Building Working Spin Locks with Test-And-Set

Because disabling interrupts does not work on multiple processors, and because simple approaches using loads and stores (as you saw in the previous lesson) don’t work, system designers started to invent hardware support for locking. The earliest multiprocessor systems, such as the Burroughs B5000 in the early 1960s“The Architecture of the Burroughs B5000: 20 Years Later and Still Ahead of the Times?” by A. Mayer. 1982. Available: www.ajwm.net/amayer/papers/B5000.html. “It (RDLK) is an indivisible operation which reads from and writes into a memory location.” RDLK is thus test- and-set! Dave Dahm created spin locks (“Buzz Locks”) and a two-phase lock called “Dahm Locks.”, had such support; today all systems provide this type of support, even for single CPU systems.

Test and set

The simplest bit of hardware support to understand is known as a test-and-set (or atomic exchange ...