Haiku's (Kernel) Condition Variables API: Design & Implementation
A few months after my contract with Haiku, Inc. began, I rewrote the implementation of the Haiku kernel’s condition variables (as opposed to our userspace condition variables, which are from POSIX.) As this new implementation has run in Haiku for over a year and shipped in the latest release with no sign of any remaining issues, I figured it is high time for a deep-dive on the API, its implementation history, and the design of the new implementation I wrote.
I expect this article will be of broader interest than just to Haiku’s community, because Haiku’s condition variables API has some notable (and powerful) features not found in those of other operating systems, and its implementation is thus likewise unique (at least, as far as I have been able to figure out.)