Hi! I think the interface of atomic_count should be done in terms of boost::int32_t instead of long. Currently there are 3 independent implementations for atomic_count: * atomic_count_gcc: uses _Atomic_word (32-bit) * atomic_count_win32: uses BOOST_INTERLOCKED_*, currently defined for windows platforms, works on 32-bit types. * atomic_count_pthreads: uses long; however, because it uses a mutex for synchronization, it could use any type for the counter. The reason for bringing this up comes from experimenting atomic_count on a linux x86_64 box with gcc4 (FC4, in case it matters), where long is a 64-bit type, while the counter is 32-bit. I don't know if this also happens on other 64-bit platforms. Regards, João Abecasis