From: Joel VanderWerf <vjoel@...>
Date: 2006-02-19T09:00:25+09:00
Subject: Re: Thread#stop

Daniel Sheppard wrote:
> The following probably contains world-destroying race-conditions, but it
> roughly works. Making it work properly is left as an exercise for the
> reader.
> 
> 
> $stoppable = []
> $stop_all = false
> 
> def stop_all
>     $stop_all = true
> end
> 
> def start_all
>     $stop_all = false
>     $stoppable.each {|t| p "waking #{t}"; t.wakeup}
> end
> 
> set_trace_func proc { |event, file, line, id, binding, classname|
>     if $stop_all && $stoppable.include?(Thread.current)
>         p "#{Thread.current} stopping"
>         Thread.stop
>         p "#{Thread.current} restarted"
>     end
> }
> 
> $stoppable << Thread.new {
>     while sleep 1
>         p "child is running"
>     end    
> }
> 
> p "started"
> sleep 5
> p "stopping all"
> stop_all
> sleep 5
> p "starting all"
> start_all
> sleep 5
> p "exiting"
> 

On second thought, this is actually just what I need, with a small
modification: only call set_trace_func when the request to stop comes
in, and then call set_trace_func(nil) when threads are restarted.

For example:

th = Thread.new do
  loop do
    sleep 0.1
    puts "alive!"
  end
end

sleep 0.3

puts "stopping"
stopper = proc {|event, file, line, id, binding, classname|
  Thread.stop if Thread.current == th
}
set_trace_func stopper

sleep 1

puts "starting"
set_trace_func nil
th.wakeup

sleep 0.3

The output is:

alive!
alive!
stopping
starting
alive!
alive!
alive!

(There's about a 1 sec delay between the "stopping" and "starting"
lines, as desired.)

So, thanks for the suggestion, Daniel. I just didn't consider it closely
enough before, because I was scared away by set_trace_func.

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407