[Python-Dev] [PEP 3148] futures - execute computations asynchronously

[Brian Quinlan]

On 10 Mar 2010, at 23:32, Nick Coghlan wrote:

> Brian Quinlan wrote:
>>> Getting rid of the process-global state like this simplifies testing
>>> (both testing of the executors themselves and of application code
>>> which uses them).  It also eliminates the unpleasant interpreter
>>> shutdown/module globals interactions that have plagued a number of
>>> stdlib systems that keep global state.
>>
>> I'm not sure what you mean, could you clarify?
>
> Assuming your question refers to the second sentence, Jean-Paul is
> referring to a trick of the CPython interpreter when it terminates. To
> maximise the chances of objects being deleted properly rather than  
> just
> dumped from memory when the process exits, module dictionaries are
> filled with None values before the interpreter shuts down.
>
> This can cause weirdness (usually intermittent name errors during
> shutdown) when __del__ methods directly or indirectly reference module
> globals.


Ah. I'm familiar with this problem. My approach was to install an exit  
handler that ensures that all pending futures are complete and all  
threads and processes exit before allowing the interpreter to exit.

Cheers,
Brian

> One of the easiest ways to avoid that is to put the state on a  
> singleton
> object, then give the affected classes a reference to that object.
>
> Cheers,
> Nick.
>
> P.S. This problem is actually the reason we don't have a context  
> manager
> for temporary directories yet. Something that should have been simple
> became a twisty journey down the rabbit hole:
> http://bugs.python.org/issue5178
>
> -- 
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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