From: MenTaLguY <mental@...>
Date: 2008-03-19T02:52:17+09:00
Subject: Re: Thread#raise, Thread#kill, and timeout.rb are unsafe

On Wed, 19 Mar 2008 00:20:54 +0900, ara howard <ara.t.howard@gmail.com> wrote:
>> Probably.  Does anyone have any idea?
> 
> 
> Thread.current.raises do |exception|
>    queue.push exception
> end
> 
> ....
> 
> even_loop do
>    stuff
>    if exception = queue.pop
>      ...
>    end
> end
> 
> seems like it would address a ton of issued without overly
> complicating ruby's internals - just provide an 'on raise' handler.

How do you plan on protecting against non-determinism introduced
by the "on raise" handler?  For example, if queue were a
user-implemented data structure, and the handler fired in the middle
of queue.pop?  If queue.pop is not protected by a lock, there is
potential to corrupt the queue object.  If it is protected by a lock,
there is potential for deadlock.

(This is basically the same issue as asynchronous signal safety.)

I think the only way around this is for the receiving thread to 
explicitly choose moments when it wants to receive any pending
asynchronous exceptions.  Can you think of another way?

-mental