Fantastic Virtual Threads and How to Monitor Them
summary
Project Loom arrives in Java 21 with lightweight virtual threads and the demo shows monitoring via JFR adds four events, jcmd thread dump JSON and UI tools JMC/VisualVM. A Spring Boot app creates many virtual threads (recording shows 68 virtual threads), JFR flags five thread pin events each ~5s tied to a synchronized block plus a random Thread.sleep, and switching the synchronized block to a ReentrantLock and removing the sleep eliminates the errors.
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chapters (11)
- 0:00Introduction and demo setup
- 3:31What are virtual threads
- 13:40Virtual thread spinning explained
- 15:48Monitoring tools overview
- 16:53Using jcmd for diagnostics
- 26:18JDK Flight Recorder deep dive
- 32:00JDK Mission Control walkthrough
- 35:13VisualVM overview
- 37:46Monitoring virtual threads in action
- 44:34Fixing the demo application
- 45:17Q&A on virtual thread pinning
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