JVM advice: name your thread pools

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: lawrence@krubner.com

Tomasz Nurkiewicz offers this bit of advice, which sounds like it would also be useful in Clojure:

Name pool threads

I can’t emphasize this. When dumping threads of a running JVM or during debugging, default thread pool naming scheme is pool-N-thread-M, where N stands for pool sequence number (every time you create a new thread pool, global N counter is incremented) and M is a thread sequence number within a pool. For example pool-2-thread-3 means third thread in second pool created in the JVM lifecycle. See: Executors.defaultThreadFactory(). Not very descriptive. JDK makes it slightly complex to properly name threads because naming strategy is hidden inside ThreadFactory. Luckily Guava has a helper class for that:

import com.google.common.util.concurrent.ThreadFactoryBuilder;

final ThreadFactory threadFactory = new ThreadFactoryBuilder()
.setNameFormat(“Orders-%d”)
.setDaemon(true)
.build();

final ExecutorService executorService = Executors.newFixedThreadPool(10, threadFactory);
By default thread pools create non-daemon threads, decide whether this suits you or not.

Switch names according to context

This is a trick I learnt from Supercharged jstack: How to Debug Your Servers at 100mph. Once we remember about thread names, we can actually change them at runtime whenever we want! It makes sense because thread dumps show classes and method names, not parameters and local variables. By adjusting thread name to keep some essential transaction identifier we can easily track which message/record/query/etc. is slow or caused deadlock. Example:

private void process(String messageId) {
executorService.submit(() -> {
final Thread currentThread = Thread.currentThread();
final String oldName = currentThread.getName();
currentThread.setName(“Processing-” + messageId);
try {
//real logic here…
} finally {
currentThread.setName(oldName);
}
});
}

Inside try-finally block current thread is named Processing-WHATEVER-MESSAGE-ID-IS. This might come in handy when tracking down message flow through the system.

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