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\
23 has built-in functions for atomic memory access.
24 #endif
25
26 static __inline__
sync_add_and_fetch(int * p,int i)27 int sync_add_and_fetch(int* p, int i)
28 {
29 return __sync_add_and_fetch(p, i);
30 }
31
32 static int s_x = 0;
33 /* g_dummy[] ensures that s_x and s_y are not in the same cache line. */
34 char g_dummy[512];
35 static int s_y = 0;
36
thread_func_1(void * arg)37 static 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
thread_func_2(void * arg)44 static 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
main(int argc,char ** argv)52 int 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