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