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 }
68