Python 的 ProcessPoolExecutor 以相反的顺序给出 print 和 return 语句的输出

Question

我在 Python 中练习使用多处理，所以我遇到了 concurrent.futures 模块。我尝试了运行以下代码：

import concurrent.futures
import time


def do_something(seconds):
    print(f'Sleeping {seconds} second(s)...')
    time.sleep(seconds)
    return f'Done Sleeping for {seconds} second(s)'

def main():

    with concurrent.futures.ProcessPoolExecutor() as executor:
        results = [executor.submit(do_something, 1.5) for _ in range(2)]

        for f in concurrent.futures.as_completed(results):
            print(f.result())


if __name__ == '__main__':
    start = time.perf_counter()
    main()
    finish = time.perf_counter()
    print(f'Finished in {round(finish-start, 2)} second(s)')

我应该期待类似下面的输出：

Sleeping 1.5 second(s)...
Sleeping 1.5 second(s)...
Done Sleeping for 1.5 second(s)
Done Sleeping for 1.5 second(s)
Finished in 1.5 second(s)

但是，我得到了：

Done Sleeping for 1.5 second(s)
Done Sleeping for 1.5 second(s)
Sleeping 1.5 second(s)...
Sleeping 1.5 second(s)...
Finished in 1.83 second(s)

return 语句出现在 print 语句之前是不是很奇怪？这是确切的片段： sublime_snip

Answer 1

这可能与标准输出缓冲有关。尝试在打印语句中传递 flush=True，例如：

print(f'Sleeping {seconds} second(s)...', flush=True)

您可以看到这是多进程打印的一个很常见的问题：Python multithreaded print statements delayed until all threads complete execution

Python 的 ProcessPoolExecutor 以相反的顺序给出 print 和 return 语句的输出

Python's ProcessPoolExecutor is giving output of print and return statement in reverse order

python

python-multiprocessing