Linux进程间通信——信号量2，利用信号量实现三个进程a,b,c分别输出“A“,“B“,“C“,要求输出的结果必须是”ABCABCABC...“

多个信号量

三个进程a,b,c分别输出"A","B","C",要求输出的结果必须是"ABCABCABC...";

思路：

代码演示：

//sem.h
typedef union senum
{
    int val;
}SemUn;

int GetSem(int key,int initval[],int n); 
int DelSem(int semid);
int SemP(int semid,int index);
int SemV(int semid,int index);

//sem.c
#include "sem.h"
#include <sys/sem.h>
#include <stdio.h>

int GetSem(int key,int initval[],int n)
{
    int semid=semget((key_t)key,n,0600|IPC_CREAT|IPC_EXCL);
    if(semid==-1)
    {   
        semid=semget((key_t)key,n,0600);
        if(semid==-1)
        {
            printf("semget error!\n");
            return -1; 
        }
    }   
    else
    {   
        int i=0;
        for(;i<n;i++)
        {
            SemUn data;
            data.val=initval[i];
            int res=semctl(semid,i,SETVAL,data);
            if(res==-1)
            {
                printf("semcil error");
                DelSem(semid);
                return -1; 
            }
        }
    }
        return semid;
}

int SemP(int semid,int index)
{
    struct sembuf buf;
    buf.sem_num=index;//第几个信号量S1,S2,S3
    buf.sem_op=-1;
    buf.sem_flg=SEM_UNDO;

    int res=semop(semid,&buf,1);
    if(res==-1)
    {
        printf("semop p error!\n");
        return -1;
    }
    return 0;
}

int SemV(int semid,int index)
{
    struct sembuf buf;
    buf.sem_num=index;//第几个信号量S1,S2,S3
    buf.sem_op=1;
    buf.sem_flg=SEM_UNDO;
    int res=semop(semid,&buf,1);
    if(res==-1)
    {
        printf("semop v error!\n");
        return -1;
    }
    return 0;
}

int DelSem(int semid)
{
    if(semctl(semid,0,IPC_RMID)==-1)
    {
        perror("semctl del error!\n");
        return -1;
    }
    return 0;
}
          

//a.c
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>
#include <unistd.h>
#include "sem.h"

int main()
{
    srand(time(NULL));
    int initval[]={1,0,0};
    int semid=GetSem(1234,initval,3);
    assert(semid!=-1);

    int count=0;
    while(count<5)
    {   
        SemP(semid,0);
        printf("A");
        fflush(stdout);
        int n=rand()%3;
        sleep(n);
        SemV(semid,1);
        count++;
    }   
    exit(0);
}

//b.c
include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>
#include <unistd.h>
#include "sem.h"

int main()
{
    srand(time(NULL));
    int initval[]={1,0,0};
    int semid=GetSem(1234,initval,3);
    assert(semid!=-1);

    int count=0;
    while(count<5)
    {   
        SemP(semid,1);
        printf("B");
        fflush(stdout);
        int n=rand()%3;
        sleep(n);
        SemV(semid,2);
        count++;
    }   
    exit(0);
}

//c.c
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>
#include <unistd.h>
#include "sem.h"

int main()
{
    srand(time(NULL));
    int initval[]={1,0,0};
    int semid=GetSem(1234,initval,3);
    assert(semid!=-1);

    int count=0;
    while(count<5)
    {   
        SemP(semid,2);
        printf("C");
        fflush(stdout);
        int n=rand()%3;
        sleep(n);
        SemV(semid,0);
        count++;
    }   
    DelSem(semid);//最后一个退出的销毁
    exit(0);
}

运行结果：