v4. The fastest implementation that is theoretically possible and can be implemented on major platforms. Almost twice as fast as pthread mutex.
**TODO: Recursive Mutex.**
```text Time elapsed: t1=3.191000ms, t2=5.786000ms ```
Thanks to the article `Futexes Are Tricky` by `Ulrich Drepper` from `Red Hat, Inc.`
https://dept-info.labri.fr/~denis/Enseignement/2008-IR/Articles/01-futex.pdf