Protect a scarce resource with a Semaphore
Virtual threads (Java 21, JEP 444) are threads managed by the JVM instead of the operating system. They're so cheap that you can start one per task, even a million of them, and write simple blocking code that scales like asynchronous code.
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Practice questions
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Write a program that starts 1,000 virtual threads with Thread.ofVirtual(), each adding 1 to an AtomicInteger, joins them all and prints the total.
Explain it without notes
What is a virtual thread and how is it different from a platform thread?
Why don't virtual threads speed up CPU-bound work?
How should you limit concurrency when using virtual threads?
Expected output
200 queries done; at most 5 connections at once: true