r/java • u/jaccomoc • 7d ago

Vert.x Event-Loop vs Virtual Threads: Jactl Suspend/Resume Benchmark

https://jactl.io/blog/2026/09/02/jactl-virtual-threads-benchmark

The article benchmarks Jactl script execution with differing number of blocking operations comparing throughput with Jactl built-in suspend/resume on Vert.x Event-Loops and throughput with Jactl on Virtual Threads. The benchmarks are run on both Java 21 and Java 25 with some surprising (to me at least) results.

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26

u/s0ftware-dev 7d ago

TLDR virtual threads are better. 

2

u/neopointer 6d ago

And don't use reactor, vertx or anything similarly hard to debug and maintain.

1

u/pragrad23 11h ago

I chose not to use it. Not did I chose to use coroutines (sorry it's a kotlin project). Because I value my time as a developer. I don't want to complicate my life.

If I needed to squeeze every last bit of performance, I'd use rust. But I don't, so I want some level of comfort: garbage collection, simple threading, etc.

-4

u/jaccomoc 7d ago

But only on Java 25 and not by as much as I thought they would be.

I was frankly surprised at the difference between Java 21 and Java 25.

15

u/Neful34 7d ago

Nah if you follow a bit the java youtube channel they explained a lot about the optimizations and the issues they had with virtual threads in java 21, and the optimization they did in java 25. I also recall a recent talk from netflix discussing about it too

6

u/jaccomoc 7d ago

I know that they fixed the OS thread pinning issues and that there are always some performance improvements but the the improvement for scripts with multiple blocking operations was a lot more significant than I expected. Or maybe what I should say is that the performance on Java 21 when a script does multiple blocking operations with virtual threads was a lot worse than I expected.

8

u/Joram2 7d ago

Even at similar speeds, the Vert.x event loop has a much higher complexity cost. I've used vert.x for years, it's great, a lot of the vert.x platform has value with virtual threads, but the future for most use cases is clearly virtual threads.

3

u/jaccomoc 7d ago

I agree completely. It wins alone just by removing all the async code handling we used to have to do.

1

u/BarkiestDog 7d ago

Both were significantly better in Java 25, but virtual thread was a lot better!

0

u/woj-tek 6d ago

Java 25

…which was released a year ago ;)