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Message from discussion The implementation of condition variables in pthreads-win32
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Alexander Terekhov  
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 More options May 21 2002, 7:08 am
Newsgroups: comp.os.ms-windows.programmer.win32, comp.programming.threads, microsoft.public.win32.programmer.kernel
From: Alexander Terekhov <terek...@web.de>
Date: Tue, 21 May 2002 12:54:28 +0200
Local: Tues, May 21 2002 6:54 am
Subject: Re: The implementation of condition variables in pthreads-win32
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Joerg Faschingbauer wrote:

> >>>>> "Alexander" == Alexander Terekhov <terek...@web.de> writes:

> Alexander> "Michael J. Saletnik" wrote:
> Alexander> [...]
> >> Having participated in an implementation of condition variables on
> >> Win32, it was very difficult to get right.

> Alexander> Could you please show us your impl (it is fairly simple
> Alexander> thing with thread-specific "blockers"/explicitly managed
> Alexander> queue)?

> I wonder what was the rationale to do it the complicated way.

"academic exercise" was the rationale! ;-)

Seriously, explicitly managed queue approach (like ZThreads's
one, presuming it's correctly implemented there ;-)) requires
making scheduling decisions -- wakeup order; think of priorities,
etc.

> I mean
> the current pthreads-win32 condvar implementation is difficult to
> grasp, and uses several OS objects for one condvar instance (where
> "normal" Unix condvars usually do not need any kernel resources).

It depends, I guess.

> The
> only reason I can think of is that you would be leaking the "blocker"
> object (an event, I assume) when you don't own thread creation and
> cleanup.

Well, it could be done even w/o owning thread creation and
cleanup -- just thread-specific events/semas (one would need
"correctly working" cleanup of thread-specific data, though;
that's somewhat a real challenge under brain-damaged win32-
native--without-pthreads-win32-I-mean ;-)).

> But when you are using pthreads-win32 you do own these.
> Or am I wrong?

Well, the pthreads-win32 CV-impl. could be simplified quite
considerably... As another "academic exercise" it tries to
fight (avoid generating of) spurious wakeups due to timeouts
and cancel; That's absolutely NOT required by the POSIX Threads
standard (*very wise decision*, given the presence of
"application"-induced "spurious" wakeups; and the simplicity/
robustness of while or do "waiting" loops), and given that extra
complexity and bookkeeping it takes to fight them (in the case
of pthreads-win32, I mean), is just counter productive,
I guess. ;-)

regards,
alexander.


 
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