6 · Advanced · lesson 37 of 41

Virtual Threads (Project Loom)

Millions of cheap threads scheduled on a few carriers (Java 21+).

Java

try (var exec = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 1_000_000; i++) {
        exec.submit(() -> {
            Thread.sleep(Duration.ofSeconds(1));
            return null;
        });
    }
}

NOTE

Virtual threads are managed by the JVM, not the OS. Blocking is nearly free.

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Key takeaways

✓Write blocking code; the JVM parks/unparks the virtual thread.
✓Great fit for I/O-heavy servers.

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