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Virtual Threads in JDK 21: The End of Java’s Async Coding Nightmare?

Rasathurai Karan
Javarevisited
Published in
3 min readFeb 5, 2025

Java developers, gather around. If you’ve ever wrestled with the soul-crushing complexity of asynchronous code or hit the wall of thread limits, JDK 21 has a gift for you: virtual threads. This isn’t just another feature — it’s a game-changer that could finally let you write simple, blocking code without sacrificing performance. Let’s unpack why this matters.

Why Virtual Threads? The Problem That Broke Java’s Back

Imagine this: your code queries a database. It takes 100 milliseconds, but your CPU is idle for 99.9999% of that time. Why? Traditional platform threads (wrappers for OS threads) are expensive. Each thread costs ~2MB of memory, and creating thousands crashes your app. To scale, we resorted to async frameworks — splitting code into disjointed lambdas, drowning in CompletableFuture hell.

The result? Unreadable code, invisible stack traces, and debugging nightmares. Async worked, but the cost? Your sanity.

Virtual Threads to the Rescue: “Just Block, It’s Fine”

Virtual threads flip the script. They’re lightweight — so cheap you can launch millions without breaking a sweat. Here’s the magic:

  • 0% Blocking Overhead: When a…

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