OpenMP Application Programming Interface Examples

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1.11 The single Construct
The following example demonstrates the single construct. In the example, only one thread prints
each of the progress messages. All other threads will skip the single region and stop at the
barrier at the end of the single construct until all threads in the team have reached the barrier. If
other threads can proceed without waiting for the thread executing the single region, a nowait
clause can be specified, as is done in the third single construct in this example. The user must
not make any assumptions as to which thread will execute a single region.
Example single.1.c
C / C++
S-1 #include
S-2
S-3 void work1() {}
S-4 void work2() {}
S-5
S-6 void single_example()
S-7 {
S-8 #pragma omp parallel
S-9 {
S-10 #pragma omp single
S-11 printf("Beginning work1.\n");
S-12
S-13 work1();
S-14
S-15 #pragma omp single
S-16 printf("Finishing work1.\n");
S-17
S-18 #pragma omp single nowait
S-19 printf("Finished work1 and beginning work2.\n");
S-20
S-21 work2();
S-22 }
S-23 }
C / C++
CHAPTER 1. PARALLEL EXECUTION 27