdown = True
self._work_queue.put(None)
if wait:
for t in self._threads:
t.join()
