Date: Sun, 21 Mar 2010 13:07:50 -0400 (EDT) From: Daniel Eischen <deischen@freebsd.org> To: Pierre-Luc Drouin <pldrouin@pldrouin.net> Cc: freebsd-threads@freebsd.org Subject: Re: Portable Conditional Wait for Inter-Process? Message-ID: <Pine.GSO.4.64.1003211246350.5093@sea.ntplx.net> In-Reply-To: <4BA64260.5000009@pldrouin.net> References: <4BA64260.5000009@pldrouin.net>
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On Sun, 21 Mar 2010, Pierre-Luc Drouin wrote: > Hi, > > I am looking for a portable solution to put a process into a timed wait (a la > pthread_cond_timedwait) such that it can be waken up by another process using > something similar to pthread_cond_broadcast (there might be many waiters). I > guess shared pthread condition variables are not supported by FreeBSD, right? > Is there a portable way to do this? The only solution I can think of right > now is to use alarm and sigwait on the waiters side and kill(wpid,SIGCONT) > on the other side with a list of pids. Yeah, shared mutexes and CVs are not yet supported by FreeBSD. You can use sigtimedwait() to conditionally sleep and kill on the other side, but with caveats: o Only one thread per process can be woken with sigwait() and friends o You must ensure that no other threads (other than the waiter) have the "wake" signal unmasked. You might consider using killpg() to send a signal to multiple processes in a process group. FreeBSD current (9.0) recently added support for shared semapores, so you could give those a try. You might be able to use sem_timedwait() instead of pthread_cond_timedwait() depending on your needs, but you are limited to waking only one thread at a time via sem_post(). You could also have a pipe or domain socket between the sender and each waiting processes. I suppose you could use aio_write() on the sender side to write to selected file descriptors with one operation. The waiters would be using poll() or select() with a timeout. -- DE
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