4db
Subj : Re: A question about atomic_ptr
To   : comp.programming.threads
From : Peter Dimov
Date : Wed Apr 13 2005 10:33 pm

Joe Seigh wrote:
> On Wed, 13 Apr 2005 18:53:50 +0300, Peter Dimov <pdimov@gmail.com>
> wrote:
>> Joe Seigh wrote:
>>
>>> atomic_ptr/local_ptr is a modified weighted reference counting
>>> scheme.  local_ptr looks a lot like pure weighted reference
>>> counting.
>>
>> From looking at the source, local_ptr doesn't seem weighted to me.
>> There is no weight member and copies just increment a shared
>> reference count (the ephemeral count). But maybe I'm not looking at
>> the latest version (the one on atomic-ptr-plus.sf.net is 0.0.2).
>>
> Copying an atomic_ptr to a local ptr is a tranfer of 1 weighted
> reference count without updating the central reference count. local_ptr 
> orginally weren't copyable since they only have a weight of
> 1 but I added some logic from atomic_ptr to atomic_ptr copying, it's
> just not as efficient.  The extra logic obfuscates the weighted ptr
> logic somewhat so it's hard to see.

I see it now, thank you; there is an ecount in atomic_ptr. But even though I 
understand what the code does, I'm still puzzled as to what this scheme buys 
you.

.

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