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读写锁适合于对数据结构的读次数比写次数多得多的情况.因为,读模式锁定时可以共享,以写 模式锁住时意味着独占,所以读写锁又叫共享-独占锁.
初始化和销毁:
#include <pthread.h>
int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock, const
pthread_rwlockattr_t *restrict attr);
int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);成功则返回0,出错则返回错误编号. 同互斥量以上,在释放读写锁占用的内存之前,需要先通过 pthread_rwlock_destroy对读写锁进行清理工作, 释放由init分配的资源.
读和写:
#include <pthread.h>
int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);成功则返回0,出错则返回错误编号.这3个函数分别实现获取读锁,获取写锁和释放锁的操作.获 取锁的两个函数是阻塞操作,同样,非阻塞的函数为:
#include <pthread.h>
int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);成功则返回0,出错则返回错误编号.非阻塞的获取锁操作,如果可以获取则返回0,否则返回 错误的EBUSY.
代码:
/********* 说明: ********* 读写锁适合于对数据结构的读次数比写次数多得多的情况.因为, ******** 读模式锁定时可以共享,以写 模式锁住时意味着独占,所以读写锁又叫共享-独占锁. ******** 要让读者与写者之间、以及写者与写者之问要互斥地访同数据集； *********/ #include <pthread.h> #include <signal.h> #include <stdio.h> //#include "apue.h" #define R 5 // reader NO. #define W 5 // reader and writer NO. pthread_rwlock_t lock; //it‘s mean writer can writing int readCount = 0; void* reader(void *arg) { int n = W; int id = *(int*)arg; while (n--) { sleep( rand() % 3 ); pthread_rwlock_rdlock(&lock); printf("reader %d is reading\n", id); sleep( rand() % 3 ); pthread_rwlock_unlock(&lock); printf("reader %d is leaving\n", id); } printf("----reader %d has done----\n", id); } void* writer(void *arg) { int n = W; while (n--) { sleep( rand() % 3 ); pthread_rwlock_wrlock(&lock); printf("\twriter is writing\n"); sleep( rand() % 3 ); pthread_rwlock_unlock(&lock); printf("\twriter is leaving\n"); } printf("----writer has done----\n"); } int main(int argc, const char *argv[]) { int err; pthread_t tid[R], writerTid; int i; err = pthread_create(&writerTid, NULL, writer, (void *)NULL); if (err != 0) { printf("can‘t create process for writer\n"); } pthread_rwlock_init(&lock, NULL); for (i = 0; i < R; i++) { err = pthread_create(&tid[i], NULL, reader, &i); if (err != 0) { printf("can‘t create process for reader"); } } while(1); pthread_rwlock_destroy(&lock); return 0; }
读写锁是一种写优先的互斥锁．
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原文地址：http://www.cnblogs.com/biglucky/p/4631582.html
