[boost] boost::shared_ptr<> uses mutex rather than CAS methods

From: Dayton (mvglen04-cnews_at_[hidden])
Date: 2004-12-09 12:32:05

Shared_ptr<> down deep uses a light-weight mutex to protect the 
increment and decrement of its reference count.  A mutex isn't needed 
here.  A mutex may yield the context of execution.  This seems silly to 
protect a single instruction.

To support threads, all modern processors offer some form of interlocked 
  operation or atomic compare-and-swap instruction.  On SPARC cpus, it 
is the CAS instruction, which acts much like a spin-lock.  Windows 
offers InterlockedIncrement() and InterlocledDecrement() functions, 
which in the newer Microsoft compilers may be compiled as an intrinsic.

I'm a bit allergic to context yielding synchronization objects thrown 
randomly into my server code.  Does anyone know of any reasons to not 
use CAS-style programming here before I propose using it for smart_ptr<>?

Glen