From: Charles Oliver Nutter <charles.nutter@...>
Date: 2008-03-22T15:05:53+09:00
Subject: Re: Thread#raise, Thread#kill, and timeout.rb are unsafe

MenTaLguY wrote:
> On Sat, 15 Mar 2008 01:00:49 +0900, Roger Pack <rogerpack2005@gmail.com> wrote:
>> It was the problems with timeout that make me wish we had an
>> EnsureCritical (an Ensure that gets Thread.critical=true set to it
>> before entering it), so that timeouts can end properly.
> 
> Anything using Thread.critical has its own problems, particularly
> when native threads are involved.  It can easily result in deadlocks
> if the running thread inadvertently tries to use something which another
> stopped thread is using (imagine a thread stopped halfway through
> releasing a lock that the ensure block needs to acquire, for example
> -- something which would have worked fine with normal use of locks, but
> becomes a problem once threads can "stop the world").

And to clarify, this problem isn't restricted to native threads...even a 
green-threaded model could deadlock if one thread goes critical while 
other threads are holding unrelated locks.

- Charlie