Java developers spent years learning reactive programming to handle concurrency. WebFlux. Project Reactor. Non-blocking everything. Now most of that complexity might not be necessary. Virtual threads, introduced as a standard feature in Java 21 and now becoming the default in Spring Boot 4, change the equation completely. The old model: one platform thread per request. Expensive. Limited. Which is why reactive became popular. The problem with reactive: your entire codebase had to adapt. Different programming model, harder debugging, steeper learning curve, code that was harder to read and maintain. Virtual threads give you the same concurrency as reactive without changing how you write code. What that means in practice: → You write blocking-style code, readable and straightforward → The JVM handles thousands of virtual threads without the overhead → No reactive chains, no Mono, no Flux unless you actually need them → Debugging works the way you expect it to The shift happening right now: teams are setting spring.threads.virtual.enabled=true and getting WebFlux-level throughput with imperative-style code. That's not a small thing. ⚠️The mistake is ignoring this because it feels like hype. Virtual threads are not a replacement for understanding concurrency. But they do remove a lot of accidental complexity that was never the point. If you're still writing reactive code just to handle I/O concurrency, it might be worth reconsidering. Are you using virtual threads in production yet? #Java #SpringBoot #Backend #Concurrency #VirtualThreads #SoftwareEngineering #Microservices
Great post! Virtual threads are game-changers: benchmarks show 3-7x throughput gains in Spring Boot I/O APIs (e.g., 15k to 52k req/sec), p95 latency down 60%+, and 36% less memory per request vs. platform threads.
The same happens in Python. Prepending 'async' to your function name and 'await' to some expressions can bring little to none speed increase if when 'awaiting' the system is doing nothing. Yo should understand the concurrency architecture.
Great!
To be honest, virtual threads are one of the most ergonomic ways to write asynchronous code. They are inspired by BEAM processes (Erlang, Elixir) and green threads (GO) - the key advantage is that they do not have the problem of function coloring, which is typical for asynch/await+ Thread starvation is not really a think for Virtual Threads (if you are not playing with thread priorities, which honestly no one need)Although race conditions, live locks, dead locks still can occur, but it`s convenient to fix & overall it`s better to choose immutability (project Amber helps with ADT support in this case)z But there is another think - Virtual Thread pinning (meaning virtual thread is pinned into it`s carrier/platform thread so it is not able to be unbounded as always), which mostly occurs with synchronized blocks (fixed in Java 24) or JNI calls (cannot be fixed, but Java Foreign Function & Memory is a good alternative for JNI)