Add Jetty options for acceptor/selector threads #534

k13gomez · 2025-08-27T18:27:03Z

Java's virtual threads (Project Loom) provide concurrency improvements with lower memory overhead compared to platform threads. This is particularly beneficial for I/O-heavy applications where thousands of concurrent connections are common.

Different workloads benefit from different acceptor/selector thread configurations. High-throughput scenarios may need more acceptors, while I/O-intensive workloads benefit from tuned selector counts.

This PR makes it very easy to ~~use VirtualThreadPool as well as~~ tune the acceptor/selector threads, otherwise the user has to rely in configuring the server via configurator and re-create the ServerConnector from scratch with custom selector/acceptor values.

Changes included:
~~- Virtual Thread Pool Support: New :virtual-pool? option creates a VirtualThreadPool instead of QueuedThreadPool (requires Java 19+)~~

Connector Thread Configuration: Added :acceptor-threads and :selector-threads options for fine-tuning connection handling, very important when using VirtualThreadPool.
- VirtualThreadPool Defaults: Virtual thread pools benefit from fewer acceptor threads (1) since virtual threads have lower overhead. Default selector count matches available processors for optimal I/O handling if not specified.
- CI Test Matrix: Extended test matrix to cover Java 17, 19, 21, and 24 with proper preview feature handling, since VirtualThreadPool is supported in Java 19 (preview), or Java >= 21, but not on Java 17.

k13gomez · 2025-08-27T22:40:15Z

@weavejester for when you have a chance to review/consider this MR, I think because I changed the Github workflow it did not run automatically, but it passed here: https://github.com/k13gomez/ring/actions/runs/17280405265 so all the tests should be passing.

weavejester · 2025-08-28T01:03:00Z

Thanks for the PR. I'll try to review it soon. Could you explain why not use Jetty's default values for the acceptors and selectors when using virtual thread pools? I'm guessing Jetty doesn't take into account the pool being used?

weavejester · 2025-08-28T01:15:50Z

Having taken a look through it, I think we probably need to break this PR into two: one that adds options to configure acceptor/selector thread counts, and one that adds a virtual pool. The acceptor/selector PR should be fairly straightforward, but I'm not yet convinced a :virtual-pool? option is the right way to go for virtual thread support.

If the acceptor/selector values are -1, then Jetty will use its defaults. This should cut down on some of the code.

k13gomez · 2025-08-28T01:57:57Z

Sounds good, I will remove the virtual pool changes for now, which are less important, and focus on acceptor/selector portion of it. The acceptor/selector options can severely affect how Jetty 12 behaves under a purely async system using virtual thread pools (which can be passed via :thread-pool), so it will help to be able to set them without having to rebuild the connector via a custom configurator.

I will put together an example project with some load testing, this is something we recently experienced in our prod environment when moving from Ring 1.13.0 to 1.14.2, but should be able to duplicate it in isolation.

weavejester

Some minor changes/questions, but overall looks good.

weavejester · 2025-08-28T01:04:45Z

ring-jetty-adapter/src/ring/adapter/jetty.clj

  :keystore-scan-interval - if not nil, the interval in seconds to scan for an
                            updated keystore
  :thread-pool            - custom thread pool instance for Jetty to use
+  :virtual-pool?          - use a VirtualThreadPool (requires Java 19+)


:virtual-threads? is a better name for the option I think:

:virtual-pool? - use virtual threads (requires Java 19+)

yeah, I like it better, will open a separate PR for that.

Sorry, I wasn't expecting that comment to get through to this review. That was from my previous (incomplete and pending) review.

weavejester · 2025-08-28T01:06:56Z

ring-jetty-adapter/src/ring/adapter/jetty.clj

+(defn- create-virtual-threadpool [options]
+  (let [max-threads         (options :max-threads 50)
+        pool                (VirtualThreadPool. max-threads)]
+    pool))


Could be more concisely written as:

(defn- create-virtual-threadpool [options] (VirtualThreadPool. (:max-threads options 50)))

I'll keep this in mind for a separate PR

Oops! That was from my previous (incomplete) review. I wasn't expecting it to still have those comments after you updated the code.

weavejester · 2025-08-28T13:30:10Z

ring-jetty-adapter/src/ring/adapter/jetty.clj

+  (let [acceptors (options :acceptor-threads -1)
+        selectors (options :selector-threads -1)]
+    (ServerConnector. server (int acceptors) (int selectors)
+                      ^{:tag "[Lorg.eclipse.jetty.server.ConnectionFactory;"}


Why ^{:tag "..."} and not ^"..."?

weavejester · 2025-08-28T13:33:20Z

ring-jetty-adapter/src/ring/adapter/jetty.clj

+  :acceptor-threads       - the number of acceptor threads to use (default -1, i.e. defer to Jetty)
+  :selector-threads       - the number of selector threads to use (default -1, i.e. defer to Jetty)


Lines go over 80 characters. Probably better to have:

:acceptor-threads - the number of acceptor threads to use :selector-threads - the number of selector threads to use

If these options aren't set, I think a sensible default is implied.

weavejester · 2025-08-28T13:34:43Z

.github/workflows/test.yml

+    strategy:
+      matrix:
+        java_version: [17, 19, 21, 24]


Changes to test.yml aren't necessary for the acceptor/selector options, right?

correct, I'll remove these for now

k13gomez · 2025-08-28T13:56:16Z

The scope of the PR is now reduced to just adding the acceptor/selector threads configuration capability, maintaining prior behavior but making these values now more easily configurable.

weavejester · 2025-08-28T14:08:18Z

Thanks! Finally, can you change the commit message to:

Add Jetty options for acceptor/selector threads

This puts the commit message subject under 50 characters. Once that's done, I'll merge and cut a new 1.15 beta release.

Regarding the :virtual-pool? or :virtual-threads? option, I'm unsure if I like an option that changes other defaults, so I'll need to give that some consideration. I'm currently on the fence about it. Hopefully that shouldn't impact people too much, though, as they can add the VirtualThreadPool via the :thread-pool option.

k13gomez · 2025-08-28T15:21:46Z

I just changed the commit message.

Regarding the virtual-threads? option, I think it can wait too, I'll think on it some more and open separate PR for that and we can explore it, but generally it will be much simpler than the initial approach without changing default acceptors/selectors or changing anything really other than it would just switch the QueuedThreadPool for a VirtualThreadPool :max-threads if specified, so all the other logic that changes default acceptors/selectors would not be there.

weavejester · 2025-08-29T22:59:32Z

Merged. I'll cut a new beta release soon. Thanks for the PR!

k13gomez force-pushed the add-loom-and-connector-config branch from e303a27 to e2fa56e Compare August 27, 2025 22:35

k13gomez force-pushed the add-loom-and-connector-config branch from e2fa56e to 276431e Compare August 28, 2025 04:23

k13gomez changed the title ~~Add support for virtual-pool and connector threads configuration~~ Add support for acceptor and selector threads configuration Aug 28, 2025

weavejester requested changes Aug 28, 2025

View reviewed changes

k13gomez force-pushed the add-loom-and-connector-config branch from 276431e to bc58578 Compare August 28, 2025 13:53

Add Jetty options for acceptor/selector threads

7e63583

k13gomez force-pushed the add-loom-and-connector-config branch from bc58578 to 7e63583 Compare August 28, 2025 15:17

k13gomez changed the title ~~Add support for acceptor and selector threads configuration~~ Add Jetty options for acceptor/selector threads Aug 28, 2025

k13gomez requested a review from weavejester August 28, 2025 17:07

weavejester merged commit a3a25ff into ring-clojure:master Aug 29, 2025
1 check passed

		:acceptor-threads - the number of acceptor threads to use (default -1, i.e. defer to Jetty)
		:selector-threads - the number of selector threads to use (default -1, i.e. defer to Jetty)

Add Jetty options for acceptor/selector threads #534

Add Jetty options for acceptor/selector threads #534

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k13gomez commented Aug 28, 2025

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k13gomez commented Aug 27, 2025 •

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