While reading a discussion concerning different types of mutexes and guards in Boost, I thought it would be pertinent to highlight another possible approach to implement a multithreading library. In libMAGE (http://libmage.sourceforge.net/), we have a universal lock (unilock) abstraction, that provides a common way for construction of different lock managers (exclusive, read/write and even more complicated ones) with replaceable scheduling strategies. Furthermore, they can be easily adapted to mutex interface and used, for example, in methods of condition objects. /Igor Veresov