From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2008-08-29T07:16:53+09:00
Subject: Re: open3 and background processes

> -----Original Message-----
> From: Daniel Berger [mailto:djberg96@gmail.com]
> Sent: Tuesday, August 26, 2008 1:09 PM
> To: ruby-talk ML
> Subject: Re: open3 and background processes
>
>
>
> On Aug 26, 1:37 pm, Gennady Bystritsky <Gennady.Bystrit...@quest.com>
> wrote:
> > 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.
>
> Ah, ok. This seems to work fine:
>
> program = File.join(Dir.pwd, "miniserver.rb")
>
> cmd = "ruby #{program} &"
>
> Open3.popen3(cmd) do |stdin, stdout, stderr|
>    # Use readline, since readlines waits until EOF
>    error = stderr.readline

The problem here is that if your miniserver.rb does not output anything to stderr in case of no error, stderr.readline will hang as well until it gets a newline. What I meant in my previous reply is that miniserver.rb must output something like "SUCCESS" to stderr so that you can test for this in popen3 block:

     error = stderr.readline
     unless error.chomp == "SUCCESS
       # process errors here
       ...
     end

>
>    if error
>       error = [error] << stderr.readlines # Get the rest
>    end
>
>    puts error if error
> end
>
> puts "Done"
>
> Many thanks,
>
> Dan