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Date: Fri, 4 Jan 2008 14:35:39 -0500 (EST)
From: Daniel Eischen <deischen@freebsd.org>
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To: Ivan Voras <ivoras@freebsd.org>
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Cc: freebsd-threads@freebsd.org
Subject: Re: Threads and signals
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On Thu, 3 Jan 2008, Ivan Voras 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)?

Yes, you don't want to call pthread_mutex_lock() (or really any other
non-async-signal-safe function) from the signal handler.

> How is this solved in general? By recursive mutexes?

You can use sigwait() to wait for the signal and block it in all
other threads, or you can use a pipe and write(2) to the pipe from
the signal handler and have another reader thread handle the request.
I suppose there are other ways, like sem_post().

-- 
DE