Continuations: The magic behind virtual threads in Java
summary
Explains how Java 21 virtual threads use continuations to pause and resume execution, showing the actual API calls Continuation.doYield/doRun and constructing continuations with new Continuation(scope, runnable); builds a toy scheduler using ExecutorService and ScopedValues, simulates blocking with a Timer, and implements a simple VirtualThread class. Demonstrates performance: 2,000 virtual threads on 10 platform threads finish quickly while a plain platform-thread version runs far longer. Notes continuations remain internal to the JDK for now.
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chapters (10)
- 0:00Introduction to talk
- 1:51Virtual threads overview
- 5:03Creating virtual threads
- 8:04Understanding continuations
- 10:14Continuation API demo
- 15:29Stack management mechanics
- 18:02Generators with continuations
- 19:40Implementing the generator
- 25:42Building virtual threads
- 44:22Summary and Q&A
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