Automated Runtime Transition between Virtual and Platform Threads in the Java Virtual Machine

Virtual threads are a new feature of the Java Virtual Machine (JVM) complementing the regular Java threads (called platform threads). Virtual threads promise a significant throughput improvement in workloads that make intensive use of blocking operations, but incur performance overheads in CPU-bound workloads, due to the cost of creating and maintaining the data structures associated with them. Hence, the optimal choice between platform and virtual threads depends on application behavior (which can change significantly during the execution) and on the system running the application. This work-in-progress paper proposes a new framework to automatically and adaptively select the type of threads created by an application, switching between platform and virtual threads as the application's behavior changes over time. The framework monitors several metrics of the running application. Based on these metrics, users can specify criteria for deciding when virtual threads should be preferred over platform threads and vice versa. We present a use case on the Eclipse Jetty web server. Our preliminary evaluation shows that the framework selects the thread type yielding the highest throughput depending on the application behavior, without introducing performance drawbacks.