读写锁的简单示例
/*使用读写锁实现四个线程读写一段程序的实例,共创建了四个新的线程,其中两个线程用来读取数据,另外两个线程用来写入数据。在任意时刻,如果有一个线程在写数据,将阻塞所有其他线程的任何操作。*/ #include <errno.h> #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <bits/pthreadtypes.h> pthread_rwlock_t rwlock;//读写锁对象 int a=0; void *thread_function_read_o(void *arg);//读线程1 void *thread_function_read_t(void *arg);//读线程2 void *thread_function_write_o(void *arg);//写线程1 void *thread_function_write_t(void *arg);//写线程2 int main(int argc,char *argv[]) { int res; pthread_t a_thread,b_thread,c_thread,d_thread; void *thread_result; res=pthread_rwlock_init(&rwlock,NULL);//初始化读写锁 if (res != 0) { perror("rwlock initialization failed"); exit(EXIT_FAILURE); } res = pthread_create(&a_thread, NULL, thread_function_read_o, NULL);//create new thread创建线程 if (res != 0) { perror("Thread creation failed"); exit(EXIT_FAILURE); } res = pthread_create(&b_thread, NULL, thread_function_read_t, NULL);//create new thread if (res != 0) { perror("Thread creation failed"); exit(EXIT_FAILURE); } res = pthread_create(&c_thread, NULL, thread_function_write_o, NULL);//create new thread if (res != 0) { perror("Thread creation failed"); exit(EXIT_FAILURE); } res = pthread_create(&d_thread, NULL, thread_function_write_t, NULL);//create new thread if (res != 0) { perror("Thread creation failed"); exit(EXIT_FAILURE); } res = pthread_join(a_thread, &thread_result);//等待a_thread线程结束 if (res != 0) { perror("Thread join failed"); exit(EXIT_FAILURE); } res = pthread_join(b_thread, &thread_result); if (res != 0) { perror("Thread join failed"); exit(EXIT_FAILURE); } res = pthread_join(c_thread, &thread_result); if (res != 0) { perror("Thread join failed"); exit(EXIT_FAILURE); } res = pthread_join(d_thread, &thread_result); if (res != 0) { perror("Thread join failed"); exit(EXIT_FAILURE); } res = pthread_rwlock_destroy(&rwlock);//销毁读写锁 if (res != 0) { perror("rwlock destory failed"); exit(EXIT_FAILURE); } } void *thread_function_read_o(void *arg) { pthread_rwlock_rdlock(&rwlock);//获取读取锁 printf("this is read thread1 get lock\n"); sleep(10); printf("read thread1:%d\n",a); pthread_rwlock_unlock(&rwlock); pthread_exit(0); } void *thread_function_read_t(void *arg) { pthread_rwlock_rdlock(&rwlock); printf("this is read thread2 get lock\n"); sleep(10); printf("read thread2:%d\n",a); pthread_rwlock_unlock(&rwlock); pthread_exit(0); } void *thread_function_write_o(void *arg) { pthread_rwlock_wrlock(&rwlock);//获取写入锁 printf("this is write thread1 get lock\n"); sleep(5); a++; printf("write thread1:%d\n",a); pthread_rwlock_unlock(&rwlock);//解锁 pthread_exit(0); } void *thread_function_write_t(void *arg) { pthread_rwlock_wrlock(&rwlock);//获取写入锁 printf("this is write thread2 get lock\n"); a+=2; sleep(5); printf("write thread2:%d\n",a); pthread_rwlock_unlock(&rwlock);//解锁 pthread_exit(0); }
程序中加的sleep仅仅是为了验证,同一时间只能有一个线程可以获取写入锁,但是可以有多个读者可以获取读取锁!