unix 互斥锁与信号量应用例子

 

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

#define SIZE 3
#define STR_SIZE 20

pthread_mutex_t mutex; //全局变量对main 及 线程函数都可见
sem_t read_sem, write_sem; //全局变量对main 及 线程函数都可见

struct _buf_
{
    char* buf[SIZE];
    int front, rear;
}buffer; //循环队列结构体

void thread(void)
{
    while(1)
    {
        if(0 != sem_wait(&read_sem))
        {
            perror("sem_wait_0");
            exit(1);
        }

        if(0 != pthread_mutex_lock(&mutex))
        {
            perror("pthread_mutex_lock_0");
            exit(1);
        }

        fputs("output characters:\n",stdout);

        fputs(buffer.buf[buffer.front],stdout);

        buffer.front = (buffer.front + 1) % SIZE;

        if(0 != pthread_mutex_unlock(&mutex))
        {
            perror("pthread_mutex_lock_0");
            exit(1);
        }
        if(0 != sem_post(&write_sem))
        {
            perror("sem_wait_0");
            exit(1);
        }

        sleep(10);
    }

}

int main(void)
{
    //初始化循环队列结构体
    int i;
    bufferbuffer.front = buffer.rear = 0;
    for(i=0; i < SIZE; i++)
    {
        buffer.buf[i] =(char*) malloc(STR_SIZE);
    }
    //初始化 互斥锁
    //存在警告 pthread_mutexattr_t mutex_attr = PTHREAD_MUTEX_INITIALIZER;

    if(0 != pthread_mutex_init(&mutex, NULL))
    {
        perror("pthread_mutex_init\n");
        exit(1);
    }

    //初始化信号量

    if(0 != sem_init(&read_sem, 0, 0))//linux进程间的信号共享还未能实现，参数PSHARE为0，而且还没有进行写操作没有数据可读，将参数vaule设置为0，进行阻塞
    {
        perror("sem_init_0\n");
        exit(1);
    }

    if(0 != sem_init(&write_sem, 0, 2))
    {
        perror("sem_init_1\n");
        exit(1);
    }
    //创建两个子线程
    pthread_t thd0,thd1;

    if(0 != pthread_create(&thd0,NULL,(void*)thread,NULL))
    {
        perror("pthread_create_0\n");
        exit(1);
    }

    if(0 != pthread_create(&thd1,NULL,(void*)thread,NULL))
    {
        perror("pthread_create_1\n");
        exit(1);
    }

    //进行写入字符操作
    while(1)
    {
        //写信号量阻塞
        if(0 != sem_wait(&write_sem))
        {
            perror("sem_wait_1");
            exit(1);
        }
        //上互斥锁所进行写入操作
        if(0 != pthread_mutex_lock(&mutex))
        {
            perror("pthread_mutex_lock_1");
            exit(1);
        }

        fputs("pls enter 20 character:\n",stdout);

        //读标准输入文件
        if(NULL == fgets(buffer.buf[buffer.rear],STR_SIZE,stdin))
        {
            perror("fgets\n");
            exit(1);
        }

        if(0 == strncmp("end\n",buffer.buf[buffer.rear],3))
        {
            printf("manual exit successfully\n");
            exit(1);
        }

        buffer.rear = (buffer.rear+1)% SIZE;
        //解互斥锁
        if(0 != pthread_mutex_unlock(&mutex))
        {
            perror("pthread_mutex_lock_1");
            exit(1);
        }

        if(0 != sem_post(&read_sem))
        {
            perror("sem_wait_1");
            exit(1);
        }

        sleep(1);

    }



    return 0;
}