libgomp/testsuite/libgomp.c/appendix-a/a.18.1.c

   1 /* { dg-do run } */
   2
   3 #include <omp.h>
   4 #include <stdio.h>
   5
   6 extern void abort (void);
   7
   8 #define NUMBER_OF_THREADS 4
   9
  10 int synch[NUMBER_OF_THREADS];
  11 int work[NUMBER_OF_THREADS];
  12 int result[NUMBER_OF_THREADS];
  13 int
  14 fn1 (int i)
  15 {
  16   return i * 2;
  17 }
  18
  19 int
  20 fn2 (int a, int b)
  21 {
  22   return a + b;
  23 }
  24
  25 int
  26 main ()
  27 {
  28   int i, iam, neighbor;
  29   omp_set_num_threads (NUMBER_OF_THREADS);
  30 #pragma omp parallel private(iam,neighbor) shared(work,synch)
  31   {
  32     iam = omp_get_thread_num ();
  33     synch[iam] = 0;
  34 #pragma omp barrier
  35     /*Do computation into my portion of work array */
  36     work[iam] = fn1 (iam);
  37     /* Announce that I am done with my work. The first flush
  38      * ensures that my work is made visible before synch.
  39      * The second flush ensures that synch is made visible.
  40      */
  41 #pragma omp flush(work,synch)
  42     synch[iam] = 1;
  43 #pragma omp flush(synch)
  44     /* Wait for neighbor. The first flush ensures that synch is read
  45      * from memory, rather than from the temporary view of memory.
  46      * The second flush ensures that work is read from memory, and
  47      * is done so after the while loop exits.
  48      */
  49     neighbor = (iam > 0 ? iam : omp_get_num_threads ()) - 1;
  50     while (synch[neighbor] == 0)
  51       {
  52 #pragma omp flush(synch)
  53       }
  54 #pragma omp flush(work,synch)
  55     /* Read neighbor's values of work array */
  56     result[iam] = fn2 (work[neighbor], work[iam]);
  57   }
  58   /* output result here */
  59   for (i = 0; i < NUMBER_OF_THREADS; i++)
  60     {
  61       neighbor = (i > 0 ? i : NUMBER_OF_THREADS) - 1;
  62       if (result[i] != i * 2 + neighbor * 2)
  63         abort ();
  64     }
  65
  66   return 0;
  67 }