virtual-threads.yaml

---
id: 46
slug: "virtual-threads"
title: "Virtual threads"
category: "concurrency"
difficulty: "beginner"
jdkVersion: "21"
oldLabel: "Java 8"
modernLabel: "Java 21+"
oldApproach: "Platform Threads"
modernApproach: "Virtual Threads"
oldCode: |-
  Thread thread = new Thread(() -> {
      System.out.println("hello");
  });
  thread.start();
  thread.join();
modernCode: |-
  Thread.startVirtualThread(() -> {
      IO.println("hello");
  }).join();
summary: "Create millions of lightweight virtual threads instead of heavy OS threads."
explanation: "Virtual threads are lightweight threads managed by the JVM, not the\
  \ OS. You can create millions of them without tuning thread pools. They're ideal\
  \ for I/O-bound tasks like HTTP calls and database queries."
whyModernWins:
- icon: "⚡"
  title: "Lightweight"
  desc: "Virtual threads use KB of memory, platform threads use MB."
- icon: "♾️"
  title: "Scalable"
  desc: "Create millions of threads — no pool sizing needed."
- icon: "🧹"
  title: "Simple model"
  desc: "Write blocking code that scales like async code."
support:
  state: "available"
  description: "Widely available since JDK 21 LTS (Sept 2023)"
prev: "streams/optional-or"
next: "concurrency/structured-concurrency"
related:
- "concurrency/thread-sleep-duration"
- "concurrency/scoped-values"
- "concurrency/completablefuture-chaining"
docs:
- title: "Virtual Threads (JEP 444)"
  href: "https://openjdk.org/jeps/444"
- title: "Thread.ofVirtual()"
  href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Thread.html#ofVirtual()"