[c++-pthreads] cancellation points report failure

[Mark Mitchell]

> I don't like the idea of ever entirely discarding a cancellation.  If 
> a cancellation exception is thrown, caught, and discarded, I would like
> to see it surface again at the next opportunity.  I think that means 
> that, e.g., I/O operations might be allowed in exception-handling code
> being run during the cancellation unwind, but if one of those handlers 
> were to swallow the exception, the next I/O operation would fail or
> throw another cancellation.  The idea is not to let the thread get
> much further without finding cause to bubble up toward the top-level
> caller that knows it's in a thread, and can die gracefully.

I think that is a reasonable idea.  

I would much prefer that to (say) implicitly rethrowing cancellation
exceptions. 

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