[c++-pthreads] Re: thread-safety definition

[Jason Merrill]

On Sat, 10 Jan 2004 22:19:41 +0100, Wil Evers <wil at bogo.xs4all.nl> wrote:

> Richard Henderson wrote:
>
>> On Fri, Jan 09, 2004 at 07:01:31AM +0100, Wil Evers wrote:
>>
>>>A second exception escaping from a destructor called while unwinding
>>>the stack because of some earlier exception will result in program
>>>termination.
>>>
>>> If catching (and not rethrowing) this second exception breaks the
>>> cancellation machinery, then it is the cancellation machinery - and not
>>> the program in question - that is broken.  In other words: we need a way
>>> to prevent this scenario.
>>  It would be trivial to adjust the c++ runtime to disable cancelation
>> while exceptions are in flight.  That avoids that scenario entirely.
>
> It obviously does.  But does that imply we don't need
> 'catch-and-dont-rethrow' blocks in destructors anymore?

No, of course not; we can get double faults in non-threaded programs.  It
does, however, mean that a cancellation exception will never be caught by
such a block.

>[...]
> I've noticed that some people on this list object to this design, but so
> far, I haven't seen an alternative.  In other words, I think we should be
> prepared for threads that discard cancellation exceptions - which is why
> Nathan's 'sticky cancellation' makes sense to me.

I agree that cancellation should be sticky, and it is in my model as well
as Nathan's.  But I don't think that this particular example would discard
cancellation exceptions.

Jason