简而言之
使用concurrent.futures并行编程时，我遇到了一个BrokenProcessPool异常。没有显示进一步的错误信息。我想找出错误的原因，并请教如何解决。
完整问题
我正在使用concurrent.futures来并行化一些代码。
with ProcessPoolExecutor() as pool:
mapObj = pool.map(myMethod, args)
最终我得到了（并且只得到了）以下异常：
concurrent.futures.process.BrokenProcessPool: A child process terminated abruptly, the process pool is not usable anymore
很遗憾，这个程序很复杂，错误只会在程序运行了30分钟后才出现。因此，我无法提供一个简单明了的最小示例。
为了找到问题的原因，我在并行运行的方法周围包了一个try-except块：
def myMethod(*args):
try:
...
except Exception as e:
print(e)
问题仍然存在，except块从未执行。我得出结论，异常并不来自我的代码。
接下来，我的下一步是编写一个自定义的ProcessPoolExecutor类，它是原始ProcessPoolExecutor的子类，并允许我替换其中一些方法为自定义方法。我复制并粘贴了方法_process_worker的原始代码，并添加了一些打印语句。
def _process_worker(call_queue, result_queue):
"""Evaluates calls from call_queue and places the results in result_queue.
...
"""
while True:
call_item = call_queue.get(block=True)
if call_item is None:
# Wake up queue management thread
result_queue.put(os.getpid())
return
try:
r = call_item.fn(*call_item.args, **call_item.kwargs)
except BaseException as e:
print("??? Exception ???") # newly added
print(e) # newly added
exc = _ExceptionWithTraceback(e, e.__traceback__)
result_queue.put(_ResultItem(call_item.work_id, exception=exc))
else:
result_queue.put(_ResultItem(call_item.work_id,
result=r))
同样地，except块永远不会被执行。这是可以预料的，因为我已经确保我的代码不会引发异常（如果一切正常，异常应该会传递到主进程）。
现在我缺乏想法如何找出错误。异常是在这里引发的:
def submit(self, fn, *args, **kwargs):
with self._shutdown_lock:
if self._broken:
raise BrokenProcessPool('A child process terminated '
'abruptly, the process pool is not usable anymore')
if self._shutdown_thread:
raise RuntimeError('cannot schedule new futures after shutdown')
f = _base.Future()
w = _WorkItem(f, fn, args, kwargs)
self._pending_work_items[self._queue_count] = w
self._work_ids.put(self._queue_count)
self._queue_count += 1
# Wake up queue management thread
self._result_queue.put(None)
self._start_queue_management_thread()
return f
这里将要中断进程池的运行：
def _queue_management_worker(executor_reference,
processes,
pending_work_items,
work_ids_queue,
call_queue,
result_queue):
"""Manages the communication between this process and the worker processes.
...
"""
executor = None
def shutting_down():
return _shutdown or executor is None or executor._shutdown_thread
def shutdown_worker():
...
reader = result_queue._reader
while True:
_add_call_item_to_queue(pending_work_items,
work_ids_queue,
call_queue)
sentinels = [p.sentinel for p in processes.values()]
assert sentinels
ready = wait([reader] + sentinels)
if reader in ready:
result_item = reader.recv()
else: #THIS BLOCK IS ENTERED WHEN THE ERROR OCCURS
# Mark the process pool broken so that submits fail right now.
executor = executor_reference()
if executor is not None:
executor._broken = True
executor._shutdown_thread = True
executor = None
# All futures in flight must be marked failed
for work_id, work_item in pending_work_items.items():
work_item.future.set_exception(
BrokenProcessPool(
"A process in the process pool was "
"terminated abruptly while the future was "
"running or pending."
))
# Delete references to object. See issue16284
del work_item
pending_work_items.clear()
# Terminate remaining workers forcibly: the queues or their
# locks may be in a dirty state and block forever.
for p in processes.values():
p.terminate()
shutdown_worker()
return
...
似乎有一个事实，即进程终止，但我不知道原因。到目前为止，我的想法正确吗？有哪些可能导致进程在没有消息的情况下终止的原因？（这可能吗？）我在哪里可以应用进一步的诊断？我应该问自己哪些问题才能更接近解决方案？
我正在64位Linux上使用Python 3.5。