A.13 Using the flush Directive with a List

The following example uses the flush directive for point-to-point synchronization of specific objects between pairs of threads:

int   sync[NUMBER_OF_THREADS];
float work[NUMBER_OF_THREADS];
#pragma omp parallel private(iam,neighbor) shared(work,sync)
{
    iam = omp_get_thread_num();
    sync[iam] = 0;
    #pragma omp barrier

    // Do computation into my portion of work array 
    work[iam] = ...;

    //  Announce that I am done with my work
    // The first flush ensures that my work is
    // made visible before sync.
    // The second flush ensures that sync is made visible.
    #pragma omp flush(work)
    sync[iam] = 1;
    #pragma omp flush(sync)

    // Wait for neighbor
    neighbor = (iam>0 ? iam : omp_get_num_threads()) - 1;
    while (sync[neighbor]==0) 
    {
        #pragma omp flush(sync)
    }

    // Read neighbor's values of work array 
    ... = work[neighbor];
}