Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : Sean Kelly
Date : Fri Aug 12 2005 02:05 pm

Joe Seigh wrote:
>
> Sean Kelly wrote:
> >
> > Exactly.  To make this point easier to understand, I suggest applying
> > it to a clustered system--each machine might implement synchronization
> > via message-passing.  In such an environment, it's obviously far more
> > efficient to only synchronize data altered within the critical section.
> >
> Locks don't just synchronize data altered within the critical section.
> They have release semantics for data altered before releasing the lock and
> acquire semantics for data accessed after acquiring the lock.  A lot of
> stuff would break otherwise.

True enough.  But does this matter so far as the POSIX spec is
concerned?  ie. I may know that this will work:

int i, j;

void* thread1(void*) {
    j = 1;
    // acquire mutex M
    i = 2;
    // release mutex M
}

void* thread2(void*) {
    // acquire mutex M
    if( i == 2 ) assert( j == 1 );
    // release mutex M
}

ie. the store for j must occur before the release of M in thread1.  But
the spec says nothing about this, correct?


Sean

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