Thread Priority

Every Java thread carries a number between 1 and 10 called its priority. That number is a hint to the scheduler: a higher priority means "please run this one a bit more often if you can." The word hint matters. The JVM doesn't promise anything about who runs first, when, or for how long. This lesson covers the priority API (setPriority, getPriority, the three named constants), how the JVM maps Java priorities onto the operating system's scheduler, where priority can be useful, where it fails badly, and why you should never confuse it with a synchronization tool.

This is one of the smaller chapters in the multithreading section, on purpose. Priority looks like a powerful lever at first glance, and it's not. Once you understand how thin the guarantees are, leaving priorities at the default becomes the obvious choice.