AbstractJava is becoming a viable platform for real‐time computing. There are production and research real‐time Java VMs, as well as applications in both the military and civil sectors. Technological advances and increased adoption of real‐time Java contrast significantly with the lack of benchmarks. Existing benchmarks are either synthetic micro‐benchmarks, or proprietary, making it difficult to independently verify and repeat reported results. This paper presents the CDx benchmark, a family of open‐source implementations of the same application that target different real‐time virtual machines. CDx is, at its core, a real‐time benchmark with a single periodic task, which implements an idealized aircraft collision detection algorithm. The benchmark can be configured to use different sets of real‐time features and comes with a number of workloads. It can be run on standard Java virtual machines, on real‐time and Safety Critical Java virtual machine, and a C version is provided to compare with native performance. Copyright © 2010 John Wiley & Sons, Ltd.