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https://github.com/Zenithsiz/ftmemsim-valgrind.git
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73 lines
1.6 KiB
C
73 lines
1.6 KiB
C
/** Race condition around use of atomic variable.
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* Note: for the i386 and x86_64 memory models, thread 2 must print y = 1.
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* On PPC however, both y = 0 and y = 1 are legal results. This is because
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* the PPC memory model allows different CPU's to observe stores to variables
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* in different cache lines in a different order.
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*/
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#define _GNU_SOURCE
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#include "config.h"
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#include <pthread.h>
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#include <stdio.h> /* fprintf() */
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#include <stdlib.h> /* atoi() */
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/** Only gcc 4.1.0 and later have atomic builtins. */
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#ifndef HAVE_BUILTIN_ATOMIC
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static __inline__
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int __sync_add_and_fetch(int* p, int i)
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{
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if (i == 0)
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return *p;
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return (*p += i);
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}
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#endif
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static int s_x = 0;
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/* s_dummy[] ensures that s_x and s_y are not in the same cache line. */
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static char s_dummy[512];
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static int s_y = 0;
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static void* thread_func_1(void* arg)
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{
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s_y = 1;
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(void) __sync_add_and_fetch(&s_x, 1);
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return 0;
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}
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static void* thread_func_2(void* arg)
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{
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while (__sync_add_and_fetch(&s_x, 0) == 0)
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;
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fprintf(stderr, "y = %d\n", s_y);
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return 0;
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}
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int main(int argc, char** argv)
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{
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#ifdef HAVE_BUILTIN_ATOMIC
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int i;
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const int n_threads = 2;
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pthread_t tid[n_threads];
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fprintf(stderr, "Start of test.\n");
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pthread_create(&tid[0], 0, thread_func_1, 0);
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pthread_create(&tid[1], 0, thread_func_2, 0);
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for (i = 0; i < n_threads; i++)
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pthread_join(tid[i], 0);
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fprintf(stderr, "Test finished.\n");
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#else
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fprintf(stderr,
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"Sorry, but your compiler does not have built-in support for atomic"
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" operations.\n");
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#endif
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/* Suppress the compiler warning about s_dummy not being used. */
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s_dummy[0]++;
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return 0;
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}
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