Subj : Re: Avoiding synchronization (pthreads)
To   : comp.programming.threads
From : Joe Seigh
Date : Wed Mar 02 2005 10:26 am

On Wed, 02 Mar 2005 15:39:44 +0100, Marcin 'Qrczak' Kowalczyk <qrczak@knm.org.pl> wrote:

> If a global variable of type int is read without holding a mutex, at
> the same time as other threads may write into it (holding the mutex),
> can anything worse than getting an out-of-date value happen in practice?
>
> The variable in question counts the number of threads. It is used
> to avoid locking in case there is only one thread. There may be
> background threads terminating asynchronously which decrement the
> variable. If the first paragraph is true, I should be safe, because
> an out-of-date value can only be larger than the true value, and
> in this case I will execute an equivalent but slower code (which
> takes the mutex, so the next time the variable will be up to date).
>

You'll need an acquire barrier after reading that there is only
one thread.  int has to be atomic of course.


-- 
Joe Seigh

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