Re: Re: Draft of generation 2 thread class

From: Tom Becker (voidampersand_at_[hidden])
Date: 2002-01-20 03:09:10

On Sat, 19 Jan 2002 12:02:12 -0500, "David Abrahams" 
<david.abrahams_at_[hidden]> wrote:
>I wasn't. If you're going to make it unsafe to put them on the heap, we
>should prevent dynamic allocation, but the big problem with those techniques
>is that none of them prevent you from embedding the object in another one
>which is allocated on the heap (a /very/ likely case). I take this as
>another strong argument against making it do state-restoration instead of
>counting.

This is the primary argument for having the disable_cancellation 
class use counting. I can't think of any other arguments that are 
very compelling. Allocating disable_cancellation objects on the heap 
is not something that I would do. But if we can make the class 
absolutely bullet-proof for all possible uses, no matter how wacky 
they may be, and it's at a low cost, that's the way to go.

In order to support counting safely, it will need a mutex to protect 
the count. There probably won't be much contention for the counts, so 
a single global mutex for all the counts might be enough. Actually, 
if you can use atomic increment and decrement, you might not even 
need a mutex. Either way, that seems like a very small price to pay 
for eliminating a potential failure mode.

Regards,

   Tom

-- 
Tom Becker                      "Within C++, there is a much smaller and
<voidampersand_at_[hidden]>        cleaner language struggling to get out."
                                                       -- Bjarne Stroustrup