[boost] Re: shared_ptr and BOOST_DISABLE_THREADS

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2004-04-27 05:37:16

Howard Hinnant wrote:
[...]
> > http://www.pdimov.com/cpp/shared_count_x86_exp2.hpp
> 
> Somehow I think I knew this and had just completely forgotten about it
> (I actually already had your proof of concept implementation
> bookmarked).  Thanks for the reminder!

You're also doing PPC, right? WinXX's InterlockedIncrement, 
InterlockedDecrement, and InterlockedCompareExchange are fully 
fenced (bidirectional "full stop" barrier for loads and stores
imposed on both compiler and hardware). You can do better than 
that. http://google.com/groups?selm=3F17EF6F.97295E7D%40web.de

decrement() shall have the effect of release memory sync 
operation if the resulting value of a reference count is not 
zero; otherwise, this function shall have the effect of 
acquire memory synchronization operation. For compiler that
still means "full stop" but not so for hardware (or whoever
does runtime reodering). increment() doesn't impose any 
reordering constraints. decrement(msync::acq{, ...}) shall 
have the effect of acquire memory sync operation if the 
resulting value of a reference count is zero; otherwise, the 
memory synchronization effect of this function is unspecified. 
decrement(msync::rel{, ...}) shall have the effect of release 
memory synchronization operation if the resulting value of a 
reference count is not zero; otherwise, the memory sync effect 
of this function is unspecified.

regards,
alexander.