This content originally appeared on DEV Community and was authored by Ayan Dutta
I’ve been experimenting with Java 21’s Virtual Threads (Project Loom) in my Spring Boot apps, and the way they handle concurrency is a game-changer. The key? Understanding how mounting and unmounting work under the hood.
Check out my hands-on video demo to see how it all works:
Java Virtual Threads: Deep Dive into Mounting/Unmounting & Carrier Threads Explained
https://youtu.be/IA0Hwwf9hTo
Why This Matters
Platform Threads in Java are heavy, mapping 1:1 to OS threads. Virtual Threads? They’re lightweight, letting you run thousands of concurrent tasks. The catch: they rely on carrier threads in the JVM’s ForkJoinPool.
When debugging my own apps, I noticed that knowing when a Virtual Thread mounts (gets assigned to a carrier thread) or unmounts (frees the carrier during blocking I/O) was critical to avoiding performance bottlenecks.
What You’ll Learn in the Demo
Here’s what I cover in the video:
- Platform vs. Virtual Threads → Key architectural differences.
- ForkJoinPool Scheduler → How the JVM manages carrier threads.
- *Mounting *→ How Virtual Threads are assigned to carriers.
- Unmounting → What happens during blocking I/O operations.
- CPU vs. I/O Tasks → Why they behave differently with Virtual Threads.
- JDK Internals → Insights from real code examples.
My Key Takeaway
Here’s what clicked for me: Virtual Threads unmount automatically during blocking operations, freeing up carrier threads to handle other tasks. This is why you can scale to thousands (or even millions) of concurrent tasks without killing your server’s memory.
Want to Go Further?
This video is just a taste of what I’ve been exploring with Java 21 concurrency. In my full Udemy course, I dive into:
- Advanced Virtual Thread demos in Spring Boot.
- Avoiding thread pinning pitfalls with JFR monitoring.
- Observability with Micrometer, Prometheus, and Grafana.
- Structured Concurrency and Scoped Values in real apps.
- Load testing with JMeter to prove it all works.
Want to dive deeper? **Check out my full Udemy course on **Java Virtual Threads & Structured Concurrency with Spring Boot:
https://www.udemy.com/course/java-virtual-threads-structured-concurrency-with-spring-boot/
**
Resources & Discounts**
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Email: j2eeexpert2015@gmail.com
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Browse all my discounted courses here:
https://j2eeexpert2015.github.io/learningfromexperience-courses
This content originally appeared on DEV Community and was authored by Ayan Dutta