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PODiscussion with a sub-process, using Ruby with IO and threading
 

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  1. PODiscussion with a sub-process, using Ruby with IO and threading
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    <p>I am trying to use IO.popen in order to put (with .puts method) and to get (with .gets method) messages from a process to its sub-process.</p> <p>I am not very experimented and I have a question about. Having the following code, I have an error because it is not possible to write in a closed stream.</p> <pre><code>class Interface def initialize(path) @sub_process = IO.popen(path, 'w+') end def start! if ok? @sub_process.puts 'Hello', 'my name is ...' # and more... end end protected def ok? is_ready?(@sub_process) &amp;&amp; is_cool?(@sub_process) end def is_ready?(sub_process) reply = process_command(sub_process, 'are u ready?') reply.chomp.match(/yes_i_am_ready$/) end def is_cool?(sub_process) reply = process_command(sub_process, 'are u cool?') reply.chomp.match(/yes_i_am_cool$/) end def process_command(sub_process, command) rdr = Thread.new { sub_process.read } # alternative: io.readlines sub_process.puts "#{command}" sub_process.close_write rdr.value # joins and fetches the result end end a = Interface.new("./program") a.start! </code></pre> <blockquote> <p>(...) in `write': not opened for writing (IOError)</p> </blockquote> <p>As we can see, this error occur during is_cool? test (as explained at: <a href="http://ruby-doc.org/core/classes/IO.html#M002289" rel="nofollow noreferrer">http://ruby-doc.org/core/classes/IO.html#M002289</a>).</p> <p>But if I try to comment in process_command method the line:</p> <pre><code># sub_process.close_write </code></pre> <p>the script seems to sleep... infinitely :s</p> <p>I believe that it is not possible to open again a closed stream. And I can't create an other IO.popen instance of my program "./program" because it needs to be initialized with some command (like 'are u ready?' and 'are u cool?') at the beginning, before I use it (by sending and receiving messages like a simple discussion).</p> <p>How changes can I do over the current code in order to solve this problem?</p> <p><strong>Edit</strong>: in other words, I would like to establish a such communication (according to a given protocol):</p> <pre><code>Parent message: Child answer: -------------- ------------ 'are u ready?' 'yes_i_am_ready' 'are u cool?' 'yes_i_am_cool' 'Hello' 'foo' 'my name is ...' 'bar' </code></pre> <p>Many thanks for any help.</p>
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    1. USPuru puru rin..
    1. USPuru puru rin..
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    1. COWhat happens if you replace `sub_process.close_write` with `sub_process.flush`?
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      1. USWayne Conrad
    2. COThe parent process seems to wait infinitely. And exit with a Timeout::Error if I use Timeout::timeout(5) { ... }.
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      1. USPuru puru rin..
 

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