What does Sleepless Window thread actually do and how is it implemented?

[Aetopia]

Reference:

SpecialK/src/scheduler.cpp

Line 1026 in 2575f70

const bool sleepless_window = config.render.framerate.sleepless_window;

As the name of the option, suggests it makes the Window Thread sleepless but in what sense? Additionally how is it implemented?

[Aemony]

Same way the CPU core spoofing was implemented — it detours some standard Win32 API calls and implements custom code/checks that manipulates the input (that being the game’s originally coded sleep duration) and executes Special K’s custom duration instead.

Any game that implements sleeping using the detoured API calls will end up running SK’s code instead, which allows us to skip the sleep call entirely or adjust it to our own liking.

[Kaldaien]

It replaces Sleep (...) calls on window threads with a wait function (MsgWaitForMultipleObjects (...)) that will wake up when there's a waiting message on the queue.