Date: Thu, 3 Jan 2008 17:18:21 -0800 From: Alfred Perlstein <alfred@freebsd.org> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-threads@freebsd.org Subject: Re: Threads and signals Message-ID: <20080104011821.GD76698@elvis.mu.org> In-Reply-To: <fljin9$crb$1@ger.gmane.org> References: <fljin9$crb$1@ger.gmane.org>
next in thread | previous in thread | raw e-mail | index | archive | help
* Ivan Voras <ivoras@freebsd.org> [080103 13:03] wrote: > Hi, > > How do threads interact with signals? In particular, if I have a "main" > process thread (the one started by main()) which generates items for a > mutex-protected queue which are consumed by a worker thread, and I need > to insert an item in the queue from the signal handler, am I correct > that doing pthread_mutex_lock() from the signal handler could deadlock > if the signal handler is executed by any of the threads (and the mutex > is non-recursive)? > > How is this solved in general? By recursive mutexes? You need to block/unblock signals or use sigwait. So basically your code will look something like: main() { defer_signals(); signal(SIGWHATEVER, &handler); make_threads(); for ( ;; ) { do_stuff(); undefer_signals(); /* right here "handler" may be called */ defer_signals(); } } Another option is to have one of your threads use sigwait() and do the operation synchronously. Another is to write(2) to a pipe(2) from within your signal handler that one of your threads is select(2)/poll(2)/kevent(2) against, then the selecting thread can read the byte, thereby clearing the event and then queue the workitem synchronously. -- - Alfred Perlstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20080104011821.GD76698>