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A.5 Using the critical Directive

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The following example includes several critical directives (Section 2.6.2 on page 18). The example illustrates a queuing model in which a task is dequeued and worked on. To guard against multiple threads dequeuing the same task, the dequeuing operation must be in a critical section. Because the two queues in this example are independent, they are protected by critical directives with different names, xaxis and yaxis.

#pragma omp parallel shared(x, y) private(x_next, y_next)  
{  
    #pragma omp critical ( xaxis )  
        x_next = dequeue(x);  
    work(x_next);  
    #pragma omp critical ( yaxis )  
        y_next = dequeue(y);  
    work(y_next);  
}