简而言之
我将代码与BrokenProcessPool并行化时出现concurrent.futures异常。不会显示进一步的错误。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)
我最终得到（并且只有）以下异常：
concurrent.futures.process.BrokenProcessPool: A child process terminated abruptly, the process pool is not usable anymore
不幸的是，该程序很复杂，只有在程序运行30分钟后才会出现错误。因此，我无法提供一个很好的最小例子。
为了找到问题的原因，我用try-except-block包装了我运行的方法：
def myMethod(*args):
try:
...
except Exception as e:
print(e)
问题仍然存在，并且从未输入过块。我得出结论，异常并非来自我的代码。
我的下一步是编写一个自定义ProcessPoolExecutor类，它是原始ProcessPoolExecutor的子类，并允许我用cusomized方法替换某些方法。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，永远不会输入except块。这是可以预料到的，因为我已经确保我的代码不会引发异常（如果一切正常，则异常应该传递给主进程）。
现在我缺乏想法如何找到错误。这里引发了例外：
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
此处设置了进程池：
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
...
这是（或似乎是）一个过程终止的事实，但我不知道为什么。到目前为止我的想法是否正确？ 在没有消息的情况下使进程终止的可能原因是什么？ （这甚至可能吗？）我可以在哪里进一步诊断？我应该问自己哪些问题才能更接近解决方案？
我在64位Linux上使用python 3.5。
答案 0 :(得分：5)
我想我能够尽可能地获得：
我更改了更改后的_queue_management_worker模块中的ProcessPoolExecutor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
...
之后我查了退出代码的含义：
from multiprocessing.process import _exitcode_to_name
print(_exitcode_to_name[my_exit_code])
其中my_exit_code是我插入_queue_management_worker的块中打印的退出代码。在我的例子中，代码是-11，这意味着我遇到了分段错误。找出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。
答案 1 :(得分：1)
如果您使用的是macOS，则存在某些版本的macOS如何使用分支的已知问题，在某些情况下，Python认为这是不安全的。对我有用的解决方法是使用no_proxy环境变量。
编辑〜/ .bash_profile并包括以下内容（最好在此处指定域或子网列表，而不是*）
no_proxy='*'
刷新当前上下文
source ~/.bash_profile
我看到并解决过的本地版本是：Python 3.6.0 on macOS 10.14.1和10.13.x