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

[Matt Austern]

On Jan 12, 2004, at 11:14 AM, Ted Baker wrote:

>> ... the problem isn't with the model, but rather with the effect of 
>> that
>> model on existing code that all-too-casually and agressively eats
>> exceptions it doesn't understand. I think there are vanishingly few
>> circumstances where a blind catch(...) without an unconditional 
>> re-throw
>> should be considered "legitimate". If you don't completely understand
>> what an exception means, you cannot claim to have completely 
>> recovered,
>> and therefore cannot reasonably finalize propagation. (And when you
>> catch anonymously, you can't possibly understand what they mean since
>> you can't even identify them.) On the other hand, regardless of 
>> whether
>> the semantics are meaningful or reasonable, the syntax is legal and
>> apparently (unfortunately) in common use, so I can't dispute that you
>> need to consider that.
>
> This problem could be eliminated by specifying that cancellation
> is a special case, that cannot be caught by catch(...), i.e., that
> it can only be caught by a handler that names it explicitly, or that
> it cannot be caught at all.

That was originally proposed, and it's a bad idea.  There's too much
code of the form
   catch(...) {
     do_some_partial_cleanup();
     throw;
   }
This is important, and it's recommended style.  Uncatchable
exceptions would be a major change in the C++ exception model.

			--Matt