Date: Fri, 11 Jun 2004 00:45:28 -0700 From: Sean McNeil <sean@mcneil.com> To: Daniel Eischen <eischen@vigrid.com> Cc: freebsd-threads@freebsd.org Subject: Re: signal handler priority issue Message-ID: <1086939928.10026.26.camel@server.mcneil.com> In-Reply-To: <Pine.GSO.4.10.10406110242160.26412-100000@pcnet5.pcnet.com> References: <Pine.GSO.4.10.10406110242160.26412-100000@pcnet5.pcnet.com>
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OK, I think I have it figured out....
The problem is, that when the first signal handler, SIGUSR1, is run the
SIGUSR2 signal is blocked. I think this is what Daniel was trying to
say, or I didn't provide enough information for him to catch it. So,
I've fixed the sigaction call to unblock SIGUSR2 while SIGUSR1 is going
and rearranged a few things:
me->stop_info.signal = 0;
me->stop_info.last_stop_count = my_stop_count;
/* Tell the thread that wants to stop the world that this */
/* thread has been stopped. Note that sem_post() is */
/* the only async-signal-safe primitive in LinuxThreads. */
sem_post(&GC_suspend_ack_sem);
#if DEBUG_THREADS
GC_printf2("Waiting for restart #%d of 0x%lx\n", my_stop_count, my_thread);
#endif
/* Wait until that thread tells us to restart by sending */
/* this thread a SIG_THR_RESTART signal. */
if (sigfillset(&mask) != 0) ABORT("sigfillset() failed");
if (sigdelset(&mask, SIG_THR_RESTART) != 0) ABORT("sigdelset() failed");
# ifdef NO_SIGNALS
if (sigdelset(&mask, SIGINT) != 0) ABORT("sigdelset() failed");
if (sigdelset(&mask, SIGQUIT) != 0) ABORT("sigdelset() failed");
if (sigdelset(&mask, SIGTERM) != 0) ABORT("sigdelset() failed");
if (sigdelset(&mask, SIGABRT) != 0) ABORT("sigdelset() failed");
# endif
while (me->stop_info.signal != SIG_THR_RESTART) {
sigsuspend(&mask); /* Wait for signal */
}
There might still be a bug that I'm just hiding. I think that the
problem is while in the handler for SIGUSR1 and someone calls
pthread_kill with SIGUSR2, the signal isn't marked as pending because it
is masked off. It appears to rely on the following behavior:
thread 1 calls pthread_kill for SIGUSR1.
thread 2 enters SIGUSR1 handler and SIGUSR2 is masked.
thread 1 calls pthread_kill for SIGUSR2. signal is set pending as it is
currently masked off.
thread 2 calls sigsuspend thus unblocking SIGUSR2. Signal handler for
SIGUSR2 is called and then sigsuspend in SIGUSR1 handler returns.
Is this correct behavior? Should a pthread_kill of a blocked signal
pend or should it be dropped?
Right now, I've worked around this.
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