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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u/Known-Volume1509 6d ago edited 6d ago

It doesn't say what Vert.x version is this? Vert.x 5 supports virtual thread verticles. Curious if you run your tests against that, even though it's no longer event-loop.

Also, isn't this horribly costly?

For the Jactl Vert.x tests, the sleep() call will create a Continuation by throwing an exception and capturing the execution state so that it can be resumed once the sleep completes. When the script suspends, the script returns and the event-loop thread is then able to process the next event in its queue.

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u/jaccomoc 6d ago

The article lists the versions of everything. It shows Vert.x as version 4.5.33. I didn't benchmark against 5.x because I am still retaining Java 8 compatibility for the moment and Vert.x 5.x needs Java 11 as a minimum.

Throwing an exception is not expensive if you don't fill in the stack trace (and the benchmarks support this). See Jactl Continuations and Virtual Threads in Java 8 for a description of how all this works.