multiprocessing.Pool在Linux / Python2.7上的terminate（）之后生成新的子对象？

Question

我有一个可执行文件，需要使用不同的参数经常运行。为此，我按照此处给出的模式，使用多处理模块编写了一个小的Python（2.7）包装器。

我的代码如下所示：

try:
     logging.info("starting pool runs")
     pool.map(run_nlin, params)
     pool.close()
 except KeyboardInterrupt:
     logging.info("^C pressed")
     pool.terminate()
 except Exception, e:
     logging.info("exception caught: ", e)
     pool.terminate()
 finally:
     time.sleep(5)
     pool.join()
     logging.info("done")

我的工作者函数在这里：

class KeyboardInterruptError(Exception): pass

def run_nlin((path_config, path_log, path_nlin, update_method)):
    try:
        with open(path_log, "w") as log_:
            cmdline = [path_nlin, path_config]
            if update_method:
                cmdline += [update_method, ]
            sp.call(cmdline, stdout=log_, stderr=log_)
    except KeyboardInterrupt:
        time.sleep(5)
        raise KeyboardInterruptError()
    except:
        raise

path_config是二进制程序的配置文件的路径；例如，有运行该程序的日期。

当我启动包装器时，一切看起来都很好。但是，当我按时^C，包装脚本似乎numproc在终止之前从池中启动了其他进程。例如，当我在1-10天启动脚本时，在psaux输出中可以看到二进制程序的两个实例正在运行（通常在1天和3天）。现在，当我按时^C，包装脚本退出，第1天和第3天的二进制程序消失了，但是第5天和第7天又有新的二进制程序运行了。

因此对我来说，似乎在最终死亡之前Pool启动了另一个numproc进程。

有什么想法在这里发生什么，我能做些什么？

Answer 1

在此页面上，多处理模块的作者Jesse Noller显示正确的处理方式KeyboardInterrupt是让子流程返回-
不会引发异常。这允许主进程终止池。

但是，如下面的代码所示，except KeyboardInterrupt直到运行了由生成的所有任务 之后
，主流程才到达该块pool.map。这就是为什么（我相信）在按下run_nlin后会看到对辅助函数的额外调用Ctrl-C。

一种可能的解决方法是，如果multiprocessing.Event设置了a，则对所有工作程序功能进行测试。如果事件已发生，则请工人提早纾困，否则，请继续进行长时间的计算。

import logging
import multiprocessing as mp
import time

logger = mp.log_to_stderr(logging.WARNING)

def worker(x):
    try:
        if not terminating.is_set():
            logger.warn("Running worker({x!r})".format(x = x))
            time.sleep(3)
        else:
            logger.warn("got the message... we're terminating!")
    except KeyboardInterrupt:
        logger.warn("terminating is set")        
        terminating.set()
    return x

def initializer(terminating_):
    # This places terminating in the global namespace of the worker subprocesses.
    # This allows the worker function to access `terminating` even though it is
    # not passed as an argument to the function.
    global terminating
    terminating = terminating_

def main():
    terminating = mp.Event()    
    result = []
    pool = mp.Pool(initializer=initializer, initargs=(terminating, ))
    params = range(12)
    try:
         logger.warn("starting pool runs")
         result = pool.map(worker, params)
         pool.close()
    except KeyboardInterrupt:
        logger.warn("^C pressed")
        pool.terminate()
    finally:
        pool.join()
        logger.warn('done: {r}'.format(r = result))

if __name__ == '__main__':
    main()

运行脚本将产生：

% test.py
[WARNING/MainProcess] starting pool runs
[WARNING/PoolWorker-1] Running worker(0)
[WARNING/PoolWorker-2] Running worker(1)
[WARNING/PoolWorker-3] Running worker(2)
[WARNING/PoolWorker-4] Running worker(3)

在这里按Ctrl-C；每个工人都设置terminating事件。我们确实只需要设置它，但是尽管效率很低，但它仍然有效。

  C-c C-c[WARNING/PoolWorker-4] terminating is set
[WARNING/PoolWorker-2] terminating is set
[WARNING/PoolWorker-3] terminating is set
[WARNING/PoolWorker-1] terminating is set

现在，所有其他排队的任务pool.map都将运行：

[WARNING/PoolWorker-4] got the message... we're terminating!
[WARNING/PoolWorker-2] got the message... we're terminating!
[WARNING/PoolWorker-1] got the message... we're terminating!
[WARNING/PoolWorker-2] got the message... we're terminating!
[WARNING/PoolWorker-4] got the message... we're terminating!
[WARNING/PoolWorker-2] got the message... we're terminating!
[WARNING/PoolWorker-1] got the message... we're terminating!
[WARNING/PoolWorker-3] got the message... we're terminating!

最终，主要过程到达except KeyboardInterrupt块。

[WARNING/MainProcess] ^C pressed
[WARNING/MainProcess] done: []