From: "Ara.T.Howard" <ahoward@...>
Date: 2004-02-26T09:24:47+09:00
Subject: Re: thread gurus please help...

On Wed, 25 Feb 2004, Ara.T.Howard wrote:

forgot to mention that i have $VERBOSE=nil so i don't see the

  "...fork terminates thread..."

err msg.  i assume that, in this case (forking done in open3) it is OK if that
thread is terminated in the child - it obviously seem to continue running in
the parent...

-a

> 
> 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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