multiprocessing and Locks

[gvv]

Hi All,

I am trying to understand multiprocessing, but I am getting a Runtime
error on the
code below. What am I missing or doing wrong?
Error is:
RuntimeError: Lock objects should only be shared between processes
through inheritance

I am using:
Python 2.6 (r26:66714, Nov 28 2008, 22:17:21)
[GCC 4.1.2 20071124 (Red Hat 4.1.2-42)] on linux2

Thanks in Advance,
George


import multiprocessing
import time

class Base(object):
def __init__(self, id, lock):
self.Id = id
lock.acquire()
self.Sleep()
lock.release()

def Run(self):
pass

def Sleep(self):
time.sleep(5)

class Derived(Base):
def __init__(self, id, lock):
Base.__init__(self, id, lock)

def Run(self):
print self.Id

def RunFunc(id, lock):
obj = Derived(id, lock)
obj.Run()

if __name__ == "__main__":
lock = multiprocessing.Lock()
Pool = multiprocessing.Pool(processes=5)
for i in xrange(100):
Pool.apply_async(func=RunFunc, args=(i,lock))
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Re: multiprocessing and Locks

[gvv]

On Apr 13, 3:30 am, Piet van Oostrum  wrote:
> >>>>> gvv  (G) wrote:
> >G> Hi All,
> >G> I am trying to understand multiprocessing, but I am getting a Runtime
> >G> error on the
> >G> code below. What am I missing or doing wrong?
> >G> Error is:
> >G> RuntimeError: Lock objects should only be shared between processes
> >G> through inheritance
>
> [code deleted]
>
> I guess you can't share locks (and probably other objects) between
> processes from a Pool. Maybe because there is no direct parent-child
> relation or so (there is a separate thread involved). There is nothing
> in the doc that explicitely forbids it AFAICT but it says that you have
> to be careful with sharing. But it could be a bug.
>
> You can do it with a manager, however, but this involves an additional
> process under the hood.
>
> if __name__ == "__main__":
>     manager = multiprocessing.Manager()
>     lock = manager.Lock()
>     pool = multiprocessing.Pool(processes=5)
>     for i in xrange(100):
>         pool.apply_async(func=RunFunc, args=(i,lock))
>     pool.close()
>     pool.join()
>
> --
> Piet van Oostrum 
> URL:http://pietvanoostrum.com[PGP 8DAE142BE17999C4]
> Private email: p...@vanoostrum.org

Hi Piet,

Thanks for your help. It worked.
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