If you are comfortable with the latching pseudocode shown in Figures 3-6 and 3-7, you will quickly grasp Oracle's mutex algorithm shown in Figures 3-15 and 3-16. As you can see, there are some interesting twists!

Looking at Figures 3-15 and 3-16, you can quickly see some similarities between the latching and mutex algorithms. The concepts of willing to wait versus immediate (nowait), spinning, sleeping, and posting the wait event when sleeping are very similar. However, there are a few distinct differences.

It all starts with the mutex request. Just as with latches, the specific mutex is requested along with the type of either nowait (that is, immediate) or willing to wait, and the mode of either shared or exclusive. If a nowait request is made, similar to latching, a single fast get request occurs. If a willing-to-wait request occurs, a single fast get is requested; if it fails, processing drops into the familiar spin-and-sleep cycle. While both latches and mutexes have the same spin and sleep objectives, as you'll see, how this plays out in practice is very different.