Python threading/multiprocessing issue.

Brandon Harris brandon.harris at reelfx.com
Fri Jul 15 23:24:14 CEST 2011


I see. Well I was hoping to see the same result in the multiprocessing 
example as using the threading example. What you pointed out makes sense 
though, but what I don't understand is how modifying the queue in the 
example works fine in both. Possibly it was designed for that kind of use?

Brandon L. Harris


On 07/15/2011 03:55 PM, Lee Harr wrote:
>> I'm working on a tool that runs a number of process is separate thread.
>> I've, up to this point, been using threading.Thread, but from what I
>> read multiprocess will allow multiple processors to be used
>>    From the python docs on multiprocessing.
>> <Due to this, the multiprocessing module allows the programmer to fully
>>           leverage multiple processors on a given machine.>
>>
>> I have run into an issue when modifying the thread object from the run
>> method. Threading.thread allows me to change an attribute in the run
>> method and it hold while multiprocessing.Process loses it.
>
> I am not a multiprocessing expert, but I think the problem you
> are having is that Process is running your code in a separate
> process, so there is no way you could see those object changes
> in your main line code.
>
> In other words, Process is not an exact replacement for Thread.
> If you need to communicate between the different parts, you
> would want to use the abstractions provided by Queue or Pipe.
>
>
> Keep reading down the multiprocessing page in the docs until
> you get to "Exchanging objects between processes":
> http://docs.python.org/library/multiprocessing.html#exchanging-objects-between-processes
>
>
> "Sharing state between processes" seems like it will be especially
> relevant to what you are doing:
> http://docs.python.org/library/multiprocessing.html#sharing-state-between-processes
>
> Basically, it says "don't do that"  :o)
>
>
>> Here is an example illustrating the inconsistency that I've seen.
> One thing that would help here is a sample of what output
> you get from your code, and what you were hoping to get.
>
>   		 	   		




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