On Analyzing Virtual Threads – a Structured Concurrency Model for Scalable Applications on the JVM

Various blocking operations, such as input/output (IO) operations, are an essential functionality of concurrent applications. However, these operations often cause efficiency-related challenges in multithreaded applications because of the single-thread access policy. IO operations' speed and efficiency heavily rely on operating system (OS) threads and scheduling processes, which is time consuming because of the insufficient distribution of OS resources. Because of their overgeneralization, required to support various usage scenarios, robust OS kernel threads are commonly heavyweight and oversized, created in a limited number, and heavily dependent on OS schedulers. Various asynchronous programming techniques tackled issues in implementing modern concurrent applications with blocking operations with the complete reconstruction of threads and their schedulers. Based on our previous preliminary research, we further explored a model of structured concurrency in Java Virtual Machine (JVM), through the updated implementation of virtual threads and accompanying schedulers, as a novel form of lightweight user-mode threads in the JVM, decoupled from OS threads and managed within the JVM. In this paper, we present our findings about the efficiency of those schedulers utilized for virtual threads on blocking operations, compared with the implementation of OS threads' schedulers, and review possibilities of reducing memory footprints and context switching costs.