[cpp-threads] modes

[Alexander Terekhov]

On 5/7/05, Doug Lea <dl at cs.oswego.edu> wrote:
> 
> Alexander (and Peter?), how about you humor me and, for each mode you
> like not in minimal list, present a case that arguably meets the
> criteria ...
> 
> > only if there are compelling use cases for modes needed in
> > constructions that:
> >     1. arise in common or important situations,
> >     2. can't be expressed without special modes,
> >     3. will remain inefficient even when compilers start
> >        routinely optimizing wrt memory barriers etc in compliant code,
> >     4. will remain useful even as hardware vendors continue
> >        with their (very) recent trends to make most barriers etc cheaper
> >        (and thus less worthwhile to evade in corner cases).
> >
> 
> ... so we can discuss whether they pass some consensus threshold that
> we must establish.

<quote>

The minimal list seems to be along the lines of
   read-with-acquire
   write-with-release
   write-preserving-order
   CAS-with-acquire-release
   CAS-with-release

</quote>

Forget atomics for a moment.

Is this program

     #include <stdio.h>
     #include <pthread.h>

     pthread_rwlock_t rwlock;

     int var;

     void * thread(void *) {
       pthread_rwlock_rdlock(&rwlock);
       var = 0;
       //pthread_rwlock_unlock(&rwlock);
       return 0;
     }

     int main() {
       pthread_t tid;
       pthread_rwlock_init(&rwlock, 0);
       pthread_rwlock_wrlock(&rwlock);
       pthread_create(&tid, 0, thread, 0);
       var = 1;
       pthread_rwlock_unlock(&rwlock);
       pthread_join(tid, 0);
       printf("%d\n", var);
     }

data-race-free (under future C/C++/revised-POSIX memory model)?

Hopefully not.

regards,
alexander.