[boost] Re: boost::execution_monitor impl under windows

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2003-10-08 09:12:22

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. ;-)

> 
> This doesn't play well with exception specifications since, 

Those are pretty much broken anyway. 

http://groups.google.com/groups?selm=m.collett-E982F8.12450216072002%40lust.ihug.co.nz
http://groups.google.com/groups?threadm=3D3547BE.3045A2A6%40web.de
(Subject: Re: Is internal catch-clause rethrow standard?)

>                                                             if I understand
> them correctly, (and I have no reason to, since I've never used one or seen
> one used,) a violated exception specification is required to unwind, _then_
> call unexpected(), which can then rethrow a different, "conforming",
> exception.

That needs some fixing, right. std::unexpected() shall be invoked at 
throw point (as kinda "side effect" of throw-expression).

> 
> It also implies that catch(...) should never, ever, be used with a rethrow
> as a "finally", since it deceives phase 1. I'm not sure whether this is
> going to work.

Yeah. Note that catch(...)/rethrow is totally broken "attached" exception 
cleanup handler. Something like "action_on_propagation_of(...)" is the way 
to go. http://groups.google.com/groups?selm=3D6E31E9.33C28525%40web.de

regards,
alexander.