在使用multiprocessing模块同时下载我的宠物项目时，我遇到了一个涉及Queue对象生成的multiprocessing.Manager()个对象的奇怪行为。
根据我将Queue对象（通过Manager生成）放在另一个Queue对象（也是通过Manager生成）中的方式，我得到了不同的行为，我的理解，同样的事情。
这是一个最低限度的工作示例：
import multiprocessing
import Queue
def work(inbound_queue, keep_going):
while keep_going.value == 1:
try:
outbound_queue = inbound_queue.get(False) # this fails in case 3
#do some work
outbound_queue.put("work done!")
except Queue.Empty:
pass #this is busy wait of course, it's just an example
class Weird:
def __init__(self):
self.manager = multiprocessing.Manager()
self.queue = self.manager.Queue()
self.keep_going = multiprocessing.Value("i", 1)
self.worker = multiprocessing.Process(target = work, args = (self.queue, self.keep_going))
self.worker.start()
def stop(self): #close and join the second process
self.keep_going.value = 0
self.worker.join()
def queueFromOutside(self, q):
self.queue.put(q)
return q
def queueFromNewManager(self):
q = multiprocessing.Manager().Queue()
self.queue.put(q)
return q
def queueFromOwnManager(self):
q = self.manager.Queue()
self.queue.put(q)
return q
if __name__ == '__main__':
instance = Weird()
# CASE 1
queue = multiprocessing.Manager().Queue()
q1 = instance.queueFromOutside(queue) # Works fine
print "1: ", q1.get()
# CASE 2
q2 = instance.queueFromNewManager() # Works fine
print "2: ", q2.get()
# CASE 3
q3 = instance.queueFromOwnManager() # Error
print "3: ", q3.get()
instance.stop() #sadly never called :(
及其输出（python 2.7.10 x86，windows）。
主要输出：
1: work done!
2: work done!
3:
然后工作进程崩溃，让q3.get（）挂起。
工作流程的输出：
Process Process-2:
Traceback (most recent call last):
File "C:\Python27\lib\multiprocessing\process.py", line 258, in _bootstrap
self.run()
File "C:\Python27\lib\multiprocessing\process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "J:\Dropbox\Python\queues2.py", line 7, in work
outbound_queue = inbound_queue.get(False) # this fails in case 3
File "<string>", line 2, in get
File "C:\Python27\lib\multiprocessing\managers.py", line 774, in _callmethod
raise convert_to_error(kind, result)
RemoteError:
---------------------------------------------------------------------------
Unserializable message: ('#RETURN', <Queue.Queue instance at 0x025A22B0>)
---------------------------------------------------------------------------
所以问题是：为什么第三种情况导致RemoteError？
提供的示例与实际项目中的代码结构不相似，但我确实将队列发送到正在运行的进程，如果我使用方法＃1和＃2，它就可以正常工作。虽然使用方法＃3会很好，因为它可以省去每次获得Manager的麻烦，这可能会花费很长的时间（机器上约100毫秒我从右边开始工作）现在）。
这个问题出于好奇，因为我还在了解multiprocessing模块中所有很酷的东西。
更新，尝试澄清问题：，案例3（queueFromOwnManager）为什么self.manager.Queue()创建一个曾经放入self.queue的队列，不能使用self.queue.get()检索，而可以检索使用multiprocessing.Manager().Queue()创建的队列？执行3个案件的顺序无关紧要。理想情况下，instance.queue在3个示例中的3个方法调用之前和之后都将为空。
更新2：使得这个问题与我在代码中实际做的更相似
答案 0 :(得分：0)
更新了答案，我在main中添加了代码，用于从列表ls中填充和打印放置在队列self.queue中的项目。我还添加了一个语句，可用于从外部函数中的ls中检索self.queue中的项目。
import multiprocessing
import Queue
def work(inbound_queue, keep_going):
while keep_going.value == 1:
try:
pass
#outbound_queue = inbound_queue.get(False) # this fails in case 3 #<--- an error here, wherefrom does it get truthvalues?
#do some work
#outbound_queue.put("work done!")
except: #Queue.Empty: <--- self.queue.Empty(): when instantiated below
pass #this is busy wait of course, it's just an example
class Weird:
def __init__(self):
self.manager = multiprocessing.Manager()
self.queue = self.manager.Queue()
self.queue2 = multiprocessing.Manager().Queue()
self.keep_going = multiprocessing.Value("i", 1)
self.worker = multiprocessing.Process(target = work, args = (self.queue, self.keep_going))
self.worker.start()
def stop(self): #close and join the second process
self.keep_going.value = 0
#self.worker.join()
def queueFromOutside(self, q):
ls = [1,2,3,4,5]
# populate self.queue with elements from list ls
for i in ls:
self.queue.put(i)
return self.queue
def queueFromNewManager(self):
#q = multiprocessing.Manager().Queue() <---- note that you state that manager and not "queue"
# is the name of the queue in this step,
# therefor errormsg, at this step manager
# is empty and self.queue has been given ls
ls = [5,6,7,8]
# populate self.queue with elements from list ls
for i in ls:
self.queue.put(i)
return self.queue
def queueFromOwnManager(self):
q = self.manager.Queue()
ls = [5,6,7,8]
# populate self.queue with elements from list ls
for i in ls:
self.queue.put(i)
return self.queue
def wait_completion(self): #<---- function that waits until tasks are done, and joins all
# tasks as a last step, check docs how to add tasks and data to manager
"""Wait for completion of all the tasks in the queue"""
self.tasks.join()
if __name__ == '__main__':
instance = Weird()
# CASE 1
q1 = instance.queueFromOutside(instance.queue2) # Works fine
print "1: ", q1.get()
#this code gets data from instance.queue in external functions
if not instance.queue.empty():
item = instance.queue.get(True)
print item,"item"
# CASE 2
q2 = instance.queueFromNewManager() # Works fine
print "2: ", q2.get()
# CASE 3
q3 = instance.queueFromOwnManager() # Error
print "3: ", q3.get()
instance.stop() #sadly never called :(
# when all tasks done wait_completion(self) can be printed here to join all tasks