Python multiprocessing.Pool.map悄然死亡

我试图并行放置一个for循环来加快某些代码的速度。考虑一下：

from multiprocessing import Pool

results = []

def do_stuff(str):
    print str
    results.append(str)

p = Pool(4)
p.map(do_stuff, ['str1','str2','str3',...]) # many strings here ~ 2000
p.close()

print results

我显示了一些调试消息，do_stuff以跟踪程序在死亡之前能走多远。似乎每次都在不同的时间死去。例如，它将打印“ str297”，然后它将停止运行，我将看到所有CPU停止工作并且该程序就在那儿。应该发生一些错误，但是没有错误消息显示。有谁知道如何调试此问题？

更新

我尝试重新编写代码。map我没有使用此功能，而是尝试了以下apply_async功能：

        pool = Pool(5)
        results = pool.map(do_sym, underlyings[0::10])
        results = []
        for sym in underlyings[0::10]:
            r = pool.apply_async(do_sym, [sym])
            results.append(r)

        pool.close()
        pool.join()

        for result in results:
            print result.get(timeout=1000)

该map功能与该功能一样好，但是最终以相同的方式挂起。它永远不会到达for循环，在这里打印结果。

在进行了更多工作之后，尝试了像unutbu的答案中所建议的那样进行一些调试日志记录，我将在此处提供更多信息。这个问题很奇怪。好像游泳池只是挂在那里，无法关闭并继续执行该程序。我使用PyDev环境测试程序，但我想我会尝试仅在控制台中运行python。在控制台中，我得到了相同的行为，但是当我按Control + C杀死该程序时，我得到了一些输出，这些输出可以解释问题出在哪里：

> KeyboardInterrupt ^CProcess PoolWorker-47: Traceback (most recent call
> last):   File "/usr/lib/python2.7/multiprocessing/process.py", line
> 258, in _bootstrap Process PoolWorker-48: Traceback (most recent call
> last):   File "/usr/lib/python2.7/multiprocessing/process.py", line
> 258, in _bootstrap Process PoolWorker-45: Process PoolWorker-46:
> Process PoolWorker-44:
>     self.run()   File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
>     self._target(*self._args, **self._kwargs)   File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker
> Traceback (most recent call last): Traceback (most recent call last):
> Traceback (most recent call last):   File
> "/usr/lib/python2.7/multiprocessing/process.py", line 258, in
> _bootstrap   File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap   File
> "/usr/lib/python2.7/multiprocessing/process.py", line 258, in
> _bootstrap
>     task = get()   File "/usr/lib/python2.7/multiprocessing/queues.py", line 374, in get
>     self.run()   File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
>     racquire()
>     self._target(*self._args, **self._kwargs)   File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker
> KeyboardInterrupt
>     task = get()   File "/usr/lib/python2.7/multiprocessing/queues.py", line 374, in get
>     self.run()
>     self.run()   File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
>     self.run()   File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run   File
> "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
>     self._target(*self._args, **self._kwargs)   File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker
>     self._target(*self._args, **self._kwargs)
>     self._target(*self._args, **self._kwargs)   File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker
>     racquire()   File "/usr/lib/python2.7/multiprocessing/pool.py", line 102, in worker KeyboardInterrupt
>     task = get()   File "/usr/lib/python2.7/multiprocessing/queues.py", line 374, in get
>     task = get()
>     task = get()   File "/usr/lib/python2.7/multiprocessing/queues.py", line 376, in get  
> File "/usr/lib/python2.7/multiprocessing/queues.py", line 374, in get
>     racquire()
>     return recv()
>     racquire() KeyboardInterrupt KeyboardInterrupt KeyboardInterrupt

然后，实际上该程序永不消亡。我最终不得不关闭终端窗口以将其杀死。

更新2

我将问题缩小到池中正在运行的函数中，这是导致问题的MySQL数据库事务。我以前用过这个MySQLdb包裹。我将其切换pandas.read_sql为交易的一项功能，并且现在可以正常使用。