A.13 Using the flush Directive with a List

 

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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];  
}