From: bob@... (Bob Proulx)
Date: 2007-09-12T13:04:18+09:00
Subject: Re: Threads and daemons

Cd Cd wrote:
> Okay, bear with this. When I copied the program, I forgot part of it -(
> Here is the entire thing.

I think your "party" process is exiting very quickly.  I think there
is a problem when it is run like this and since the output from the
program is being discarded you are not seeing it.

> #!/usr/local/bin/ruby
> 
> threads=[]
> 
> 4.times do |i|
>         threads[i]=Thread.new do
>         %x{/usr/local/bin/party}

Ouch.  Please think about indention here.  That line should be
indented one more level than the previous line.  And an indention of
eight is pretty big for one level of indention.

>         end
> end
> 
> threads.each{|thr| thr.join}

The %x{} is executing the party program but any output is being
discarded.  Personally I think using 'system' is better in that case
because it does not need to collect the output at all.  Using %x{...}
or using `...` means that ruby needs to wait until the process has
terminated and then do something with the string of output collected.
In this case the do something is nothing and it is garbage collected
but then in that case I think it is better not to collect it at all.

Whenever I see `...` or %x{...} without it being an assignment it
triggers me to question it.

> So do I move join into the do/end block?

Try this modification to your program:

  #!/usr/bin/env ruby
  threads = []
  4.times do
    threads << Thread.new do
      output = %x{/usr/local/bin/party}
      puts "party output: " + output
    end
  end
  threads.each{|thr| thr.join}
  exit 0

Is there any output from your "party" program?  I am hoping there will
be errors shown there that were not displayed before that will lead
you to the problem.

When I create a simply /tmp/testdaemon script like this:

  #!/usr/bin/env ruby
  puts "Hello from testdaemon."
  exit 0

And then run your example like this:

  #!/usr/bin/env ruby
  threads = []
  4.times do
    threads << Thread.new do
      output = %x{/tmp/testdaemon}
      puts "party output: " + output
    end
  end
  threads.each{|thr| thr.join}
  exit 0

Then I see this output:

  party output: Hello from testdaemon.
  party output: Hello from testdaemon.
  party output: Hello from testdaemon.
  party output: Hello from testdaemon.

Bob