signal handler priority issue

[Sean McNeil]

On Thu, 2004-06-10 at 22:29, Daniel Eischen wrote:
> On Thu, 10 Jun 2004, Sean McNeil wrote:
> 
> > On Thu, 2004-06-10 at 21:55, Daniel Eischen wrote:
> > > On Thu, 10 Jun 2004, Sean McNeil wrote:
> > > 
> > > > Here is what I see:
> > > > 
> > > > master thread calls pthread_kill with SIGUSR1 and waits on semaphore.
> > > > other thread gets signal and calls sem_post.  It yields the scheduler.
> > > 
> > > This is fine as long as this thread doesn't get a signal
> > > until after sem_post().  Being signal safe doesn't mean
> > > that other threads can't be scheduled.
> > > 
> > > > master thread gets semaphore and continues on it's way.
> > > > master thread calls pthread_kill with SIGUSR2 and keeps going.
> > > 
> > > It can't keep going if there is a possibility that it can
> > > send the same thread another SIGUSR2.
> > 
> > I don't follow. Sorry.
> 
> If the master thread does:
> 
> 	for (i = 0; i < 4; i++) {
> 		pthread_kill(slave, SIGUSR1);
> 		sem_wait(&slave_semaphore);
> 		pthread_kill(slave, SIGUSR2);
> 	}
> 
> You can see that there is a potential race condition where
> the slave thread gets SIGUSR1 and SIGUSR2 very close together.
> It is even possible to get them together in one sigsuspend()
> (if they are both unmasked in the suspend mask).
> 
> You could fix the race by blocking SIGUSR1 from within
> the signal handler (like I described in my last email).

I take it then that when a signal handler is invoked that it's signal
isn't masked while running.  It isn't like a standard hardware interrupt
then.  I'm trying as you suggest and will post results.