Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : David Schwartz
Date : Fri Aug 12 2005 03:06 pm


"Sean Kelly" <sean@f4.ca> wrote in message 
news:1123877121.274302.229340@g44g2000cwa.googlegroups.com...

> 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?

    Everything would break if this was not the case. For example, a common 
pattern is to create an object, initialize it, acquire a lock, and add a 
pointer to that object so other threads can see it, then release the lock. 
This is why POSIX says that the mutex functions must synchronize memory.

    DS

.