A.9 Using single Directives

 

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The following example demonstrates the single directive (Section 2.4.3 on page 15). In the example, only one thread (usually the first thread that encounters the single directive) prints the progress message. The user must not make any assumptions as to which thread will execute the single section. All other threads will skip the single section and stop at the barrier at the end of the single construct. If other threads can proceed without waiting for the thread executing the single section, a nowait clause can be specified on the single directive.

#pragma omp parallel  
{  
    #pragma omp single  
        printf_s("Beginning work1.\n");  
    work1();  
    #pragma omp single  
        printf_s("Finishing work1.\n");  
    #pragma omp single nowait  
        printf_s("Finished work1 and beginning work2.\n");  
    work2();  
}