DCEVM for Java 17 about dcevm HOT 37 OPEN

There will be.

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Not sure if it counts as it isn't directly from this project, but I noticed that the jetbrains runtime beta versions for jdk17 seem to have dcevm options available, and it seems to work for my use case (Minecraft 1.17 fabric modding).

https://github.com/JetBrains/JetBrainsRuntime/releases/tag/jbr17b135.1
has options with download links jbrsdk_dcevm-17-PLATFORM-bVERSION.tar.gz, which when using with the VM argument -XX:+AllowEnhancedClassRedefinition enables alterations to the body of a class.
I haven't run any extensive testing on it to see any limitations or differences from earlier versions of DCEVM, but it seems to work wonderfully.

Double check for a more recent release of the jbr17 betas if you follow those instructions, but otherwise hopefully this helps anyone who needs to use dcevm for java 17.

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@skybber do you have ETA ?

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We have to add it to hotswapagent pages, in the same way how the page http://hotswapagent.org/mydoc_quickstart-jdk11.html is done. Pages sources are at https://github.com/HotswapProjects/HotswapAgentPages, any help will be appreciated.

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Look at https://github.com/JetBrains/JetBrainsRuntime/releases , dcevm17 is embedded in JBR17, there isn't separate dcevm17 build. Enhanced hotswap must be explicitly turned on using -XX:+AllowEnhancedClassRedefinition

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Yes, I'm involved in the project, JB is sponsoring dcevm now.

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It is even used as a default debug enviroment for IntelliJ Idea development in Jetbrains now, it is also able to use it to run profiling tools like YourKit or JFR.

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Class hiearchy is not supported even in Jetbrains version. It has not been supported since dcevm7 and I did not port it to Jetbrains version.

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You have to use either -XX:+AllowEnhancedClassRedefinition or -XX:HotswapAgent=.. to enable advanced hotswap.

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Probably, worth noticing that the DCEVM is now integrated into the standard Jetbrains Runtime build according to JetBrains/JetBrainsRuntime#134.

Thank you!

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I need to change class hierarchy and add/remove/modify interfaces. Will check the JetBrains. Thanks

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Otherwise, interface addition/removal is supported.

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@skybber Cool, thanks!
Do you know the future of Trava OpenJDK?
Should jbr be used instead?

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Yes, jbr17 is recommended. Currently there is a bug in jbr-dcevm17, that will be fixed in the next release. Also there is an issue with HA, that is not embedded with jbr-runtime. From perspective of application developer using Spring/J2EE etc, HotswapAgent is "must have" feature.

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So, jbr with dcevm effectively cannot be used in the development process - the runtime doesn't support modifications of class signatures? Tried to add a method in an opened debug session both on jbr11 and jbr17 with dcevms with no luck:

Hot Swap failed. dcevm intellij - ...: add method not implemented dcevm intellij ...: Operation not supported by V

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Thanks, works perfectly in both 11 and 17 versions!

Regarding http://hotswapagent.org/ - for me, the solution in general even on supported JDKs (Trava) didn't work. Tried on Hibernate; the implementation relied on Hibernate internals, just stopped working with newer Hibernate releases. Thus, we can't rely on such an unstable solution in a regular development process.
For us, enhanced class redefinition would be more than enough.

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What version of Hibernate are you using? Please create issue at https://github.com/HotswapProjects/HotswapAgent, Otherwise we have tests up to v5.4.14 https://github.com/HotswapProjects/HotswapAgent/blob/master/plugin/hotswap-agent-hibernate-plugin/run-tests.sh

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@skybber, thanks for the quick response.
Unfortunately, used it quite a while ago, so can't tell the exact version.
We plan to migrate to Java17, thus we anyways will have to stick to JBR w/o HotswapAgent support.

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Not sure if it counts as it isn't directly from this project, but I noticed that the jetbrains runtime beta versions for jdk17 seem to have dcevm options available, and it seems to work for my use case (Minecraft 1.17 fabric modding).

https://github.com/JetBrains/JetBrainsRuntime/releases/tag/jbr17b135.1 has options with download links jbrsdk_dcevm-17-PLATFORM-bVERSION.tar.gz, which when using with the VM argument -XX:+AllowEnhancedClassRedefinition enables alterations to the body of a class. I haven't run any extensive testing on it to see any limitations or differences from earlier versions of DCEVM, but it seems to work wonderfully.

Double check for a more recent release of the jbr17 betas if you follow those instructions, but otherwise hopefully this helps anyone who needs to use dcevm for java 17.

Minecraft Forge modder here. Unfortunately it doesn't seem that the bootstrap launcher used by Minecraft forge is enjoying the switch to Jbr17. I believe we need these features due to our mods using Mixins and it conflicting with the ability to even hotswap inner method changes.

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Minecraft does not work with jbr17?

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Minecraft does not work with jbr17?

Turns out it was due to the Minecraft forge version, which has recently been updated!

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@skybber you are doing God's work keeping the DCEVM going. It's insane that this isn't baked into the core JVM.

Do you think there will be an "official" jdk 17 release any time soon?

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Dcevm17 is now part of jbr runtime, that is fork of JVM with a lot of enhancements. JB moved to Europe recently, I recommend to look at theirs official statement to current situation.

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Interesting. Is that good news or bad news?

When I look here:

https://github.com/JetBrains/JetBrainsRuntime

I see jdk 11 releases. Can you send me a link to their statement?

Regardless, thank you for keeping this incredibly important project alive!

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If I understand it correctly you can add HotSwapAgent manually to the JBR, so reloading will also work with spring boot and hibernate etc (TravaOpenJDK/trava-jdk-11-dcevm#46) or is this not needed?

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yes, just put HA into lib/hotswap/, and use -XX:HotswapAgent=fatjar

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That is fantastic I have it working locally. Are you still associated with the project?

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do you know when the dcevm website will be updated with this information?

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And i think the readme here should also be updated to point out the jetbrains replacement.

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Anyway, there are many dcevm fixes in JBR 11/17 now, but it's still not 100% stable, especially the rare case where adding/removing fields is difficult to solve if stack frames contain old instances replaced by scalars. Maybe Oracle is aware of this and that's why they don't include dcevm in the standard hotspot, maybe the reason is completely different - they are working on a solution in Graal, but according to the specs this solution is far from better than dcevm.

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@skybber do you have a github sponsor or similar set up? I'd like to sponsor your DCEVM work.

(Jetbrains recently sponsored me for htmx, and this is far more imporant work than that!)

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Personally I don't have it, there quite a lot of people involved in HA+dcevm, it would be ... selfish to have sponsors just for myself.

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:) Is there a place where you all meet to discuss? If so, and if you don't mind, it would be great to get this work sponsored.

This is an extremely important feature for JVM languages and I'm sure many people in the community would be willing to chip in if there were a single organization to do so through!

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pls. conntact me by an email.

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Confirmed that this works with the jbr. I got tripped up because hotswap-agent.jar is not bundled in as far as I could tell like it used to be. You'll need the hotswap agent plugin for your IDE and then add "-XX:+AllowEnhancedClassRedefinition -XX:HotswapAgent=fatjar" to your VM options. You seem to be able to ignore messages about the plugin not being able to determine the dcevm version.

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Some one from Jetbrains advised -XX:HostswapAgent is not required any more as this is baked into the JBR itself.
https://youtrack.jetbrains.com/issue/JBR-5195/I-sometime-have-my-project-that-is-blocked-from-starting-and-i-have-the-feeling-that-there-is-a-deadlock-somwhere-during-the
@skybber Can you please clarify.
Thank you!

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HotswapAgent is not in JBR, if you need it you can either:

• put hotswap-aget.jar it into $JAVA_HOME/lib/hotswap/ and use -XX:HotswapAgent=fatjar
• or use -XX:HotswapAgent=external -javaagent:<path>/hotswap-agent.jar

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