Without it, multi-threaded applications are more error-prone when subtasks are shut down or canceled in the wrong order, and harder to understand, he said. The structured concurrency API is also designed to preserve order in multi-threaded environments by treating multiple tasks running in individual threads as a single logical unit of work. The Java virtual machine (JVM) brokers the connection between virtual threads, still assigned individually to each request, and the underlying operating system threads, optimizing CPU utilization while preserving the readability and traceability of code, Garcia-Ribeyro said. Or you can call around this one thread per request restriction and make it so that a single OS thread can handle multiple requests … for much better CPU utilization, but it comes at a terrible price - the programming model is now very unintuitive.' 'We could assign one thread to each request, will make the code easier to read … but you will be wasting resources. 'Before Loom, we had two options, neither of which was really good,' said Aurelio Garcia-Ribeyro, senior director of project management at Oracle, in a presentation at the Oracle DevLive conference this week. This was the most efficient approach when application performance was typically limited by the capacity of server CPUs, but as CPUs have become more powerful, applications are limited by I/O, according to the number of operating system threads available. Virtual threads represent a lighter-weight approach to multi-threaded applications than the traditional Java model, which uses one thread of execution per application request.

The second of these stages is commonly the last development phase before incorporation as a standard under OpenJDK. Previews are for features set to become part of the standard Java SE language, while incubation refers to separate modules such as APIs.

Project Loom features that reached their second preview and incubation stage, respectively, in Java 20 included virtual threads and structured concurrency. The features are part of a broader set of projects undertaken within the Open Java Development Kit ( OpenJDK) open source community: Project Loom, for performance and efficiency Project Amber language improvements for developer productivity Project Leyden, which seeks to reduce Java startup time, warmup time and footprint Panama, for connecting with non-Java code Valhalla, for better memory throughput and performance and the ZGC low-latency garbage collector.

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