Re: [Boost-users] atomic_count overflow/underflow behaviour

Subject: Re: [Boost-users] atomic_count overflow/underflow behaviour
From: Narcoleptic Electron (narcoleptic.electron_at_[hidden])
Date: 2010-02-23 16:27:02

I would like to add some context to my previous question in case there
is a better solution to my problem that bypasses the question.

On Tue, Feb 23, 2010 at 11:46 AM, Narcoleptic Electron
<narcoleptic.electron_at_[hidden]> wrote:
> What is the behaviour of boost::detail::atomic_count overflow?

Consider a thread-safe, reference-counting base class for objects
pointed to by intrusive pointer, implemented using atomic_count.  The
problem is that the reference count can overflow, and overflowing a
signed long is undefined.

My thought is that perhaps, since atomic_count is implemented on a
platform-by-platform basis, the behaviour on each is defined and can
be taken advantage of (i.e. to roll-back the overflow prior to
throwing the exception).  This would allow me to continue to use
atomic_count::operator++ without requiring locking.

Otherwise, it seems that I would need to lock to make "checking the
value and either incrementing it or throwing" a single transaction.

Alternatively, perhaps there is a better way to solve this problem
that I haven't considered (possibly using undocumented atomic calls).
Any suggestions would be greatly appreciated.