Re: [boost] I think using spinlocks to simulate an atomicshared_ptr...

From: Talbot, George (Gtalbot_at_[hidden])
Date: 2006-11-16 11:44:52

Thanks for looking at that.  I was also thinking--does
enable_shared_from_this need to have an "enable_atomic_from_this"
version?

That would also imply an atomic_weak type.

--
George T. Talbot
<gtalbot_at_[hidden]>
> -----Original Message-----
> From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]]
> On Behalf Of Peter Dimov
> Sent: Wednesday, November 15, 2006 11:42 AM
> To: boost_at_[hidden]
> Subject: Re: [boost] I think using spinlocks to simulate an
> atomicshared_ptr...
> 
> Sorry for the brief response, no time...
> 
> Talbot, George wrote:
> 
> > 2) Without any sort of 2-pointer-wide atomic assignment in hardware,
> > operator= really looks like this:
> >
> > lock the source pointer
> > make a local copy of it
> > release the source pointer
> >
> > lock the destination
> > set the value of the destination from the copy
> > unlock the destination
> >
> > This won't deadlock, but has to make an extra copy of the pointer
> > locally.
> 
> There's no extra copy. shared_ptr::operator= does:
> 
> shared_ptr( r ).swap( *this );
> 
> and the above does:
> 
> lock source
> shared_ptr tmp( src );
> unlock
> 
> lock dest
> dest.swap( tmp );
> unlock
> 
> so the two are equivalent (modulo spinlock order).
> 
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