[asterisk-dev] [Code Review]: Add a serializer interface to the threadpool

[David Lee]

> On Feb. 8, 2013, 4:23 p.m., Mark Michelson wrote:
> > /trunk/main/taskprocessor.c, lines 677-687
> > <https://reviewboard.asterisk.org/r/2323/diff/1/?file=33339#file33339line677>
> >
> >     This change is a bit troublesome. One of the reasons that tps_taskprocessor_pop() can return NULL is if the taskprocessor is shutting down. A common idiom in use is to loop calling ast_taskprocessor_execute() until it returns 0. Now if someone decides to shut down a taskprocessor that still has tasks in it, then the code that is looping over ast_taskprocessor_execute will not break out of its loop since ast_taskprocessor_execute will continually return non-zero.
> >     
> >     I think that if tps_taskprocessor_pop() returns NULL, we should unconditionally return 0 because either
> >     1) There were no tasks to pop off
> >     2) The taskprocessor has shut down and so we shouldn't be attempting to execute any more.

The problem there is the mentioned race condition. The listener never gets the 'was_empty' param set, but the processing thread stops processing.

The shutdown case is a problem, though. I'll create a unit test for it and take care of it.


> On Feb. 8, 2013, 4:23 p.m., Mark Michelson wrote:
> > /trunk/main/threadpool.c, lines 1116-1124
> > <https://reviewboard.asterisk.org/r/2323/diff/1/?file=33340#file33340line1116>
> >
> >     You should increase the refcount of pool when you set ser->pool. This way if someone were to shut down the threadpool before unreffing the serializer, they wouldn't run into trouble.
> >     
> >     Naturually this would mean decreasing the refcount in serializer_dtor()

fixed.


> On Feb. 8, 2013, 4:23 p.m., Mark Michelson wrote:
> > /trunk/tests/test_threadpool.c, line 1589
> > <https://reviewboard.asterisk.org/r/2323/diff/1/?file=33341#file33341line1589>
> >
> >     "highlanger?" Did you mean "highlander?"

yes.


- David


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On Feb. 8, 2013, 3:24 p.m., David Lee wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviewboard.asterisk.org/r/2323/
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> 
> (Updated Feb. 8, 2013, 3:24 p.m.)
> 
> 
> Review request for Asterisk Developers and Mark Michelson.
> 
> 
> Summary
> -------
> 
> This patch adds the ability to create a serializer from a thread pool. A
> serializer is a ast_taskprocessor with the same contract as a default
> taskprocessor (tasks execute serially) except instead of executing out
> of a dedicated thread, execution occurs in a thread from a
> ast_threadpool. Think of it as a lightweight thread.
> 
> While it guarantees that each task will complete before executing the
> next, there is no guarantee as to which thread from the pool individual
> tasks will execute. This normally only matters if your code relys on
> thread specific information, such as thread locals.
> 
> This patch also fixes a bug in how the 'was_empty' parameter is computed
> for the push callback.
> 
> 
> Diffs
> -----
> 
>   /trunk/include/asterisk/threadpool.h 381085 
>   /trunk/main/taskprocessor.c 381085 
>   /trunk/main/threadpool.c 381085 
>   /trunk/tests/test_threadpool.c 381085 
> 
> Diff: https://reviewboard.asterisk.org/r/2323/diff
> 
> 
> Testing
> -------
> 
> Unit testing.
> 
> 
> Thanks,
> 
> David
> 
>

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