From: Robert Klemme <shortcutter@...>
Date: 2010-03-02T18:31:19+09:00
Subject: Re: IO.popen with Threads

2010/3/2 Eikichi On <eikichi@ymail.com>:
> Thank you very much for your answer, Robert.  Thanks to your help, I
> could start coding. But I have another little problem and I would
> appreciate your opinion.
>
> Here is the code I used:
>
>    class Test
>      def initialize(program)
>        while isready?(program) && cool?(program)
>          program.puts 'start', 'my name is ...'
>          # ...
>        end
>      end
>
>      protected
>
>      def process_command(program, command)
>        begin
>          rdr = Thread.new { program.read } # alternative: io.readlines
>          program.puts "#{command}"
>          program.close_write
>          rdr.value # joins and fetches the result
>        end
>      end
>
>      def isready?(program)
>        reply = process_command(program, 'isready')
>        reply.chomp.match(/yes_i_am_ready$/)
>      end
>
>      def cool?(program)
>        reply = process_command(program, 'cool')
>        reply.chomp.match(/yes_i_am_cool$/)
>      end
>    end
>
> program = IO.popen("./program", "w+")
>
> a = Test.new(program)
> (...)in `write': not opened for writing (IOError)
>
> As we can see, there is an error when I try to send a message to the
> sub-process because of the closure of the stream
> (http://ruby-doc.org/core/classes/IO.html#M002289).
>
> I believe that it is not possible to open again a closed stream.

Exactly that is the source of your error.

>  Do you
> think a good way is to don't close the stream (except at the very end of
> the Ruby script)? or should it be better to change the current code
> structure?

I would certainly change the structure.  I would put the IO.popen
inside the class since you will be writing a class handling a specific
external program - at least that's what seems to be the case here.

When you close the stream depends on the external program you are
executing.  There is no general rule I can give you here.

Note that if you need to deal with multiple requests and responses
from the external process I believe there are a number of tools around
for that already.  You should be able to find something by searching
for "ruby expect".

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/