Virtual Threads in Clojure

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2024-05-06 16:00:05

Project Loom is the codename for a project that adds virtual threads to the JVM. Virtual threads are a lightweight concurrency mechanism that allows for more concurrency than regular threads and, therefore, uses the CPUs more effectively.

The project was officially named "Virtual Threads." It was preview-released in JDK 19, with significant revisions in JDK 20 and an official release in JDK 21.

That's a great question. Concurrency means sharing the computer's limited resources (CPU, RAM, disk, network). Parallelism means adding more of a resource so more can happen simultaneously.

For example, concurrency is forming a queue to share pots of coffee at the office. Parallelism is adding more pots of coffee to share. If you have three pots of coffee, only three people can pour coffee at a time--parallelism is three. However, more people can share the coffee pots using a concurrency mechanism like a queue.

Virtual threads let us better share the computer's resources without using an asynchronous programming style. In other words, you get better performance with easier-to-understand code. Stack traces can be a problem with asynchronous code, but stack traces from virtual threads look just like those from regular threads.