系统编程:互斥锁,条件变量

互斥锁

使用过程:
1,声明锁: pthread_mutex_t lock;
2,初始化锁:pthread_mutex_init(&lock,NULL);
3,在线程的方法函数中上锁和解锁:(成对出现)
pthread_mutex_lock(&lock);
pthread_mutex_unlock(&lock);
4,销毁锁:pthread_mutex_destroy(&lock);

代码示例:

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

pthread_mutex_t lock;//在全局区声明互斥锁

void *tick(void *arg)
{
    static int num =10;
    while(num>0){
        pthread_mutex_lock(&lock);
        if(num<=0)
        {
            pthread_mutex_unlock(&lock);
            break;
        }
        num--;
        sleep(1);
        printf("线程%ld销售了一张票,还剩%d张\n",pthread_self(),num);
        pthread_mutex_unlock(&lock);
    }
}

int main(int argc,char const *argv[])
{
    pthread_mutex_init(&lock,NULL);//初始化互斥锁
    pthread_t p1,p2,p3,p4; //定义四个线程;共享此进程的数据

    pthread_create(&p1,NULL,tick,NULL);
    pthread_create(&p2,NULL,tick,NULL);
    pthread_create(&p3,NULL,tick,NULL);
    pthread_create(&p4,NULL,tick,NULL);//创建四个线程

    pthread_join(p1,NULL);
    pthread_join(p2,NULL);
    pthread_join(p3,NULL);
    pthread_join(p4,NULL);//等待四个线程结束
    
    pthread_mutex_destroy(&lock);//销毁互斥锁
    return 0;
}
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互斥锁+条件变量

条件变量:使用过程:
1,声明条件变量 pthread_cond_t cond;
2,初始化条件变量 pthread_cond_init(&cond,NULL);
3,在一对互斥锁中间:pthread_cond_wait(&cond,&lock);//会打开互斥锁,并且阻塞程序,–直到另一个信号函数pthread_cond_broadcast(&cond);被执行时解除阻塞.或者pthread_cond_signal(&cond)函数;
4,释放条件变量pthread_cond_destroy(&cond);

代码示例:生产者-消费者模型

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <string.h>
#include <time.h>
#include <stdlib.h>

pthread_mutex_t lock;//声明互斥锁
pthread_cond_t cond; //声明条件变量

int num = 0; //声明记录库存数量的变量

void *produce(void *argv)
{
    while(1){
        pthread_mutex_lock(&lock);
        while(num >= 10)
        {
            printf("库存已满,线程%ld停止生产\n",pthread_self());
            pthread_cond_wait(&cond,&lock);
        }
        num++;
        printf("线程%ld生产了一个商品,当前库存数量为:%d\n",pthread_self(),num);
        pthread_cond_broadcast(&cond);
        pthread_mutex_unlock(&lock);
        sleep(1);
    }
    return NULL;
}

void *sale(void *argv)
{
    while(1)
    {
        pthread_mutex_lock(&lock);
        while(num <= 0)
        {
            printf("库存为0,线程%ld停止销售\n",pthread_self());
            pthread_cond_wait(&cond,&lock);
        }
        num--;
        printf("线程%ld销售了一个商品,当前库存数量为:%d\n",pthread_self(),num);
        pthread_cond_broadcast(&cond);
        pthread_mutex_unlock(&lock);
        int t = rand()%5;
        sleep(t);
    }
}

void closeThread(pthread_t ts[],int len) //声明释放线程的方法
{
    for(int i = 0; i < len; i++)
    {
        pthread_join(ts[i],NULL);
    }
}

int main(int argc, char const *argv[])
{
    srand(time(NULL));

    pthread_mutex_init(&lock,NULL);//初始化互斥锁
    pthread_cond_init(&cond,NULL);//初始化条件变量

    pthread_t ps[3];//声明生产者线程组
    pthread_t ss[5];//声明销售者线程组

    int i;
    for(i = 0; i < 3; i++)
    {
        pthread_create(&ps[i],NULL,produce,NULL);//创建线程并执行
    }
    for(int i = 0; i < 5; i++)
    {
        pthread_create(&ps[i],NULL,sale,NULL);
    }
    
    int plen = sizeof(ps)/sizeof(pthread_t);
    closeThread(ps,plen);//释放生产者线程
    
    int slen = sizeof(ss)/sizeof(pthread_t);
    closeThread(ss,slen);//释放消费者线程
    
    pthread_mutex_destroy(&lock);//释放互斥锁
    pthread_cond_destroy(&cond);//释放条件变量
    return 0;
}
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