[C++知识库]Linux C中的读写锁使用

读写锁的特点

读的时候不可以写  可以读 
写的时候不可以读
读写锁写的优先级高

代码环境

Ubuntu18.04+vscode C标准gnu11

/*
    读写锁的类型 pthread_rwlock_t
    int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock, const pthread_rwlockattr_t *restrict attr);
    int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
    int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
    读的时候不可以写  可以读 
    写的时候不可以读
    读写锁写的优先级高

    案例：8个线程操作同一个全局变量。
    3个线程不定时写这个全局变量，5个线程不定时的读这个全局变量
*/

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

// 创建一个共享数据
int num = 1;
// pthread_mutex_t mutex;
pthread_rwlock_t rwlock;

void * writeNum(void * arg) {

    while(num<50) {
        pthread_rwlock_wrlock(&rwlock);//写锁
        if(num<50){
            ++num;
            printf("++write, tid : %ld, num : %d\n", pthread_self(), num);
        }else{
            pthread_rwlock_unlock(&rwlock);
            break;
        }
        pthread_rwlock_unlock(&rwlock);
        usleep(100);
    }

    return NULL;
}

void * readNum(void * arg) {

    while(num<50) {
        pthread_rwlock_rdlock(&rwlock);//读锁
        if(num<50){
            printf("===read, tid : %ld, num : %d\n", pthread_self(), num);
        }else{
            pthread_rwlock_unlock(&rwlock);
            break;
        }
        pthread_rwlock_unlock(&rwlock);
        usleep(100);
    }

    return NULL;
}

int main() {

    //读写锁初始化
    pthread_rwlock_init(&rwlock, NULL);

    // 创建3个写线程，5个读线程
    pthread_t wtids[3], rtids[5];
    for(int i = 0; i < 3; i++) {
        pthread_create(&wtids[i],NULL,writeNum,NULL);
    }

    for(int i = 0; i < 5; i++) {
        pthread_create(&rtids[i], NULL, readNum, NULL);
    }

    // 设置线程分离
    for(int i = 0; i < 3; i++) {
       pthread_detach(wtids[i]);
    }

    for(int i = 0; i < 5; i++) {
         pthread_detach(rtids[i]);
    }

    //主线程结束,不会影响子线程
    pthread_exit(NULL);
    printf("main thread end！\n");//这一条不会执行

    //读写锁销毁
    pthread_rwlock_destroy(&rwlock);

    return 0;
}