From: Tanaka Akira <akr@...>
Date: 2009-07-27T16:16:05+09:00
Subject: [ruby-core:24570] Re: [Bug #1525] Deadlock in Ruby 1.9's VM caused by ConditionVariable.wait and fork?

In article <4A6C5608.1080202@plan99.net>,
  Hongli Lai <hongli@plan99.net> writes:

> In any case, not being able to create threads or doing anything
> complicated in child processes is a serious limitation. This makes
> forking-without-exec in Ruby 1.9 as good as useless. Even
> forking-with-exec is dangerous now. For example, suppose that the child
> process creates a command string to pass to exec(), and creating this
> command string involves malloc()ing memory. Even this isn't safe anymore.

Even worse, YARV uses a timer thread.  It is an internal
native thread which is always exists.  When Kernel#fork is
used, YARV implicitly start a timer thread in the child
process.  It is dangerous.

Process.spawn helps the forking-with-exec situaion.  It
creates a new process.  Bunch of process attributes are
specifiable but no Ruby script is run in the child process.
So a timer thread is not required in the child process.

I'm not sure we can help forking-without-exec situation.
-- 
Tanaka Akira