[SciPy-User] multiprocessing module

David Baddeley david_baddeley@yahoo.com...
Mon Nov 1 18:22:08 CDT 2010


If you want a simple solution which doesn't involve lots of syncronisation 
between the processes (depending on how often you write to disk this could prove 
to be quite a bottleneck), you might consider writing to a separate file from 
each process (perhaps using the pid as a unique identifier in the filename) and 
concatenating them at the end. 

cheers,
David


----- Original Message ----
From: Robert Kern <robert.kern@gmail.com>
To: SciPy Users List <scipy-user@scipy.org>
Sent: Tue, 2 November, 2010 11:50:09 AM
Subject: Re: [SciPy-User] multiprocessing module

On Mon, Nov 1, 2010 at 17:42, Ted To <forums@theo.to> wrote:
> On Mon, Nov 1, 2010 at 5:36 PM, Zachary Pincus <zachary.pincus@yale.edu> 
wrote:
>>> I'm trying to get multiprocess to do a bunch of independent
>>> calculations and save the results in a file and I'm probably going
>>> about it the wrong way.  I have a function defined "computeEq" that
>>> does the calculation and writes the result to a file (outfile) and I
>>> call it using:
>>>
>>> po = Pool()
>>> po.map_async(computeEq, product(rules,repeat=N))
>>> po.close()
>>> po.join()
>>> outfile.close()
>>>
>>> This seems to work for the most part but I seem to lose the last few
>>> calculations.  Indeed, one of my writes is truncated before the write
>>> is complete.
>>
>> Are you taking proper precautions so that multiple workers aren't
>> trying to write to the file at the same time?
>
> I'm a bit of a noob as far as multiprocessing goes so no, I'm not.
> How does one do that?

http://docs.python.org/library/multiprocessing#synchronization-between-processes

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco
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