Re: Question about threads and signals

From: Ulrich Drepper (
Date: Fri Jan 17 2003 - 22:51:02 EST

Hash: SHA1

Jamie Lokier wrote:

> 1. If a signal is delivered to a thread, is it masked for the duration of
> the handler in (a) just that thread or (b) all threads?


> In other words, if I have 3 threads and SIGIO is not blocked in any
> of them, is it possible for my SIGIO handler to be called up to 3
> times concurrently? Or is the blocked mask somehow shared?

Masks are never shared.

> Is the same thing true of SIGCHLD? SIGSEGV?

Yes. Up to the point where a fatal signal isn't caught and the process
is killed. At that point all threads except the one responsible for the
termination is stopped and then terminated.

> 2. Is this true of POSIX threads in general, or just Linux?

Well, the above is what POSIX requires and what I think we've
implemented. These requirements are essential for programs which do
much of their work in signal handlers. Creating more threads which
mainly just sit around but can react to signals is a valid programming

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