Re: [boost] very poor thread performance

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-05-14 16:36:10

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On Wednesday 14 May 2008 16:24 pm, James Sutherland wrote:
> Phil,
> Thank you for your suggestions - I am hunting in the dark here...
>
> >>   for( int itask=0; itask<nTasks; ++itask ){
> >>     boost::thread_group threads;
> >>     for( int i=0; i<nThreads; ++i ){
> >>       threads.create_thread( MyStruct(itask++ + 100) );
> >>     }
> >>     threads.join_all();
> >>   }
> >
> > Did you really want the ++itask in the first for() ?  Isn't it being
> > incremented enough in the create_thread line?
>
> This was intentional.  This highly contrived example creates a fixed
> amount of work (nTasks) and divides them up among nThreads threads.
> As a thread takes a task, I increment itask.  Strange, I know...

No, if you also increment itask in the outer loop, you are doing fewer tasks 
when nThreads is smaller.  Although, what I said before about creating more 
threads than you think was wrong (I misunderstood your program).

- -- 
Frank
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