Adaptive Thread Type Selection on the Java Virtual Machine

Virtual threads are a novel addition to the Java Virtual Machine (JVM). With respect to regular Java threads (called platform threads), virtual threads exhibit a substantial enhancement in throughput for tasks involving extensive use of blocking operations, but impose performance overheads on CPU-bound tasks due to the costs of managing the related data structures. Consequently, the best thread type (i.e., virtual or platform) greatly depends on the application behavior (which can change at runtime) and on the system running the application.This position paper introduces the design of a new framework which adaptively determines the thread type created by an application as its behavior changes over time. Users can define criteria specifying under which conditions one or the other thread type is preferred. These criteria are based on several dynamic metrics, which are tracked by our framework. We show that a preliminary implementation of the framework is effective in adapting to the best performing thread type as the application executes, without introducing noticeable performance penalties.