From: Tanaka Akira <akr@...>
Date: 2012-08-29T17:30:46+09:00
Subject: Re: Is calling system() from a thread suppose to be safe?

2012/8/25 Raúl Gutiérrez Segalés <rgs@rieder.net.py>:

> Sure, here is the full-script:
>
> http://www.itevenworks.net/~rgs/ruby/wifi-state-observer
>
> system() happens inside vpn_down(). As you can see the main thread is
> glib2 loop and the other forks/execs a binary (that connects to a
> vpn).

It seems Process.waitall takes the child process spawned by system().

In my environment, the problem can be reproducible as follows,
sometimes (not always):

  % ruby -ve '
  Thread.new { loop { p Process.waitall } }
  loop { p system("true") }
  '
  ruby 2.0.0dev (2012-08-15 trunk 36702) [x86_64-linux]
  -e:3: warning: instance variable status not initialized
  -e:3:in `system': no implicit conversion from nil to integer (TypeError)
	  from -e:3:in `block in <main>'
	  from -e:3:in `loop'
	  from -e:3:in `<main>'

How about avoiding Process.waitall?

I feel the error message can be improved, though.
-- 
Tanaka Akira