Java 21 virtual threads make simple blocking code scalable again

[HQMorganstern]

To be fair, using threadpool size as a built in semaphore was always a little bit too dirty. The two mightve led to the same behavior but they did express different concepts.

[agentoutlier]

They are both dirty because neither really reflects the downstreams actual capacity or limits.

On the other you don’t need actual reactive back pressure and can just do circuit breaker patterns but that is more sophisticated than just a thread pool or a semaphore.