如何等待ThreadPoolExecutor.map完成

问题描述

我有以下经过简化的代码:

import concurrent.futures

pool = concurrent.futures.ThreadPoolExecutor(8)

def _exec(x):
    return x + x

myfuturelist = pool.map(_exec,[x for x in range(5)])

# How do I wait for my futures to finish?

for result in myfuturelist:
    # Is this how it's done?
    print(result)

#... stuff that should happen only after myfuturelist is
#completely resolved.
# Documentation says pool.map is asynchronous

关于ThreadPoolExecutor.map的文档很弱。如果能帮上忙就太好了。

谢谢!


解决方案

Executor.map将并行运行作业,并等待Futures完成、收集结果并返回生成器。它已经为你做了等待。如果设置超时,它将一直等到超时,并在生成器中引发异常。

map(函数,*可迭代数,超时=无,块大小=1)

  • 立即收集可迭代对象,而不是延迟收集;
  • Func是异步执行的,可以同时调用Func。

要获取期货列表并手动执行等待,您可以使用:

myfuturelist = [pool.submit(_exec, x) for x in range(5)]

Executor.Submit将返回future对象,将来调用result将显式等待其完成:

myfutrelist[0].result() # wait the 1st future to finish and return the result

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