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1 /** Cause a race inside code protected by a reader lock.
2  */
3 
4 
5 /* Needed for older glibc's (2.3 and older, at least) who don't
6    otherwise "know" about pthread_rwlock_anything or about
7    PTHREAD_MUTEX_RECURSIVE (amongst things). */
8 
9 #define _GNU_SOURCE 1
10 
11 #include <pthread.h>
12 #include <stdio.h>
13 #include <unistd.h>
14 
15 
16 
17 static pthread_rwlock_t s_rwlock;
18 static int s_racy;
19 
sleep_ms(const int ms)20 static void sleep_ms(const int ms)
21 {
22   struct timespec delay = { ms / 1000, (ms % 1000) * 1000 * 1000 };
23   nanosleep(&delay, 0);
24 }
25 
thread_func(void * arg)26 static void* thread_func(void* arg)
27 {
28   pthread_rwlock_rdlock(&s_rwlock);
29   s_racy++;
30   pthread_rwlock_unlock(&s_rwlock);
31   sleep_ms(100);
32   return 0;
33 }
34 
main(int argc,char ** argv)35 int main(int argc, char** argv)
36 {
37   pthread_t thread1;
38   pthread_t thread2;
39 
40 #if 0
41 
42   VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__DRD_TRACE_ADDR,
43                                   &s_racy, 0, 0, 0, 0);
44 #endif
45 
46   pthread_rwlock_init(&s_rwlock, 0);
47   pthread_create(&thread1, 0, thread_func, 0);
48   pthread_create(&thread2, 0, thread_func, 0);
49   pthread_join(thread1, 0);
50   pthread_join(thread2, 0);
51   pthread_rwlock_destroy(&s_rwlock);
52 
53   fprintf(stderr, "Result: %d\n", s_racy);
54 
55   return 0;
56 }
57