Different signal handlers for parent and child

Question

I have a program with a signal handler:

signal(SIGINT, signalhandler);

Then the program forks and the child needs a different signal handler so:

pid = fork();

/* What happens here? */

if(pid==0)
{
signal(SIGINT, signalhandler_for_child);
}

So what happens if a SIGINT is called right after the fork but before the new sign handler is assigned?

Can this happen or there is no possibility to be interrupted before the child gets the new signal handler.

If it is possible. How could I queue the signal to the child so it gets time to get the new handler?

I know that the probabilities, if they exist, must be almost 0, but I want to make sure the application is robust in this aspect.

Answer 1

So what happens if a SIGINT is called right after the fork but before the new sign handler is assigned?

The signal handler installed in the parent will be called. Child process inherits it.

Can this happen or there is no possibility to be interrupted before the child gets the new signal handler.

Cetainly can happen.

If it is possible. How could I queue the signal to the child so it gets time to get the new handler?

To ensure, you need to block SIGINT before calling fork() and then reinstall a different for SIGINT in the child process and then unblock SGINT.

/* block SIGINT here. */

pid = fork();

if (pid == 0) {
    /* Install a new SIGINT handler here. */
    /* Unblock SIGINT. */
    ...
} else if (pid > 0) {
   /* The SIGINT handler is already in place. So just unblock SIGINT. */
   ...
} else {
   /* error */
}

Look at sigprocmask() and pthread_sigmask() for blocking and unblocking signals.

You may also find the GNU documentation on signal blocking useful.