A question on sigwaitinfo based IO mechanism in multithreaded applications.

I am trying to use RT signals to notify me of IO events using RT signals
instead of SIGIO in a multithreaded applications.  I noticed that there was
some discussion on lkml during november 1999 with the subject of the
discussion as "Signal driven IO".  In the thread I noticed that RT signals
were being delivered to the worker thread.  I am running 2.6.10 kernel and
I am trying to use the very same mechanism and I find that only SIGIO being
propogated to the worker threads and RT signals only being propogated to
the main thread and not the worker threads where I actually want them to be
propogated too.  On further inspection I found that the following patch
which I have attached solves the problem.

I am not sure if this is a bug or feature in the kernel.


Roland McGrath <roland@redhat.com> said:

This relates only to fcntl F_SETSIG, which is a Linux extension.  So there is
no POSIX issue.  When changing various things like the normal SIGIO signalling
to do group signals, I was concerned strictly with the POSIX semantics and
generally avoided touching things in the domain of Linux inventions.  That's
why I didn't change this when I changed the call right next to it.  There is
no reason I can see that F_SETSIG-requested signals shouldn't use a group
signal like normal SIGIO does.  I'm happy to ACK this patch, there is nothing
wrong with its change to the semantics in my book.  But neither POSIX nor I
care a whit what F_SETSIG does.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>