Depends on what you mean by "functioning". You can make one that functions in the sense that you can lock between concurrent threads. However, it's difficult to

Depends on what you mean by "functioning". You can make one that functions in the sense that you can lock between concurrent threads. However, it's difficult to do right and even more difficult to do in a way that is performant (and the interface to the kernel is so ill defined for this, whatever efficient solution you come up with will likely prove to be far less efficient on other systems with just subtle alterations in the underlying kernel implementation.