From: Eric Schwartz <emschwar@...>
Date: 2004-08-14T02:31:07+09:00
Subject: timeouts with threads and SIGALRM

Following advice in an old ruby-talk thread (can't remember which one,
offhand), I'm trying to implement a timeout with threads.  The
canonical example was something like:

Thread.new do
  sleep 5
  Process.kill "ALRM", $$
end
begin
.... some stuff ...
rescue SignalException => se
  return FAIL_CODE
end

Well, the problem with that is that the thread keeps executing, and if
the process as a whole takes more than 5 seconds to complete, then the
SIGALRM kills the process.

So fine, thinks I, I'll just stop the thread when I'm done with it.
No problem.  Only I can't figure out how.  I can't call Thread#stop
from outside the thread.  What I finally ended up with was something
like:

rv = nil
Thread.new do
  sleep 5
  Process.kill "ALRM", $$ if rv == nil
end
..... catch SIGALRM if it happens ...
rv = query_some_stuff
....
return rv

I'm not excruciatingly happy about this solution, and I thought I'd
open it up to the Ruby community: What's the best way to do the
equivalent of 'alarm(5)' in C?

-=Eric
-- 
Come to think of it, there are already a million monkeys on a million
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		-- Blair Houghton.