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Date: Mon, 23 Oct 2000 18:13:53 -0400
From: froekjaerf@netscape.net (Flemming Froekjaer)
To: freebsd-questions@freebsd.org
Cc: bright@wintelcom.net
Subject: Re: SIG codes > 128 allowed?
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Alfred Perlstein <bright@wintelcom.net> wrote:
>
> * Flemming Froekjaer <froekjaerf@netscape.net> [001023 12:35] wrote:
> > In signal.h, more precisely the struct __siginfo, si_code is defined as 
an 
> > integer, but the same include file also defines the constant _SIG_MAXSIG, 
> > with a value of 128. Does this mean that FreeBSD won't allow signal codes 
> > above 128, or can you use the whole positive spectrum of an integer?
> > 
> > The reason I ask is that I want to define a sighandler for every thread 
in a 
> > process. As you may know, threads share the parent process' signal 
handlers, 
> > so I'll need a unique signal code for each thread. I anticipate that the 
> > number of threads per process will be about a thousand.
> 
> You'll want to find a better way to dispatch to each thread than to do
> this.  You can use pthread_kill(3) to send a signal to a particular
> thread.

At first I thought I'd overlooked something, but after doing some research 
I've come to the conclusion that this still won't do it. You can send the 
signal to a particular thread, alright, but if more than one thread has 
unblocked that particular signal, it will subsequently be very difficult to 
determine which thread the signal was directed at. Furthermore, the 
process-level signal handler must block the signal in question while handling 
it.
What I aim for is true thread-level asynchronous I/O. I want independant, 
event-driven threads, basically, where each thread has it's own signal 
handler which can be invoked, regardless of process states, at any given time.
Now, if I can safely use signals outside the kernel-defined range, all my 
problems will be solved. I just assign a unique signal - and consequently a 
unique signal handler - to each thread.
I'd love to use processes for this, but I'm afraid those are too costly for 
this application. The need for speed and all that...

Again, thanks for all your help!

\Flemming


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