python - Python Concurrent.Futures ProcessPool Executor 错误输出

Question

我正在尝试使用 ProcessPoolExecutor() 来运行一些函数，但我无法理解如何从 with 中获取函数的返回。

 def threaded_upload(i):
    time.sleep(2)
    if i == 0:
        k = 10
    elif i == 2:
        k = i*i
    else:
        k = -99
    return [k]

 def controller():
    if __name__ == "__main__":
        futures = []
        with ProcessPoolExecutor() as pool:
            for paso in range(4):
                futuro_i = pool.submit(threaded_upload,paso)
                wth=[futuro_i.result()]
                futures.append(futuro_i)

            wait(futures, return_when=ALL_COMPLETED)

            merged_list = []
            for future in futures:
                for valor in future.result():
                    merged_list.append(valor)
            Lista_Final = merged_list
            wait(futures, return_when=ALL_COMPLETED)
        return Lista_Final

  print(controller())

代码的输出是：None [10, -99, 4, -99]

我不确定为什么？“等待”似乎也不会等到所有功能都执行完毕。

老实说，我已经阅读和阅读了几天，但是对 concurrent.futures 或多处理的描述比我目前的知识更先进。

任何澄清将不胜感激。提前致谢。

标签： pythonsubmitwaitconcurrent.futures

Answer 1

您首先提交作业，然后等待结果。您也可以返回一个整数而不是 alist然后跳过内部loop：

测试.py：

import random
import time

from concurrent.futures import ProcessPoolExecutor, wait


def worker(i):
    t = random.uniform(1, 5)

    print(f"START: {i} ({t:.3f}s)")

    time.sleep(t)

    if i == 0:
        k = 10
    elif i == 2:
        k = i * i
    else:
        k = -99

    print(f"END: {i}")

    return k


def main():
    futures = []

    with ProcessPoolExecutor() as pool:
        for i in range(4):
            future = pool.submit(worker, i)
            futures.append(future)

        results = []

        done, pending = wait(futures) # ALL_COMPLETED is the default value

        for future in done:
            results.append(future.result())

        print(results)


if __name__ == "__main__":
    main()

测试：

$ python test.py
START: 0 (1.608s)
START: 1 (1.718s)
START: 2 (1.545s)
START: 3 (1.588s)
END: 2
END: 3
END: 0
END: 1
[10, -99, 4, -99]