semaphore.c

中科院徐志伟老师一书《操作系统 原理·技术与编程》的源代码和习题接

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <limits.h>
#include <errno.h>
#include <sys/sem.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <string.h>

#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED)
  /* union semun is defined by including <sys/sem.h> */
#else
       /* according to X/OPEN we have to define it ourselves */
  union semun {
        int val;                    /* value for SETVAL */
        struct semid_ds *buf;       /* buffer for IPC_STAT, IPC_SET */
        unsigned short int *array;  /* array for GETALL, SETALL */
        struct seminfo *__buf;      /* buffer for IPC_INFO */
  };
#endif



void main(){
  int semid; 
  pid_t pid,rootpid;
  struct sembuf sop_wait;
  struct sembuf sop_notify;
  union semun arg;
  int i,z,status;
  int n = 5;
  char buf[128],*c;

  if((semid = semget(IPC_PRIVATE,2,0600)) == -1)
  {
    fprintf(stderr,"%s:semget()\n",strerror(errno));
    exit(1);
  }

  arg.val = 1;
  if(semctl(semid,0,SETVAL,arg) == -1){
	perror("semctl(SETALL)");
	exit(1);
  }

   rootpid=getpid();
	
   sop_wait.sem_num = 0;
   sop_wait.sem_op = -1;
   sop_wait.sem_flg = 0;

   sop_notify.sem_num = 0;
   sop_notify.sem_op = 1;
   sop_notify.sem_flg = 0;

   for(i=1;i<n;++i)
	if(pid = fork())  
   		break;
   sprintf(buf,"i:%d cPID:%ld pPID:%ld chPID:%ld\n",i,getpid(),getppid(),pid);
   c = buf;
   z = semop(semid,&sop_wait,1);
   if(z ==-1){
	perror("semop(sop_wait)");
	exit(1);
   }
   while(*c !='\0'){
     fputc(*c,stdout);
     c++;
   }
   fputc('\n',stdout);
   z = semop(semid,&sop_notify,1);
   if(z ==-1){
	perror("semop(sop_notify)");
   }
   wait(&status);
   if(rootpid==getpid())
   	if(semctl(semid,0,IPC_RMID,arg)==-1)
   	{
        	perror("semctl(IPC_RMID)");
        	exit(1);
    	}
   exit(0);
}