I need to share an object and its methods between several processes in python. I am trying to use managers
(in module multiprocessing
) but it crashes. Here is a silly example of producer-consumer where the shared object between the two processes is just a list of numbers with four methods.
from multiprocessing import Process, Condition, Lock
from multiprocessing.managers import BaseManager
import time, os
lock = Lock()
waitC = Condition(lock)
waitP = Condition(lock)
class numeri(object):
def __init__(self):
self.nl = []
def getLen(self):
return len(self.nl)
def stampa(self):
print self.nl
def appendi(self, x):
self.nl.append(x)
def svuota(self):
for i in range(len(self.nl)):
del self.nl[0]
class numManager(BaseManager):
pass
numManager.register('numeri', numeri, exposed = ['getLen', 'appendi', 'svuota', 'stampa'])
def consume(waitC, waitP, listaNumeri):
lock.acquire()
if (listaNumeri.getLen() == 0):
waitC.wait()
listaNumeri.stampa()
listaNumeri.svuota()
waitP.notify()
lock.release()
def produce(waitC, waitP, listaNumeri):
lock.acquire()
if (listaNumeri.getLen() > 0):
waitP.wait()
for i in range(10):
listaNumeri.appendi(i)
waitC.notify()
lock.release()
def main():
mymanager = numManager()
mymanager.start()
listaNumeri = mymanager.numeri()
producer = Process(target = produce, args =(waitC, waitP, listaNumeri,))
producer.start()
time.sleep(2)
consumer = Process(target = consume, args =(waitC, waitP, listaNumeri,))
consumer.start()
main()
Anyway it always crashes like that, telling me this:
Process Process-3:
Traceback (most recent call last):
File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
self.run()
File "/usr/lib/python2.7/multiprocessing/process.py", line 114, in run
self._target(*self._args, **self._kwargs)
File "./trySemProc.py", line 61, in consume
if (listaNumeri.getLen() == 0):
File "<string>", line 2, in getLen
File "/usr/lib/python2.7/multiprocessing/managers.py", line 755, in _callmethod
self._connect()
File "/usr/lib/python2.7/multiprocessing/managers.py", line 742, in _connect
conn = self._Client(self._token.address, authkey=self._authkey)
File "/usr/lib/python2.7/multiprocessing/connection.py", line 169, in Client
c = SocketClient(address)
File "/usr/lib/python2.7/multiprocessing/connection.py", line 293, in SocketClient
s.connect(address)
File "/usr/lib/python2.7/socket.py", line 224, in meth
return getattr(self._sock,name)(*args)
error: [Errno 2] No such file or directory
So what's the matter? How should I use these managers
to share objects and their methods?
You must join your processes to prevent main process exiting before child processes continue their execution. So add joins to your code:
consumer.join()
producer.join()
after you called start()
methods of your processes.
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