Java Virtual Threads Deep Dive: How Mounting & Unmounting Really Work

Java 21 introduced Virtual Threads (Project Loom) — lightweight threads that make massive concurrency possible.

But the real magic is under the hood: mounting and unmounting.

In this video, I’ll explain how Virtual Threads are scheduled, how carrier threads work, and why this matters for Spring Boot developers.

🔍 Why This Matters

• Platform Threads = 1:1 with OS threads → heavy, limited.
• Virtual Threads = lightweight and plentiful.
• But they still run on carrier threads in the JVM’s ForkJoinPool.

Knowing when a Virtual Thread mounts (assigned to a carrier) and unmounts (frees carrier during blocking I/O) is critical to avoid performance bottlenecks.

📚 What You’ll Learn

• Platform vs Virtual Threads → Key architectural differences
• ForkJoinPool Scheduler → How the JVM manages carrier threads
• Mounting → How Virtual Threads get assigned
• Unmounting → What happens during blocking I/O
• CPU vs I/O tasks → Why they behave differently
• JDK internals → Insights from real code examples

💡 Key Takeaway

Virtual Threads automatically unmount during blocking operations, freeing carrier threads to handle other work.

That’s why Java apps can scale to thousands (or even millions) of concurrent tasks without killing memory.

📚 Want to Go Further?

This video is just the start. In my Udemy course, I dive deeper into:

• Advanced Virtual Thread demos with Spring Boot
• Debugging thread pinning with JFR monitoring
• Observability with Micrometer, Prometheus, Grafana
• Structured Concurrency & Scoped Values in real apps
• Performance testing with JMeter

👉 Java Virtual Threads & Structured Concurrency with Spring Boot

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