From: Joel VanderWerf <vjoel@...>
Date: 2007-05-12T07:08:05+09:00
Subject: Re: basic threading question: can ruby use real threads?

MenTaLguY wrote:
...
>> What if there were two kind of ensure clauses, one which is
>> uninterruptible (to be used only for cleanup that is deterministic) and
>> one which is interruptible (and not guaranteed to finish)?
> 
> Nope, that's still not sufficient.  The fundamental problem is that other threads can _arbitrarily_ mess with control flow by injecting exceptions via Thread#raise.  There's no way to guarantee invariants will be preserved, no matter how clever your ensure implementation is.

But what if we limit that arbitrary power by adding a new construct?

Suppose thread1 is executing this code:

   begin
   ensure_uninterruptible # not in ruby yet
     # quick and deterministic cleanup code
   end

and suppose that thread2 does this:

   thread1.raise

Can't we implement ensure_uninterruptible in such a way that 
thread1.raise waits until thread1 finishes the clause (or maybe raises 
an error in thread2 instead of in thread1)?

I'm not sure it's a good idea, but is there a reason it couldn't be done 
with green threads?

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407