/* 定义读写锁 */pthread_rwlock_t rwlock;

/* 定义共享资源变量 */int g_nNum = 0;

/* 读操作 其他线程允许读操作 不允许写操作 */void *fun1(void *arg)  {      while(1)      {          pthread_rwlock_rdlock(&rwlock);          {            printf("read thread 1 == %d\n", g_nNum);        }              pthread_rwlock_unlock(&rwlock);

        sleep(1);    }}  

/* 读操作，其他线程允许读操作，不允许写操作 */void *fun2(void *arg){        while(1)    {        pthread_rwlock_rdlock(&rwlock);          {            printf("read thread 2 == %d\n", g_nNum);        }              pthread_rwlock_unlock(&rwlock);

        sleep(1);    }} 

/* 写操作，其它线程都不允许读或写操作 */void *fun3(void *arg){        while(1)    {        pthread_rwlock_wrlock(&rwlock);        {            g_nNum++;                    printf("write thread 1\n");        }        pthread_rwlock_unlock(&rwlock);        sleep(1);    }} /* 写操作，其它线程都不允许读或写操作 */ void *fun4(void *arg){        while(1)    {          pthread_rwlock_wrlock(&rwlock);          {            g_nNum++;              printf("write thread 2\n");          }        pthread_rwlock_unlock(&rwlock); 

        sleep(1);      }  }    int main(int arc, char *argv[])  {      pthread_t ThrId1, ThrId2, ThrId3, ThrId4;            pthread_rwlock_init(&rwlock, NULL);  // 初始化一个读写锁            /* 创建测试线程 */    pthread_create(&ThrId1, NULL, fun1, NULL);      pthread_create(&ThrId2, NULL, fun2, NULL);      pthread_create(&ThrId3, NULL, fun3, NULL);      pthread_create(&ThrId4, NULL, fun4, NULL);            /* 等待线程结束，回收其资源 */    pthread_join(ThrId1, NULL);      pthread_join(ThrId2, NULL);      pthread_join(ThrId3, NULL);      pthread_join(ThrId4, NULL);            pthread_rwlock_destroy(&rwlock);      // 销毁读写锁            return 0;  }