python - 我如何等待 ThreadPoolExecutor.map 完成

Question

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

有关 ThreadPoolExecutor.map 的文档薄弱。帮助会很棒。

谢谢!

Answer 1

对 ThreadPoolExecutor.map 的调用不会阻塞，直到它的所有任务都完成。使用 wait做这个。

from concurrent.futures import wait, ALL_COMPLETED
...

futures = [pool.submit(fn, args) for args in arg_list]
wait(futures, timeout=whatever, return_when=ALL_COMPLETED)  # ALL_COMPLETED is actually the default
do_other_stuff()

您还可以在 pool.map 返回的生成器上调用 list(results) 以强制执行评估(这是您在原始示例中所做的) .但是，如果您实际上没有使用任务返回的值，wait 是可行的方法。