std::expected_exception (was: [boost] Re: boost::execution_monitor impl under windows)

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-10-08 09:42:17

Alexander Terekhov wrote:
> Peter Dimov wrote:
> [...]
>> My understanding of the two phase business is as follows:
>>
>> Phase 1: search for a handler;
>> Phase 2: unwind to that handler and invoke it, but only if a handler
>> was
>> found.
>
> Yep.
>
>>
>> Extension: a function that performs phase 1 and returns a bool. No
>> rationale (readily) available. Not sure whether, or why, this is a
>> good idea.
>
> I simply have some code (can't change the interface; too late) that
> I'd like to kind "extend":
>
> void operation() {
>   bool cancel_expected =
>           std::expected_exception<std::thread_cancel_request>();
>   /**/
>   SOME_LOOP {
>     /**/
>     if (cancel_expected) std::test_thread_cancel();
>     /**/
>   }
>   /**/
> }
>
> The problem is that some clients have code that invokes it from
> throw()-
> nothing places like d-tors... and don't {always} disable cancelation.
> ;-)

Right. You want to autodetect whether to operate in a throw mode or a
nothrow mode. This will never work. :-)

The problem is that you can't count on people marking nothrow regions
throw() if you can't count on them using operation() correctly (i.e.
disabling cancelation in nothrow regions.)