1.展示没有互斥的程序

1.1.一个购票系统，有5个线程在购票

#include<iostream>
#include<cstdio>
#include<unistd.h>
#include<pthread.h>int tickets=100;
void* thread_run(void* args)
{int tmp=*((int*)args);while(1){if(tickets>0)//购表{usleep(10000);tickets--;printf("我是%d线程,还剩%d\n",tmp,tickets);}else{printf("没票了\n");break;}}return (void*)0;
}
int main()
{pthread_t tid[5];for(int i=0;i<5;i++)//创建5个线程{int* t=new int(i);pthread_create(tid+i,NULL,thread_run,(void*)t);}for(int i=0;i<5;i++){pthread_join(tid[i],NULL);}return 0;
}

执行结果：不是每次都会产生这样的结果，把票购成负数了不合理

原理：

2.互斥

互斥整个过程：保持临界资源的原子性

pthread_mutex_t lock;//锁

pthread_mutex_init(&lock,NULL);//初始化

pthread_mutex_lock(&lock);//加锁

//临界区

pthread_mutex_unlock(&lock);//解锁

pthread_mutex_destroy(&lock);//删除锁

修改上面代码

#include<iostream>
#include<cstdio>
#include<unistd.h>
#include<pthread.h>pthread_mutex_t lk;//锁
int tickets=100;
void* thread_run(void* args)
{int tmp=*((int*)args);while(1){pthread_mutex_lock(&lk);//加锁if(tickets>0){usleep(10000);tickets--;printf("我是%d线程,还剩%d\n",tmp,tickets);}else{printf("没票了\n");pthread_mutex_unlock(&lk);//解锁break;}pthread_mutex_unlock(&lk);//解锁}return (void*)0;
}
int main()
{pthread_mutex_init(&lk,NULL);//初始化pthread_t tid[5];for(int i=0;i<5;i++){int* t=new int(i);pthread_create(tid+i,NULL,thread_run,(void*)t);}for(int i=0;i<5;i++){pthread_join(tid[i],NULL);}pthread_mutex_destroy(&lk);//删除锁return 0;
}