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<iostream>#include<cstdio>#include<cstdlib>#include<unistd.h>#include<sys/sem.h>//信号量#include<errno.h>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"<<endl;        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"<<endl;        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"<<endl;      cout<<"set"<<val<<"error"<<endl;      exit(0);    }}void del(int sem_id){    semun sem_un;    if(semctl(sem_id,0,IPC_RMID,sem_un)==-1)      cout<<"error"<<endl;}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<<sem_full<<endl;    //set semaphore full    set(sem_full,0);    int sem_empty=semget((key_t)1235,1,IPC_CREAT);    cout<<sem_empty<<endl;    //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...             "<<i<<endl;            fseek(fp1,0,SEEK_SET);            fputs("QWERTYUIOPASDFGHJKLZXCVBNM1234",fp1);            fflush(fp1);            sleep(1);            cout<<"write done"<<endl;            v(sem_mutex);            v(sem_full);        }        fclose(fp1);        cout<<"txt2:"<<endl;        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...             "<<i<<endl;            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<<buf<<endl;            cout<<"read  done"<<endl;            cout<<endl;            sleep(1);            v(sem_mutex);            v(sem_empty);        }        fclose(fp2);        fclose(fp3);        exit(0);    }else//error    {        cout<<"创建子进程失败!"<<endl;        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