Virtual threads

Lightweight threads from Project Loom, and when they replace a thread pool.

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

Explain how a virtual thread differs from a platform thread
Run blocking I/O on virtual threads and explain why a pool is unnecessary
Spot the synchronized block that pins the carrier thread

In practice

A few lines that show Virtual threads doing its job.

Java

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    List<Future<String>> pages = urls.stream()
        .map(url -> executor.submit(() -> fetch(url)))   // blocking is fine here
        .toList();
    for (var page : pages) System.out.println(page.get().length());
}

// Spring Boot: spring.threads.virtual.enabled=true

The common mistake

Watch for

Pooling virtual threads or holding a synchronized block around blocking I/O. Both pin the virtual thread to its carrier and lose the benefit; create them freely and prefer ReentrantLock around blocking calls.

What to know first

Your roadmap puts these before Virtual threads, unless you already know them.

Threads and thread safety

How it stays learned

Once a session shows you understand Virtual threads, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

Day 3First recall, while it is fresh
Day 7Second, a week on
Day 18Last, when it has settled

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