读写者问题是一类比较特殊的问题。可以允许多个读者同时读，但不允许多个写者或者写者和读者同时操作。所以需要保证读者和写者之间的同步与互斥关系，以及多个写者之间的互斥关系。
读写锁是一种自旋锁：自旋锁是当一个线程没有申请资源成功，不会等待，而是一直在进行循环判断是否锁被释放。
1 #include2 #include 3 4 pthread_rwlock_t rwlock; 5 6 int buf; 7 void *reader(void *arg) 8 { 9 while(1) 10 { 11 pthread_rwlock_rdlock(&rwlock); 12 printf("reader%d is reading...:%d\n",(int)arg,buf); 13 pthread_rwlock_unlock(&rwlock); 14 sleep(1); 15 16 } 17 } 18 void *writer(void *arg) 19 { 20 int i = 0; 21 while(1) 22 { 23 pthread_rwlock_wrlock(&rwlock); 24 buf = i++; 25 printf("writer:%d\n",buf); 26 pthread_rwlock_unlock(&rwlock); 27 sleep(1); 28 } 29 } 30 31 int main() 32 { 33 pthread_t tid1,tid2,tid3,tid4; 34 pthread_create(&tid1,NULL,reader,(void*)1); 35 pthread_create(&tid3,NULL,reader,(void*)2); 36 pthread_create(&tid2,NULL,writer,NULL); 37 38 pthread_rwlock_init(&rwlock,NULL); 39 pthread_join(tid1,NULL); 40 pthread_join(tid3,NULL); 41 pthread_join(tid2,NULL); 42 pthread_rwlock_destroy(&rwlock); 43 return 0; 44 } 运行结果 [fbl@localhost rw_lock]$ ./rwlock writer:0reader2 is reading...:0reader1 is reading...:0writer:1reader2 is reading...:1reader1 is reading...:1writer:2reader2 is reading...:2reader1 is reading...:2writer:3reader2 is reading...:3reader1 is reading...:3writer:4reader2 is reading...:4reader1 is reading...:4writer:5reader2 is reading...:5reader1 is reading...:5writer:6reader2 is reading...:6reader1 is reading...:6