On 12/04/2012 19:30, Al Niessner wrote:
Here is an update.
def subproc (i):
print ("From subprocess " + str(i))
print (b[:])
return
if __name__ == "__main__":
nproc = 3
print ("\nBuilding the array for the second computation.")
b = multiprocessing.Array (ctypes.c_double, nproc*nproc, lock=False)
print ("\nSending the task across to see what happens.")
pool = multiprocessing.Pool(nproc)
for i in range(nproc): pool.apply_async (subproc, kwds={'i':i})
pool.close()
pool.join()
pass
Does work. It is not what I need though. I need to be able to pass b as
an argument. The reason is that I create some of these in a loop and
they are not in a global space nor are they know prior to creating the
pool.
Doing this works:
processes = []
for i in range(nproc):
processes.append(multiprocessing.Process(target=subproc,
kwargs={'a':b, 'i':i}))
for p in processes:
p.start()
for p in processes:
p.join()
On Thu, 2012-04-12 at 11:15 -0700, Al Niessner wrote:
I am not subscribed to these lists but I do check them occasionally and
will check them more frequently looking for a response.
I am getting a pickling error that I do not understand. It seems the
shared arrays that I create cannot be pickled. Makes the
multiprocessing.Array fairly useless if it cannot be pickled. Hence, I
am guessing that I am doing something wrong and would like some help
spotting it.
This is basically a cut and paste from the examples in the
documentation:
import ctypes
import multiprocessing
def subproc (a, i):
print ("From subprocess " + str(i))
print (a[:])
return
if __name__ == "__main__":
nproc = 3
print ("\nBuilding the array for the second computation.")
b = multiprocessing.Array (ctypes.c_double, nproc*nproc, lock=False)
print ("\nSending the task across to see what happens.")
pool = multiprocessing.Pool(nproc)
for i in range(nproc): pool.apply_async (subproc, kwds={'a':b,
'i':i})
pool.close()
pool.join()
pass
Whether I run it on 2.6, 2.7, or 3.2 I get the same error.
Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
self.run()
File "/usr/lib/python2.6/threading.py", line 484, in run
self.__target(*self.__args, **self.__kwargs)
File "/usr/lib/python2.6/multiprocessing/pool.py", line 225, in
_handle_tasks
put(task)
PicklingError: Can't pickle<class
'multiprocessing.sharedctypes.c_double_Array_9'>: attribute lookup
multiprocessing.sharedctypes.c_double_Array_9 failed
Anyone want to take a stab as to why this error message is being
generated? Again I have tried python 2.6.7, 2.7.2+, and 3.2.2.
Thanks for any and all help in advance.
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