From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2004-02-26T09:04:47+09:00
Subject: thread gurus please help...


following is a _simulation_ of a rather complex gui i'm working on.  the gui
run a procedure which, itself, is communication with many other processes via
Open3::popen3 (i _need_ the stderr)... anyhow, i'm having fits getting the gui
to update and do all the io (select/read, etc).  this code seems to work fine
but i am very conerned that something might bite me later... if anyone would
care to comment on the interactions between the io and threads and if this is
a reccomended approach i'd love to hear it... remember this code might look a
bit funny but it demonstrative of what my code actually does.  thanks in
advance for any help/advice

==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ====
require 'tk'
require 'open3'
require 'io/wait'
require 'io/nonblock'
require 'thread'
$VERBOSE=nil
STDOUT.sync = STDERR.sync = true
Thread.abort_on_exception = true

threads = []

#setup gui
root = TkRoot.new
label_a=TkLabel.new root, :text=>'label_a'
label_b=TkLabel.new root, :text=>'label_b'
label_a.pack
label_b.pack

# start the gui running
threads <<
  Thread.new{ Tk.mainloop }

# simulation of my processing loop - which is communcating with another
# process and updating a widget with it's output
def update label, program
  command="ruby -e '#{ program }'" 
  i,o,e = Open3::popen3 command
  i.close

  # we run in a thread so entire process is not blocked on io
  # we DO need to wait for it to complete though, because in the real code i
  # depend on values which are returned...
  Thread.new do
    o_done = false
    e_done = false
    loop do
      rios, = select [o, e], nil, nil
      rios.map do |rio|
        break if o_done and e_done
        if rio.eof?
          rio == o ? o_done = true : e_done = true
          next
        end
        # i like this better, but it hangs
        # putting a critical section results in deadlock
        # a semaphore is too slow...
        #rio.nonblock{ text = rio.read }

        # less elegant but works...
        text = ''
        sleep(0.42) and Thread.pass until rio.ready?
        text << rio.getc while rio.ready?
        label.configure :text=>text
      end
    end
  end.join
end


# start background processing which will update the labels
threads <<
  Thread.new{
    update label_a, '4.times{p Time.now; sleep 1}'
  }
threads <<
  Thread.new{
    update label_b, '4.times{|i| p "foobar_#{ i }"; sleep 1}'
  }

# wait for everyone to finish
#threads.map{|t| t.join}
sleep
==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== ====

-a
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