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Re: Goodbye to threads

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From:
Dan Sugalski
Date:
August 20, 2002 01:57
Subject:
Re: Goodbye to threads
Message ID:
a05111b15b987b24a06fe@[63.120.19.221]
At 9:31 AM +0200 8/20/02, Elizabeth Mattijsen wrote:
>At 11:00 PM 8/19/02 +0100, Dave Mitchell wrote:
>>On Mon, Aug 19, 2002 at 10:16:11PM +0200, Elizabeth Mattijsen wrote:
>>  > Please note that all of these runs all did the _same_ amount of work,
>>  > just with a different number of worker threads.  And as the job itself
>>  > is minimal, we're basically measuring overhead here.  The benchmark is
>>  > not measuring thread startup or thread shutdown, just what happens
>>  > inside the threads themselves.
>>But your code is not using cond_wait()/cond_signal() correctly, so you just
>>have lots of clients actively fighting each other for the lock.
>
>Well, I would be interested in knowing how you _should_ use 
>cond_wait()/cond_signal() then.  I don't see how you can get it 
>together so that the clients are _not_ fighting for the lock(). 
>Because that is the basic problem that I see Perl threads now have.

There's nothing wrong with the clients fighting for the lock. That's 
what locks are for, after all--to allow you to protect critical 
sections of code. Conditions are only supposed to be used when you 
need explicit coordination between threads. They *aren't* supposed to 
be used as a general critical section  protection. (That's what locks 
are for) Perl's thread model, even with the changes, isn't much 
different than the POSIX thread model.

It's hard to say for sure, having only seen the code you've posted 
with this thread, but are you sure that maybe you're not missing 
something somewhere? That benchmark was pretty meaningless, and the 
explanation attached to it seemed to miss the point rather badly. 
(That might be a language issue, or a convoluted benchmark problem)
-- 
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
dan@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk

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