Java Performance: The Definitive Guide

Chapter 9. Threading and Synchronization Performance

From its first days, some of Java’s appeal has been because it is multithreaded. Even in the days before multicore and multi-CPU systems were the norm, the ability to easily write threaded programs in Java has been considered one of its hallmark features.

In performance terms, the appeal is obvious: if two CPUs are available, then an application might be able to do twice as much work, or the same amount of work twice as fast. This assumes that the task can be broken into discrete segments, since Java is not an autoparallelizing language that will figure out the algorithmic parts. Fortunately, computing today is often about discrete tasks: a server handling simultaneous requests from discrete clients, a batch job performing the same operation on a series of data, mathematical algorithms that break into constituent parts, and so on.

This chapter explores how to get the maximum performance out of Java threading and synchronization facilities.

Thread Pools and ThreadPoolExecutors

Threads can be managed by custom code in Java, or applications can utilize a thread pool. Java EE application servers are built around the notion of one or more thread pools to handle requests: each servlet call into the server is handled by a (potentially different) thread from the pool. Similarly, other applications can use Java’s ThreadPoolExecutor to execute tasks in parallel.

In fact, some Java EE application servers use instances of the ThreadPoolExecutor ...