Always Name Your Thread Pools

Our software tends to use a lot of thread pools – mostly through java.util.concurrent.ExecutorService implementations (Created via Executors.new.... We create these for various async use-cases, and they can be seen all over the place. All of these executors have a thread factory. It’s hidden in the default factory method, but you can supply a thread factory. If not supplied, a default thread factory is used whenever a thread is needed.

When using Spring, those can be created using <task:executor />. In that case, each executor service’s thread factory is provided by Spring and it uses the name of the executor bean (specified with id="executorName"). But for those not created by Spring, a default name is used, which isn’t helpful and doesn’t let you differentiate threads by name.

And you need to differentiate threads by name – in case of performance issues you have various options to investigate: thread dumps and using the top command. In both cases, it’s useful to know what function does a thread service, as the stacktrace in the dump might not always be revealing.

And my favorite tool for quick investigation is top. More precisely, top -H -p <pid>. This shows the usual top table, but the -H flag means that threads for the chosen process should be printed. You basically get the most CPU-heavy and currently active threads, by name. In those cases, it’s extremely useful to have custom names.

But how do you set a name? By specifying a named thread factory when creating each executor. Here’s a StackOverflow answer with multiple ways to achieve thread naming.

The method that I’m using is based on the 2nd answer:

x

public class AsyncUtils {

    public static ThreadFactory createNamedThreadFactory(String name) {

        return new ThreadFactoryBuilder().setNameFormat(name + "-%d").build();

    }

}

Centrally managing all executors through Spring might be a better idea, but not everyone is using Spring and sometimes an executor is needed for a small piece of functionality that could even go outside Spring Beans. So it’s a good idea to have that method up your sleeve.