[技術] Linux Semaphores PV操作程式

Written on 8:36 下午 by Yu Lai

From: http://blog.csdn.net/lcrystal623/archive/2007/03/16/1531189.aspx

多程序實現PV操作，子程序為生產者，倉庫可以容納5個物品，每次檢查倉庫是否滿，若不滿則執行P操作，生產一個物品放入倉庫。父程序檢驗倉庫是否空，若不空則消耗一個物品，執行V操作。sleep函數是隨即設置生產或消費所用時間。

程式主要目的是展示Semaphores的使用，以備以後參考。

#include <stdio.h>
#include <stdlib.h>

#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/types.h>

int main()
{
 int semID,ret,num;
 int sleepTime;
 struct sembuf buf;
 
 semID = semget(IPC_PRIVATE,1,0666);
 if(semID < 0)
 {
  printf("建立Semaphores出錯\n");
  exit(1); 
 }
 
 if(fork() == 0)
 {  
  while(1)
  {
   num = semctl(semID,0,GETVAL,NULL);
   if(num < 5)
   {
    sleepTime = rand() % 5;
    sleep(sleepTime);
    
    buf.sem_num = 0;
    buf.sem_op = 1;
    buf.sem_flg = 0;
    
    ret = semop(semID,&buf,1);
    if(ret < 0)
    {
     printf("執行P操作失敗！\n");
     exit(1);
    }
    
    num = semctl(semID,0,GETVAL,NULL);
    printf("生產者生產了一個物品放入了倉庫...倉庫中現有物品%d個\n",num);
   }
  }  
 }
 else
 {
  while(1)
  {
   num = semctl(semID,0,GETVAL,NULL);
   if(num > 0)
   {
    sleepTime = rand() % 5;
    sleep(sleepTime);
    
    buf.sem_num = 0;
    buf.sem_op = -1;
    buf.sem_flg = 0;
    
    ret = semop(semID,&buf,1);
    if(ret < 0)
    {
     printf("執行V操作失敗！\n");
     exit(1);
    }
    
    num = semctl(semID,0,GETVAL,NULL);
    printf("消費者從倉庫中消耗了一個物品...倉庫中現有物品%d個\n",num);
   }
  }
 }

 return 0;
}

Posted in 技術, IPC, Linux

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