[c++-pthreads] Restating the Jason model

[Mark Mitchell]

On Mon, 2004-01-12 at 12:39, Jason Merrill wrote:
> I think this is an appropriate time to restate my proposal.  I think
> there's a fair amount of consensus around these three points:
> 
>  * Cancellation is a normal exception.
>  * If a cancellation exception is destroyed, the cancellation request
>    is re-entered, and acted on again at the next cancellation point.
>  * Cancellation is disabled during unwinding.

Thank you for summing up.

I believe that I would support all elements of your proposal, with the
possible exception of:

> My preference is still to amend the C++ standard to allow stdio functions
> to throw cancellation.

However, I don't see that as a particularly big deal one way or the
other.  The observation has already been made that the goal of
preserving existing C++ code is probably incompatible with introducing
cancellation, although Nathan's ETHREADCANCELLED idea is designed to get
around that.

>  * Should cancellation also be disabled in destructors run during normal
>    execution?  In catch blocks?
> 
> IMO, no and no.

Agreed.

>  * How can C++ code interact with a cancellation exception?
> 
> I think everyone agrees that it should be possible to catch a cancel by
> name.  We still need to specify that name and any additional operations the
> cancel object might support.

Agreed.

>  * What about pthread_exit?
> 
> I'm happy with the g++ status quo whereby destroying a pthread_exit
> exception calls terminate.  Unlike cancellation, the position of a call to
> pthread_exit is deterministic, so the user is responsible for making sure
> that it can propagate.

I have no strong feeling here, but calling "abort" would be fine by me.

-- 
Mark Mitchell <mark at codesourcery.com>
CodeSourcery, LLC