一位用户在使用Python Queue时遇到了问题，在多线程中可以正常工作，但在多进程中却不行。他想要知道为什么会出现这种情况，以及如何解决。以下是问题的具体描述：
Threading implementation (works fine, makes sense to me):
from threading import Thread
from Queue import Queue
from time import sleep
"""threading functions"""
def producer_thread(n):
for x in range(10):
thread_q.put(n)
def consumer_thread():
while True:
item = thread_q.get()
print item
if __name__ == '__main__':
thread_q = Queue()
"""works fine"""
p_thread = Thread(target=producer_thread, args=(10,))
c_thread = Thread(target=consumer_thread)
c_thread.daemon=True
p_thread.start(); c_thread.start()
p_thread.join()
"""prevents c_thread daemon process from cancelling prematurely"""
sleep(.001)
Output:
10
10
10
10
10
10
10
10
10
10
Multiprocessing implementation (seems to be identical to threading but doesn't work at all):
from multiprocessing import Process, freeze_support
from Queue import Queue
"""multiprocessing functions"""
def producer_process(n):
for x in range(10):
process_q.put(n)
def consumer_process():
while True:
item = process_q.get()
print item
#
if __name__ == '__main__':
freeze_support()
process_q = Queue()
"""computer explodes"""
p_process = Process(target=producer_process, args=(10,))
c_process = Process(target=consumer_process)
c_process.daemon=True
p_process.start(); c_process.start()
p_process.join()
Output:
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Users\J\Anaconda\lib\multiprocessing\forking.py", line 381, in main
self = load(from_parent)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1378, in load
return Unpickler(file).load()
File "C:\Users\J\Anaconda\lib\pickle.py", line 858, in load
dispatch[key](self)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1090, in load_global
klass = self.find_class(module, name)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1126, in find_class
klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'get_successors'
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Users\J\Anaconda\lib\multiprocessing\forking.py", line 381, in main
self = load(from_parent)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1378, in load
return Unpickler(file).load()
File "C:\Users\J\Anaconda\lib\pickle.py", line 858, in load
dispatch[key](self)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1090, in load_global
klass = self.find_class(module, name)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1126, in find_class
klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'get_successors'
Process Process-33:
Traceback (most recent call last):
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 258, in _bootstrap
self.run()
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\J\Documents\Python Scripts\producer_consumer_test.py", line 18, in consumer
item = q.get()
NameError: global name 'q' is not defined
Process Process-32:
Traceback (most recent call last):
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 258, in _bootstrap
self.run()
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\J\Documents\Python Scripts\producer_consumer_test.py", line 14, in producer
q.put(n)
NameError: global name 'q' is not defined
Process Process-34:
Traceback (most recent call last):
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 258, in _bootstrap
self.run()
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\J\Documents\Python Scripts\producer_consumer_test.py", line 14, in producer
q.put(n)
NameError: global name 'q' is not defined
Process Process-35:
Traceback (most recent call last):
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 258, in _bootstrap
self.run()
File "C:\Users\J\Anaconda\lib\multiprocessing\process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "C:\Users\J\Documents\Python Scripts\producer_consumer_test.py", line 18, in consumer
item = q.get()
NameError: global name 'q' is not defined
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Users\J\Anaconda\lib\multiprocessing\forking.py", line 381, in main
self = load(from_parent)
File "C:\Users\J\Anaconda\lib\pickle.py", line 1378, in load
return Unpickler(file).load()
File "C:\Users\J\Anaconda\lib\pickle.py", line 85
