When a shared data is small enough and you only need to increment it or swap two values, there's an option to do that without locking. All modern processors implement instructions that can do simple operations on memory locations in such a way that another processor can not interrupt the operation in progress.
Such instructions are sometimes called interlocked operations, while the whole idea of programming with them is called lock-free programming or, sometimes, microlocking. The latter term is actually more appropriate, as the CPU indeed does some locking. This locking happens on an assembler instruction level, and is therefore much faster than the operating system-based locking, such as critical sections.
As these ...
