操作系统实验之信号量的实现和应用

来源：互联网发布：手机知乎怎么注册编辑：程序博客网时间：2024/06/10 04:51

1.首先复习了下，关于信号量的基本知识，我知道的借口基本有三套了，但是主要的都是解决PV操作，P为：等待，如果信号量不为0，即减1，如果为0的话，即进入等待，V：唤醒P操作等待的线程或者是进程，下面是实验中使用的接口：

//初始化sem_t *sem_open(const char *name, unsigned int value);//P操作int sem_wait(sem_t *sem);//V操作int sem_post(sem_t *sem);//释放int sem_unlink(const char *name);

2）下面是自己写的生产者和消费者测试代码，注意在编译的时候，需要链接：-lpthread

#include <stdio.h>#include <stdlib.h>#include <semaphore.h>#include <sys/sem.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <sys/stat.h>#include <sys/types.h>//联系模型生产者和消费者模型//实现一个进程负责生产，N个进程负责消费#define BUFFER_SIZE 10sem_t* empty;sem_t* full;sem_t* mutex;int main(void){    int fd_file = open("pc.log",O_CREAT|O_RDWR,0644);        empty = sem_open("empty",O_CREAT,0644,10);    full  = sem_open("full",O_CREAT,0644,0);    mutex = sem_open("mutex",O_CREAT,0644,1); //可以进行生产    //将文件大小设置为0    ftruncate(fd_file,0);    //如果有这些信号量的话，先释放    sem_unlink("empty");    sem_unlink("full");    sem_unlink("mutex");    if(!fork())    {    //child  producer        int i = 0;    while(i < 500)        {        i++;        sem_wait(empty);        sem_wait(mutex);            // write the data to file        lseek(fd_file,0,SEEK_END);        write(fd_file,&i,sizeof(i));            sem_post(mutex);        sem_post(full);    }       while(1);    }    if(!fork())    {    int result = 0;    int tmpResult = 0;    int fileLen = 0;        int j = 0;    //consumer    while(1)    {        sem_wait(full);        sem_wait(mutex);        //读取数据，同时将数据删除，从头开始读            lseek(fd_file,0,SEEK_SET);        read(fd_file,&result,sizeof(result));        printf("%ld:%d\n",getpid(),result);        // delete data from file        fileLen = lseek(fd_file,0,SEEK_END);        for(j = 1; j < fileLen/sizeof(result);j++)        {        lseek(fd_file,j*sizeof(result),SEEK_SET);           read(fd_file,&tmpResult,sizeof(tmpResult));        lseek(fd_file,(j - 1)*sizeof(result),SEEK_SET);            write(fd_file,&tmpResult,sizeof(tmpResult));        }        ftruncate(fd_file,fileLen - sizeof(result));        sleep(1);        sem_post(mutex);        sem_post(empty);        }    }    if(!fork())    {        int result = 0;    int tmpResult = 0;    int fileLen = 0;        int j = 0;    while(1)    {       //consumer        sem_wait(full);        sem_wait(mutex);        //读取数据，同时将数据删除，从头开始读            lseek(fd_file,0,SEEK_SET);        read(fd_file,&result,sizeof(result));        printf("%ld:%d\n",getpid(),result);        // delete data from file        fileLen = lseek(fd_file,0,SEEK_END);        for(j = 1; j < fileLen/sizeof(result);j++)        {        lseek(fd_file,j*sizeof(result),SEEK_SET);           read(fd_file,&tmpResult,sizeof(tmpResult));        lseek(fd_file,(j - 1)*sizeof(result),SEEK_SET);            write(fd_file,&tmpResult,sizeof(tmpResult));        }        ftruncate(fd_file,fileLen - sizeof(result));        sleep(1);        sem_post(mutex);        sem_post(empty);        }    }    wait(NULL);}

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