简而言之
当使用BrokenProcessPool对代码进行并行化时，会得到一个concurrent.futures异常。不显示进一步的错误。我想找出错误的原因，并询问如何做到这一点的想法。
完全问题
我正在使用concurrent.futures来并行化一些代码。
with ProcessPoolExecutor() as pool:
mapObj = pool.map(myMethod, args)
我最后得到（并且只得到）以下例外：
concurrent.futures.process.BrokenProcessPool: A child process terminated abruptly, the process pool is not usable anymore
不幸的是，程序很复杂，只有在程序运行30分钟后才会出现错误。因此，我不能提供一个很好的最小示例。
为了找出问题的原因，我将运行的方法与Try-Except块并行包装：
def myMethod(*args):
try:
...
except Exception as e:
print(e)
问题仍然存在，并且从未进入例外块。我的结论是，这个例外不是来自我的代码。
我的下一步是编写一个自定义的
ProcessPoolExecutor类，它是原始的ProcessPoolExecutor的子类，并允许我用自定义的方法替换一些方法。我复制粘贴了方法的原始代码，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，永远不会输入
_process_worker块。这是意料之中的，因为我已经确保了我的代码不会引发异常（如果一切正常，异常应该传递给主进程）。现在我不知道该如何找出错误。在此引发异常：
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
在此将进程池设置为断开：
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
...
进程终止是（或似乎是）一个事实，但我不知道为什么。到目前为止我的想法是正确的吗？导致进程在没有消息的情况下终止的可能原因是什么？（这是可能的吗？）在哪里可以应用进一步的诊断？为了更接近解决方案，我应该问自己哪些问题？
我正在64位Linux上使用python 3.5。
最佳答案
我想我能尽可能做到：
我更改了我的已更改模块中的_queue_management_worker方法，以便打印失败进程的退出代码：
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:
# BLOCK INSERTED FOR DIAGNOSIS ONLY ---------
vals = list(processes.values())
for s in ready:
j = sentinels.index(s)
print("is_alive()", vals[j].is_alive())
print("exitcode", vals[j].exitcode)
# -------------------------------------------
# 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
...
后来我查了出口代码的含义：
from multiprocessing.process import _exitcode_to_name
print(_exitcode_to_name[my_exit_code])
其中，
ProcessPoolExecutor是在插入到my_exit_code的块i中打印的退出代码。在我的例子中，代码是-11，这意味着我遇到了一个分段错误。找到这个问题的原因将是一项艰巨的任务，但超出了这个问题的范围。关于python - 在python concurrent.futures中查找BrokenProcessPool的原因，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/41454049/