Java 21: The revolution of virtual threads - A Deep dive
summary
Shows migrating a Spring Boot app from blocking to reactive to Java 21 virtual threads, using JMeter with 1,000 concurrent users and artificial delays (1,000ms and 500ms). Demonstrates an OOM when creating 1 million platform threads and then running the same load with virtual threads served by ~40 OS worker threads, cutting the blocking endpoint to ~1s and the speaker+talks flow to ~1.5s using structured task scope and a small CollectionTaskScope helper. Notes risks: thread‑local leaks, synchronized/ native calls, and CPU‑bound work.
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chapters (13)
- 0:00Java 21 and virtual threads
- 1:50Blocking Spring Boot app
- 6:25Platform threads vs blocking I/O
- 11:41Reactive with CompletableFuture
- 15:13Reactive code complexity
- 22:57Project Loom and virtual threads
- 24:04How virtual threads work
- 26:34Creating and testing virtual threads
- 30:17Migrating Spring Boot to virtual threads
- 33:07Structured concurrency with virtual threads
- 37:25Custom scopes for concurrency
- 40:58ThreadLocals pitfalls
- 43:28Conclusion and future
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