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这是我的操作系统实验课的实验之一，实验要求“实现生产者和消费者程序”。

老师给了我们示例程序，要求我们自己修改调试。程序代码如下，已经在本地linux系统上能够正确运行。

p是模拟生产者，c是模拟消费者，q是退出

但是有一点，如果不是用q退出而是中途用ctrl+c的话，再次运行程序就是显示"segment:File exists"

解决的方法是：

ipcs -s 显示已存在的信号量

ipcrm -s 删除指定信号量

#include	
   
    #include	
    
     #include	
     
      #include	
      
       #include	
       
        #include	
        
         #include 
         
          #include "shmpc.h"/* ******************************************************************************** * Name: main * Description: entry point ******************************************************************************** *///var used to shared memoryint shmid;void *myshm;struct myshm_st *buf;//var used to semaphoreint semid;//common varint i,n;void producer(){ printf ( "Create a Producer Process Success,%d\n",getpid()); //attach share memory myshm=shmat(shmid,NULL,0); if(myshm==(void *)-1) { perror("shmat"); exit(-1); } buf=(struct myshm_st *)myshm; //produe a product for(n=0;n
          
           m_count==BUFSIZE) { printf("[%d/P/%d]:Blocked!\n",getpid(),n); sleep(5); } //P struct sembuf action; action.sem_num=0; action.sem_op=-1; action.sem_flg=SEM_UNDO; if(semop(semid,&action,1)==-1) { perror("semop"); exit(0); } buf->m_count++; buf->m_buf[buf->m_in]='A'; sleep(1); buf->m_in=(buf->m_in+1)%BUFSIZE; printf("[%d/P/%d]:",getpid(),n); for(i=0;i<10;i++) { if(buf->m_buf[i]=='A') printf("|A"); else printf("| "); } printf("|\n"); //V action.sem_op=1; if(semop(semid,&action,1)==-1) { perror("semop"); exit(0); } sleep(DELT); } if(shmdt(myshm)==-1) perror("shmdt"); exit(0);}void consumer(){ printf ( "Create a Consumer Process Success,%d\n",getpid()); //attach share memory myshm=shmat(shmid,NULL,0); if(myshm==(void *)-1) { perror("shmat"); exit(-1); } buf=(struct myshm_st *)myshm; //consum a product for(n=0;n
           
            m_count==0) { printf("[%d/C/%d]:Blocked!\n",getpid(),n); sleep(5); } //P struct sembuf action; action.sem_num=0; action.sem_op=-1; action.sem_flg=SEM_UNDO; if(semop(semid,&action,1)==-1) { perror("semop"); exit(0); } buf->m_count--; buf->m_buf[buf->m_out]=' '; buf->m_out=(buf->m_out+1)%BUFSIZE; printf("[%d/C/%d]:",getpid(),n); for(i=0;i<10;i++) { if(buf->m_buf[i]=='A') printf("|A"); else printf("| "); } printf("|\n"); //V action.sem_op=1; if(semop(semid,&action,1)==-1) { perror("semop"); exit(0); } sleep(DELT); } if(shmdt(myshm)==-1) perror("shmdt"); exit(0);}int main(int argc, char *argv[]){ char t; int ppid,cpid; //create a shared memery printf("Begin...\n"); shmid=shmget(MYKEY,sizeof(struct myshm_st),IPC_CREAT|0770); if( shmid==-1 ) { perror("shmget"); exit(-1); } //attach shared memory myshm=shmat(shmid,NULL,0); if(myshm==(void *)-1) { perror("shmat"); exit(-1); } //init shared memory buf=(struct myshm_st *)myshm; buf->m_count=0; buf->m_in=0; buf->m_out=0; //create a semaphore semid=semget(MYKEY,1,IPC_CREAT|IPC_EXCL|0770); if( semid==-1 ) { perror("semget"); exit(0); } union semun init_val; init_val.val=1; if( semctl(semid,0,SETVAL,init_val )==-1) { perror("semctl"); exit(0); } for(;;) { t=getchar(); switch ( t ) { case 'p' : //create a producer process ppid=fork(); if( ppid==0 ) { producer(); } break; case 'c': cpid=fork(); if( cpid==0 ) { consumer(); } break; case 's': //please add stat code here case 'q': if(shmdt(myshm)==-1) perror("shmdt"); if(shmctl(shmid,IPC_RMID,0)==-1) perror("shmctl"); if(semctl(semid,1,IPC_RMID,NULL)==-1) perror("semctl"); exit(0); } }}
           
          
         
        
       
      
     
    
   

shampc.h

/* *    Description  limited buffer */#define BUFSIZE 10#define MYKEY	9000#define MUTEX	9001#define FULL	9002#define EMPTY	9003#define NSIZE   5	//number of item each child #define DELT	1	//interval between two itemstruct myshm_st{	int m_count;	int m_in;	int m_out;	char m_buf[BUFSIZE];};union semun{	int              val;    /*  Value for SETVAL */	struct semid_ds *buf;    /*  Buffer for IPC_STAT, IPC_SET */	unsigned short  *array;  /*  Array for GETALL, SETALL */	struct seminfo  *__buf;  /*  Buffer for IPC_INFO					  (Linux-specific) */};