Semop returns identifier removed

Question

I am creating a multi-process application with a shared memory segment and a semaphore locking it and signal handlers.

Whenever I lock and unlock my semaphore everything is ok, as long as it is in my main program (or one of the children).

The problem occurs when I am inside a signal handler. There I lock the semaphore, do some updates on the shared memory segment and unlock it.

I have a struct sembuf let's call it sb.

My lock code

void semLock(){
  sb.sem_op=-1;
  semop(sID,sb,sizeof(sb);
}

my unlock code

void semUnlock(){
  sb.sem_op=1;
  semop(sID,sb,sizeof(sb);
}

and how I do my stuff

void signalHandler(int segnum){
  semLock();
  //do some stuff
  semUnlock();
}

There is no real reason why this would not work as sID is global and is inherited to all the children the parent process creates and also when the children are running other code that locks and unlocks the semaphore.

I think the issue is that this is inside a signal handler but I do not understand why. The error that is printed in the terminal is

semop failed identifier removed

I try googling the error but did not find any meaningful or relevant information on what might cause it.

EDIT when I create sb it's initialized with {0,-1,0} I only have one semaphore in my ipcs

Answer 1

As it turns out somewhere in my code I was losing the semaphore ID and semLock and semUnlock were trying to lock and unlock a wrong ID and they were returning an error