Ask a question about semaphore in Linux

leetow2006 · 2013-03-26 01:27:15

Look:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <error.h>

int main()
{ 
   int semid,i;
   struct semid_ds semds;
   key_t semkey;
   if((semkey=ftok(".",1))<0)
   {
     perror("ftok error");
     exit(1);
   }

   semid=semget(semkey,1,IPC_CREAT |IPC_EXCL | 0660);
   if(semid==-1)
   {
      perror("semget error");
      exit(1);
   }
   if(-1==semctl(semid,0,IPC_RMID,0))
   {
      perror("semctl RMID error");
      exit(1); 
   }
   
   return 0;
}

I find when I execute it at first,it run well,but since then it always
display error "File Exists",but I use command:ipcs -s not find any semaphore.
When I correct semkey=ftok(".",1) to semkey=ftok("/root",1),it always
run well.Why?How to correct it?

ewaller · 2013-03-26 01:30:58

I am sorry, but I am obliged to ask: Is this, perchance, a homework problem ?

Last edited by ewaller (2013-03-26 01:31:17)

leetow2006 · 2013-03-26 02:34:52

It is not homework ,I run it in CentOS

ewaller · 2013-03-26 03:18:49

leetow2006 wrote:

It is not homework ,I run it in CentOS

Okay, er, I will take that at face value. Why do you ask here? I just looked back through your post history and you ask a lot of rather esoteric questions about programming. Interesting, yes. Useful to members of this forum, no. A waste of time to people who respond to you because they want to give back to Arch, yes.

Am I missing something? As a moderator, I am about to close this thread unless you can dissuade me.

Arch Linux

#1 2013-03-26 01:27:15

Ask a question about semaphore in Linux

#2 2013-03-26 01:30:58

Re: Ask a question about semaphore in Linux

#3 2013-03-26 02:34:52

Re: Ask a question about semaphore in Linux

#4 2013-03-26 03:18:49

Re: Ask a question about semaphore in Linux

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