【Linux】读写锁！！

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我是靠谱客的博主干净指甲油，这篇文章主要介绍【Linux】读写锁！！，现在分享给大家，希望可以做个参考。

读写锁的三二一模型

三：三种关系、读者与读者之间没有关系、写者和读者互斥且同步、写者与写者之间互斥
二：两种对象、读者和写者
一：一个交易场所
读写锁应用的场景：在多线程程序里面，线程对临界资源的访问比较多，而对临界资源的修改较少。

在读写者模型里面，由于写操作的次数比较少。那么在该模型里面的写操作的优先级必读操作的优先级高。加入读的优先级比写优先级高，那么就会出现读操作在一直读，写操作就会出现饥饿现象。

读写锁
类型：pthread_rwlock_t

初始化和销毁读写锁

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#include <pthread.h>
int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,
                        const pthread_rwlockattr_t *restrict attr);

读写锁的加锁和解锁

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int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);

实例：

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#include<stdio.h>
#include<pthread.h>
#include<unistd.h>

pthread_rwlock_t lock;
int count = 0;

void* route_read(void* arg){
    int id = (int)arg;
    int t = count;
    while(1){
        usleep(100000);
        pthread_rwlock_rdlock(&lock);
        printf("tid = %x  id = %d   t = %d  count = %dn",pthread_self(),id,t,count);
        pthread_rwlock_unlock(&lock);
        sleep(1);
    }
}

void* route_write(void* arg){
    int id = (int)arg;
    int t = count;
    while(1){
        usleep(100000);
        pthread_rwlock_wrlock(&lock);
        printf("tid = %x  id = %d   t = %d  ++count = %dn",pthread_self(),id,t,++count);
        pthread_rwlock_unlock(&lock);
        sleep(1);
    }
}

int main(){
    pthread_t id[8];
    int i = 0;
    pthread_rwlock_init(&lock,NULL);
    for(;i<3;i++){
        pthread_create(&id[i],NULL,route_write,(void*)i);
    }
    for(i=3;i<8;i++){
        pthread_create(&id[i],NULL,route_read,(void*)i);
    }
    for(i=0;i<8;i++)
        pthread_join(id[i],NULL);
    return 0;
}

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#include<stdio.h>
#include<pthread.h>
#include<unistd.h>

pthread_rwlock_t lock;
int count = 0;

void* route_read(void* arg){
    int id = (int)arg;
    int t = count;
    while(1){
        usleep(100000);
        pthread_rwlock_rdlock(&lock);
        printf("tid = %x  id = %d   t = %d  count = %dn",pthread_self(),id,t,count);
        pthread_rwlock_unlock(&lock);
        sleep(1);
    }
}

void* route_write(void* arg){
    int id = (int)arg;
    int t = count;
    while(1){
        usleep(100000);
        pthread_rwlock_wrlock(&lock);
        printf("tid = %x  id = %d   t = %d  ++count = %dn",pthread_self(),id,t,++count);
        pthread_rwlock_unlock(&lock);
        sleep(1);
    }
}

int main(){
    pthread_t id[8];
    int i = 0;
    pthread_rwlock_init(&lock,NULL);
    for(;i<3;i++){
        pthread_create(&id[i],NULL,route_write,(void*)i);
    }
    for(i=3;i<8;i++){
        pthread_create(&id[i],NULL,route_read,(void*)i);
    }
    for(i=0;i<8;i++)
        pthread_join(id[i],NULL);
    return 0;
}