From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2008-08-27T04:37:16+09:00
Subject: Re: open3 and background processes

IO.readlines will try to read out everything until EOF, hence it "hangs" for long running background processes. Can you use IO.readline instead and modify your spawned program to output a one line message to indicate success? Then it will catch both errors and successful runs.

Gennady.

> -----Original Message-----
> From: Daniel Berger [mailto:djberg96@gmail.com]
> Sent: Tuesday, August 26, 2008 12:28 PM
> To: ruby-talk ML
> Subject: open3 and background processes
>
> Hi all,
>
> I've got a poor man's init script where I'm firing off a Ruby process
> in the background if it's not already running.
>
> If the process fails, no problemo. The process I called dies, I pull
> the error from the stderr handle via readlines, and fire off an email
> to myself. But if the process succeeds, IO#readlines hangs because
> there's no data to be read, so it just hangs there waiting for it.
>
> One solution I came up with was to wrap the IO#readlines in a timeout,
> but that feels clunky. Is there a better way to do this?
>
> require 'open3'
> require 'timeout'
>
> program = File.join(Dir.pwd, "miniserver.rb")
>
> cmd = "ruby #{program} &"
>
> Open3.popen3(cmd) do |stdin, stdout, stderr|
>    begin
>       # Better way?
>       Timeout.timeout(2){
>          error = stderr.readlines
>       }
>    rescue Timeout::Error
>      puts "Timeout"
>      break
>    end
>
>    puts error.join("\n") if error
> end
>
> puts "Done"
>
> Where "miniserver.rb" is just a simple loop/print/sleep program. I
> thought there was a way to peek ahead on an IO object to see if any
> data is available on the handle before attempting to read it, but
> perhaps I'm glossing over the appropriate method.
>
> Suggestions?
>
> Thanks,
>
> Dan