Re: Error passing function in signal( ... )

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 30 Dec 2010 11:49:47 -0800 (PST)
Message-ID:
<0c11fae2-c8f6-40af-9358-8add5f156772@g26g2000vba.googlegroups.com>
On Dec 30, 7:23 pm, Ian Collins <ian-n...@hotmail.com> wrote:

On 12/31/10 06:27 AM, Dudebot wrote:

On Dec 30, 5:33 am, James Kanze<james.ka...@gmail.com> wrote:

More generally, you probably don't want to, at least if the goal
is to trigger a clean shutdown. You normally can't start
a clean shutdown at just anytime, and signals arrive
asynchronously. The usual solution depends on the application:
for anything multithreaded under Unix, you can create a special
signal handler thread; signals will generate an event which
unblocks the thread, and the thread can start the clean shutdown
(running as a normal thread, and not as a signal handler). For
single threaded processes, the usual solution is just to have
a global sig_atomic_t initialized to zero, set it to one in the
signal handler, and poll it at appropriate moments.


Wow, I learned a lot from this thread--many thanks, all. James, can
you point me to how to create the signal handler thread that you
describe? I think that I get it in principle, but am having a hard
time imagining how to actually do it.


This is drifting into the realm of comp.programming.threads, but it's
really quite simple. You just create a thread that blocks on sigwait()
and mask out signals to the other threads. The Solaris man page has an
example:

http://docs.sun.com/app/docs/doc/816-5167/sigwait-2?l=en&n=1&a=view


And the example only uses Posix functionality---no Solaris
extensions---so it should port easily to most other Linux
platforms. (Not that I can easily verify it at the moment.)

--
James Kanze

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