[SOLVED] Signal Handling problem

monicojr84 · 03-04-2011, 06:19 PM

I have a program that creates and uses a shared memory segment. I am trying to find out how to detach and delete this shared memory segment when I hit crtl-C, and I still need the process to terminate.

shmdt() and shmctl() have variables that are local to the main passed to them
(shared and shmid)

Code:

//Prototype
void leave(int sig);

//part of code trying to use signal handling
if(signal(SIGINT, leave))
{ 
  //Deallocate shared memory segment
  shmdt(shared);
	  
  //remove shared memory segment
  shmctl(shmid, IPC_RMID, NULL);
}

//leave declaration
void leave(int sig)
{ 
  sleep(10);
}

JimmyKrak · 03-05-2011, 04:49 AM

It's been a while since I've messed with signals, but it seems that your "signal" call is only to set up your handler association with the specified event. Put your detach and remove within your handler (i.e. "leave"). These actions will happen once the event is captured.

colucix · 03-06-2011, 07:33 AM

Moved: This thread is more suitable in Programming and has been moved accordingly to help your thread/question get the exposure it deserves.

dwhitney67 · 03-06-2011, 07:55 AM

Quote:

Originally Posted by JimmyKrak

It's been a while since I've messed with signals, but it seems that your "signal" call is only to set up your handler association with the specified event. Put your detach and remove within your handler (i.e. "leave"). These actions will happen once the event is captured.

For simple/quick tasks, this may be appropriate, however typically one sets a semaphore (a simple counter or flag) in the signal handler, and then checks the state of this semaphore elsewhere.

Something like this:

Code:

int all_done = 0;

void leave(int signo)
{
   if (signo == SIGINT)
   {
      all_done = 1;
   }
}

int main()
{
   /* This style is obsolete; should be avoided! */
   /* signal(SIGINT, leave); */

   struct sigaction usr_action;
   sigset_t         block_mask;

   sigfillset(&block_mask);

   usr_action.sa_handler = leave;
   usr_action.sa_mask    = block_mask;
   usr_action.sa_flags   = 0;

   sigaction(SIGINT, &usr_action, NULL);

   while (!all_done)
   {
      /* handle task of application... */

      /* perhaps have a delay... */
      usleep(10000);
   }

   /* clean up... */

   return 0;
}