Too busy to write a decent post so instead I'll put up a link to a paper we did a couple of years ago but wasn't yet accepted (we've been busy with other stuff).
It's 10 (yes, ten!) new algorithm to do mutual exclusion for the two-thread problem.
They're alternatives to Dekker's or Peterson's protocols. If you don't know what those are then take a look at wikipedia:
All of our 10 algorithms (did I say we had 10 of them?) have a minimum number of stores of 1 to acquire and another store to release the lock. This is something new in the world of 2-thread mutual exclusion: