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To: Bruce Evans <bde@zeta.org.au>
cc: ache@nagual.ru, brian@awfulhak.demon.co.uk, brian@utell.co.uk,
        current@FreeBSD.org
Subject: Re: ppp 
In-reply-to: Your message of "Tue, 11 Mar 1997 21:50:52 +1100."
             <199703111050.VAA09291@godzilla.zeta.org.au> 
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Date: Tue, 11 Mar 1997 15:44:35 +0000
From: Brian Somers <brian@shift.lan.awfulhak.org>
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> Generally you don't care and can't tell exactly how many signals occurred
> (the system doesn't count them).  One exception might be if SIGALRM is
> pended and there is too large a latrency before unpending.  Then counting
> could be used to tell how many SIGALRMs were mishandled :-).
> 
> The main problems here are:
> 1. the code is non-portable.  sigset_t might be larger than int, and not
>    using sigset_t makes it hard to use sigprocmask().
> 2. `caused &= ~(1<<sig);' might not be atomic.  All signals should be
>    blocked when `caused' is changed.
> 3. Some signals should probably be blocked when the handler is called.
>    See Andrey's old mail.
> 4. Perhaps there should a loop to handle signals that arrive after `had'
>    is initialized.  This depends on how long you can afford to wait
>    before the next call to handle signals.  Some locking may be required.
> 
[.....]
> Bruce

&= ~ isn't guaranteed atomic ?  Yeuch.  I'd tend to go with Andrey's
suggestion that I use an int array rather than a bit array.  I assume
that ++ and -- are guaranteed to be atomic (if they're not, I'm in *lots*
of trouble).

This should solve the above.  The process loop will look something like:

extern int ncaused;  /* The cumulative number of signals caused */
int sig;

while (ncaused) {
    for (sig = 0; sig < __MAXSIG; sig++)
        if (caused[sig]) {
            ncaused--;
            caused[sig]--;
            (*handler[sig])(sig+1);
        }
}

The actual signal trap would of course increment caused[n] and ncaused.


-- 
Brian <brian@awfulhak.demon.co.uk> <brian@freebsd.org>
      <http://www.awfulhak.demon.co.uk>
Don't _EVER_ lose your sense of humour !