From: Robert Klemme <shortcutter@...>
Date: 2007-05-08T18:35:11+09:00
Subject: Re: threads output/execution question

On 08.05.2007 04:14, tiberiu.motoc@gmail.com wrote:
> Hi,
> 
> I have a ruby multi-threaded application and I don't understand its
> behaviour. I hate just dumping code in a post and asking questions,
> but I cannot explain the problem otherwise. In the code below, I have
> a loop which requests user input to either start/stop a job. The
> execution of the job will happen in a separate thread, because the job
> can terminate unexpectedly. What I don't understand in the code, is
> why doesn't the application just print "Job.start" and
> "'DummyThreads.start" after 5 seconds in the same standard output
> screen (as where it is receiving input). It is not even about the
> screen (I tried putting STDOUT.flush after every puts statement), the
> code is not even executed until I subsequently call DummyThreads
> again.
> 
> So, what I get is:
> Enter option: 1
> [...more than 5 seconds passed...]
> Enter option: 1
> [...immediately...]
> Job.start
> DummyThreads.start
> Enter option:
> [...]
> 
> What I expected is:
> Enter option: 1
> Enter option:
> [...after 5 seconds...]
> Job.start
> DummyThreads.start
> [...]
> 
> Thanks,
> Tiberiu
> 
> PS. here is my code
> 
> class Job
>   def run
>     sleep 5
>     puts 'Job.start'
>   end
>   def kill
>     sleep 5
>     puts 'Job.stop'
>   end
> end
> 
> class DummyThreads
>   def initialize
>     @job = Job.new
>   end
>   def start
>     t = Thread.new { @job.run; puts 'DummyThreads.start' }
>     t.join
>   end
>   def stop
>     t = Thread.new { @job.kill; puts 'DummyThreads.stop' }
>     t.join
>   end
> end
> 
> # create DummyThreads
> dummythreads = DummyThreads.new
> 
> # get user input
> puts 'Enter option: '
> STDOUT.flush
> while option = gets
>   case option.to_i
>     when 1: t = Thread.new { dummythreads.start }
>     when 2: t = Thread.new { dummythreads.stop }
>     when 0: break
>   end
>   puts 'Enter option: '
>   STDOUT.flush
> end
> 

IMHO you have too many threads in there.  Try this for an alternative:

	robert

class Job
   class JobTermination < Exception; end

   def run
     @thread = Thread.current
     begin
       puts 'Job.start'
       work
       puts 'Job.finish'
     rescue JobTermination
       puts 'Job.killed'
     ensure
       @thread = nil
     end
   end
   def kill
     puts 'Job.stop'
     @thread.raise JobTermination if @thread
   end

   private
   def work
     sleep 5
   end
end

class DummyThreads
   def initialize
     @job = Job.new
   end
   def start
     puts 'DummyThreads.start'
     Thread.new { @job.run  }
   end
   def stop
     @job.kill
     puts 'DummyThreads.stop'
   end
end

# create DummyThreads
dummythreads = DummyThreads.new

# get user input
puts 'Enter option: '
STDOUT.flush
while option = gets
   case option.to_i
     when 1: dummythreads.start
     when 2: dummythreads.stop
     when 0: break
   end
   puts 'Enter option: '
   STDOUT.flush
end