An Exploration of Java's JIT

Series Overview

HotSpot has been the defacto JVM for over 20 years and shows no signs of being replaced, despite Graal's growing popularity. HotSpot has been the stage for a number of impressive technological innovations in both the Garbage Collector and JIT spaces, with many insiders having published good technical deep-dives on many of these internals.

Java has been able to deliver impressive performance within the constraints of the language, with its optimising C2 compiler utilising runtime application profiles to deliver PGO for over 20 years on billions of devices. Despite this, a fairly wide gap remains between the performance of an application written in Java and one written in C++, even in domains where the overheads imposed by Java shouldn't be a major factor.

This series seeks to provide an outside look at the C2 JIT and try to explore some of the headroom available for Java to get even faster. Java will never match C/C++ compilers overall, but I hope to show that it can get a lot closer to native code than it presently is.

A new entry will be posted roughly twice a month until the series is complete.

Series Entries