进程间互斥与同步

实验题目：进程间的互斥与同步
实验内容：编写算法，实现进程间对临界资源的互斥访问以及进程间的同步关系
实验要求：
    1、要求进程互斥使用文本文件；
    2、假定文本文件txt1最大可写入30个字符；
    3、写满后复制进程将文本文件的内容复制到另一个文本文件txt2中（无长度限制）。
    4、复制进程复制完毕写入进程可再重新写入， 重复执行3，4，直到给出停止命令。
    5、实现进程间的同步和互斥。

–更新临界区控制，mutex–
- code:

#include
#include
#include
#include
#include//信号量
#include
using namespace std;
typedef union _semnu{
    int val;
    struct semid_ds *buf;
    ushort *array;
}semun;
//v操作
void v(int &sem_id)
{
    struct sembuf sem_b;
    sem_b.sem_num=0;
    sem_b.sem_op=1;
    sem_b.sem_flg=SEM_UNDO;
    if(semop(sem_id,&sem_b,1)==-1)
    {
        cout<<"error"<        exit(0);
    }
}
//p操作
void p(int &sem_id)
{
    struct sembuf sem_b;
    sem_b.sem_num=0;
    sem_b.sem_op=-1;
    sem_b.sem_flg=SEM_UNDO;
    if(semop(sem_id,&sem_b,1)==-1)
    {
        cout<<"error"<        exit(0);
    }
}
//设置信号量初值
void set(int sem_id,int val=1)
{
    semun sem_un;
    sem_un.val=val;
    if(semctl(sem_id,0,SETVAL,sem_un)==-1)
    {
        if(errno==EEXIST)
          cout<<"exist"<      cout<<"set"<"error"<      exit(0);
    }
}
void del(int sem_id)
{
    semun sem_un;
    if(semctl(sem_id,0,IPC_RMID,sem_un)==-1)
      cout<<"error"<}
int main()
{
    //互斥量
    int sem_mutex=semget((key_t)8888,1,IPC_CREAT);
    set(sem_mutexk,1);

    int sem_full=semget((key_t)1234,1,IPC_CREAT);
    cout<    //set semaphore full
    set(sem_full,0);
    int sem_empty=semget((key_t)1235,1,IPC_CREAT);
    cout<    //set semaphore emtpy
    set(sem_empty,1);
    FILE *fp1=fopen("./txt1","w");
    FILE *fp2=fopen("./txt1","r");
    FILE *fp3=fopen("./txt2","w");

    pid_t id=fork();
    if(id>0)//parent
    {
        //produce
        //p(empty)
        //
        //v(full)
        for(int i=0;i<5;i++)
        {
            p(sem_empty);
            p(sem_mutex);//锁定临界区
            cout<<"writing... "<            fseek(fp1,0,SEEK_SET);
            fputs("QWERTYUIOPASDFGHJKLZXCVBNM1234",fp1);
            fflush(fp1);
            sleep(1);
            cout<<"write done"<            v(sem_mutex);
            v(sem_full);
        }
        fclose(fp1);
        cout<<"txt2:"<        system("cat txt2 \n");
    }else if(id==0)
    {
        //consume
        //p(full)
        //
        //v(empty)

        char buf[32];
        buf[31]='\0';
        fill(buf,buf+20,0);
        for(int i=0;i<5;i++)
        {
            p(sem_full);
            p(sem_mutex);//锁定临界区
            cout<<"reading... "<            fseek(fp2,0,SEEK_SET);
            fgets(buf,30,fp2);
            fputs(buf,fp3);
            fflush(fp3);  //由于缓冲方式的影响，30个字符不会立刻读取到buf中，需要fflush
            cout<            cout<<"read done"<            cout<            sleep(1);
            v(sem_mutex);
            v(sem_empty);
        }
        fclose(fp2);
        fclose(fp3);
        exit(0);
    }else//error
    {

        cout<<"创建子进程失败!"<        exit(0);
    }
// del(sem_full);
// del(sem_empty);
    return 0;
}

• output:

//注意要以root用户运行程序

    196608
    229377
    writing...             0
    write done
    reading...             0
    QWERTYUIOPASDFGHJKLZXCVBNM123
    read  done

    writing...             1
    write done
    reading...             1
    QWERTYUIOPASDFGHJKLZXCVBNM123
    read  done

    writing...             2
    write done
    reading...             2
    QWERTYUIOPASDFGHJKLZXCVBNM123
    read  done

    writing...             3
    write done
    reading...             3
    QWERTYUIOPASDFGHJKLZXCVBNM123
    read  done

    writing...             4
    write done
    txt2:
    reading...             4
    QWERTYUIOPASDFGHJKLZXCVBNM123
    read  done