I believe those threads are tied to an event group loop, essentially acting as a thread pool over time. Perhaps follow to/from https://github.com/apache/activemq-artemis/blob/2.42.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/remoting/impl/netty/NettyConnector.java#L531-L534
(note: if looking on main, or the 2.43.0 candidate under vote, the name of the threads changed since 2.42.0) On Tue, 14 Oct 2025 at 10:13, Thorsten Meinl <[email protected]> wrote: > > Attached is a reproducer for the behaviour. Run with > > mvn compile exec:java > > and monitor the output with the active threads. It's constantly > increasing to 56 (in my case) and then stays constant. Therefore I > don't think it's an actual issue since the number of threads seems to > be bounded after all but I find the behaviour strange nevertheless. > > After some debugging I also believe that these threads ("ActiveMQ- > client-netty-threads") are _not_ part of a thread pool but somehow tied > to the JMS context and not cleaned up right after the context is > closed. > > For us this means we just need to provide a bit more of direct memory, > 20MB seems to be sufficient. > > Cheers, > > Thorsten > > > Am Montag, dem 13.10.2025 um 12:04 -0500 schrieb Justin Bertram: > > It's hard to comment without more details. Is this the same client as > > before that's using 2.42.0? What connection URL are you using? Do you > > have > > a reproducer you could share? Is this a regression or a new issue? > > > > This documentation [1] might be of some help. > > > > Out of curiosity, what is the purpose of the management message? I'm > > always > > trying to understand better how folks use our software, especially > > the > > management API, so we can add new features or improve existing ones. > > > > > > Justin > > > > [1] > > https://activemq.apache.org/components/artemis/documentation/latest/thread-pooling.html#client-side-thread-management > > > > On Mon, Oct 13, 2025 at 11:15 AM Thorsten Meinl > > <[email protected]> > > wrote: > > > > > Good evening, > > > > > > I am tracking down (yet another) memory issue on one of our Artemis > > > client applications. We set very low limits for direct memory that > > > Java > > > is allowed to use, 13MB in this particular case. After starting the > > > application, the "direct buffers" in use increase up to when no > > > more > > > direct memory can be allocated. The application does not do > > > anything > > > than listen on a topic and send and consume a management message > > > every > > > 30 seconds. It does _not_ consume or send any other messages. Yet, > > > I > > > see 47 "ActiveMQ-client-netty-threads" threads existing. All of > > > them > > > are idle in "io.netty.channel.epoll.Native.epollWait". If all of > > > these > > > threads use some thread-local netty buffer it would explain the > > > constant growth. Which brings me to the main question: why would > > > one > > > see 47 such threads if there is almost nothing going on in the > > > application? I would assume that a handful of threads should be > > > sufficient since they can easily get re-used. > > > > > > Cheers, > > > > > > Thorsten > > > > > > -- > > > Dr.-Ing. Thorsten Meinl > > > KNIME AG > > > Talacker 50 > > > 8001 Zurich, Switzerland > > > > > > > > > ------------------------------------------------------------------- > > > -- > > > To unsubscribe, e-mail: [email protected] > > > For additional commands, e-mail: [email protected] > > > For further information, visit: https://activemq.apache.org/contact > > > > > > > > > > > -- > Dr.-Ing. Thorsten Meinl > KNIME AG > Talacker 50 > 8001 Zurich, Switzerland > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [email protected] > For additional commands, e-mail: [email protected] > For further information, visit: https://activemq.apache.org/contact --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected] For further information, visit: https://activemq.apache.org/contact
