1/**
2 * This test program triggers a single race condition on variable s_y.
3 * Although another variable (s_x) is also modified by both threads, no race
4 * condition must be reported on this variable since it is only accessed via
5 * atomic instructions.
6 *
7 * Note: for the i386 and x86_64 memory models, thread 2 must print y = 1.
8 * On PPC however, both y = 0 and y = 1 are legal results. This is because
9 * the PPC memory model allows different CPU's to observe stores to variables
10 * in different cache lines in a different order.
11 */
12
13#define _GNU_SOURCE
14
15#include <pthread.h>
16#include <stdio.h>   /* fprintf() */
17#include <stdlib.h>  /* atoi() */
18#include "../../config.h"
19
20/* Atomic builtins are only supported by gcc 4.1.0 and later. */
21#ifndef HAVE_BUILTIN_ATOMIC
22#error Sorry, but this test program can only be compiled by a compiler that\
23has built-in functions for atomic memory access.
24#endif
25
26static __inline__
27int sync_add_and_fetch(int* p, int i)
28{
29  return __sync_add_and_fetch(p, i);
30}
31
32static int s_x = 0;
33/* g_dummy[] ensures that s_x and s_y are not in the same cache line. */
34char g_dummy[512];
35static int s_y = 0;
36
37static void* thread_func_1(void* arg)
38{
39  s_y = 1;
40  (void) sync_add_and_fetch(&s_x, 1);
41  return 0;
42}
43
44static void* thread_func_2(void* arg)
45{
46  while (sync_add_and_fetch(&s_x, 0) == 0)
47    ;
48  fprintf(stderr, "y = %d\n", s_y);
49  return 0;
50}
51
52int main(int argc, char** argv)
53{
54  int i;
55  const int n_threads = 2;
56  pthread_t tid[n_threads];
57
58  fprintf(stderr, "Start of test.\n");
59  pthread_create(&tid[0], 0, thread_func_1, 0);
60  pthread_create(&tid[1], 0, thread_func_2, 0);
61  for (i = 0; i < n_threads; i++)
62    pthread_join(tid[i], 0);
63  fprintf(stderr, "Test finished.\n");
64
65  return 0;
66}
67