Re: first sight

From: bill_kempf (williamkempf_at_[hidden])
Date: 2002-01-16 18:20:48

--- In boost_at_y..., "terekhov" <terekhov_at_d...> wrote:
> --- In boost_at_y..., "bill_kempf" <williamkempf_at_h...> wrote:
> > --- In boost_at_y..., "Peter Dimov" <pdimov_at_m...> wrote:
> > > From: "bill_kempf" <williamkempf_at_h...>
> > > > --- In boost_at_y..., "Peter Dimov" <pdimov_at_m...> wrote:
> > > > > A programmer that wants to catch the cancellation exception 
> may 
> > > > have good
> > > > > reasons to do so. In particular, letting an exception 
escape 
> > from a
> > > > > destructor during stack unwinding terminates the process, 
no 
> > > > questions
> > > > > asked. ;-)
> > > > 
> > > > That's not a reason to catch the request, it's a reason to 
> > DISABLE 
> > > > requests.  A cancellation "exception" can be uncatchable and 
> > still be 
> > > > safe in cases such as this.
> > > 
> > > So, code that currently has
> > > 
> > > try
> > > {
> > > // ...
> > > }
> > > catch(...)
> > > {
> > > // eat exceptions, we're in a destructor
> > > }
> > > 
> > > will need to be fixed to disable cancellation as well.
> > 
> > Only if it makes calls to any "cancellation points".
> 
> Such as thread-shared data access, mutex locking?

I'm still trying to determine what should be a cancellation point and 
what shouldn't.  That's why I'd really appreciate your writing up the 
pros/cons of having the mutex lock be a cancellation point.  I'm 
fairly certain it shouldn't be, but at the very least I'll have to 
document the rationale behind that decision.

> Also, with respect to auto_rethrow_exception:
> 
>  scoped_lock lock( systemWideMutex );
> 
>  beginUpdates(); // modify something; nothrow
> 
>  try
>  {
>     // ... plug-in oper ;-) strong
>  }
>  // ...
>  catch(...)
>  {
>     // ...
>  }
> 
>  finalizeUpdates(); // final modifications; nothrow
> 
>  return;

Such code isn't exception safe any way.  I don't find that to be a 
compelling argument.

In other words, "finalizeUpdate" needs to be either in a RAII 
mechanism or placed in the catch(...).

Bill Kempf