Significant degradation of Thread.sleep with virtual threads in JDK 25 vs JDK 21

[Fredriksson, Christian]

Thank you.
Unfortunately I've been unable to reproduce it locally outside of our runtime environment, but I do have a reliable reproducer there.

Would it help if I test this also with JDK 24/23/22?

Otherwise I can wait until JDK-8370887 is fixed (next release of JDK 25?) and test again then.

Regards,
Christian




________________________________
From: Alan Bateman <alan.bateman at oracle.com>
Sent: Friday, November 21, 2025 6:37:52 PM
To: Fredriksson, Christian <christian.fredriksson.2 at volvocars.com>; loom-dev at openjdk.org <loom-dev at openjdk.org>
Subject: Re: Significant degradation of Thread.sleep with virtual threads in JDK 25 vs JDK 21

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On 21/11/2025 15:52, Fredriksson, Christian wrote:

Hey,



I believe I have found a bug with JDK 25 and virtual threads, but will need some guidance in what information I need to provide in order to file a bug.



Short version: after changing from JDK 21 to JDK 25, doing Thread.sleep(1) in a virtual thread now sometimes takes up to 60 seconds (!).



Thanks for the mail. Do you have a standalone test that uses the loop in your mail that we could use to study this?  The timer support has changed significantly twice between JDK 21 and JDK 25. From your mail then it could be a pathological case that leads to starvation, or it could be related to recently reported bug [1].

-Alan

[1] https://bugs.openjdk.org/browse/JDK-8370887
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