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Issues with MAT reading AdoptJDK openj9 core.dmp files [message #1843278]

Thu, 22 July 2021 09:12

Eclipse User

Good morning,

I'm testing capturing various dump files in AdoptJDK openj9. I found a peculiar issue and no answers online.

Basically, generate a SYSTDUMP or core.dmp file via jcmd or Xdump. The JVM's running AdoptJDK openj9 11.0.10.9 flavors. I'm currently running Eclipse MAT versions 1.11 or 1.12 with the latest IBM DTFJ plugin.

Next, open the core.dmp file using MAT 1.11 or 1.12 and during index creation MAT generates a .threads file. The .threads file's missing thread stack traces and locals, Note, an openj9 javacore file created at the same time shows both Java and Native callstacks. I've attached a thread's stack found in a javacore file plus the .threads file. The current Java version's Eclipse OpenJ9 VM AdoptOpenJDK (build openj9-0.24.0, JRE 11 Windows 10 amd64-64-Bit Compressed References 20210120_899 (JIT enabled, AOT enabled).

I've reviewed core.dmp's running a Java class to simple deadlocks or core.dmp files created from a running Tomee instance. Also, tested the simple deadlock's class on AdoptJDK Hotspot version and MAT successfully shows thread stack traces. The AdoptJDK Hotspot generated .threads file contains both stack traces and locals addresses.

The attached zip file contains:
• A MAT created .threads file
• Openj9 javacore thread stack trace example
• A MAT Partial Threads Tab.jpg showing a few threads and no greater than (>) symbol to expand the threads
• A Eclipse MAT installed plugin versions.jpg showing installed MAT 1.12 plugin versions

The issue, how do you analyze an AdoptJDK openj9 core.dmp file's to find the Thread retaining excessive heap memory without looking at the stack trace and locals in MAT? The referenced objects help identify problematic code. Also, the data's necessary because no javacore files exist.

Any suggestions? Questions, please let me know.

Thanks,
Rich

Attachment: ExampleMissing Thread_StackTraces_Locals.zip
(Size: 441.26KB, Downloaded 115 times)

Re: Issues with MAT reading AdoptJDK openj9 core.dmp files [message #1843284 is a reply to message #1843278]

Thu, 22 July 2021 10:41

Eclipse User

I think this is a known problem - see bug 567819 and bug 558984

The Eclipse MAT DTFJ parser uses an IBM DTFJ OSGi plugin which works with dumps from IBM VMs. The OpenJ9 dumps have slightly different VM structures and the IBM DTFJ OSGi plugin can't properly read those. The matching OpenJ9 DTFJ classes can read those dumps, but those DTFJ classes are part of the VM and are not easily extractable to make an Eclipse OSGi plugin for use with MAT.

Re: Issues with MAT reading AdoptJDK openj9 core.dmp files [message #1843285 is a reply to message #1843284]

Thu, 22 July 2021 10:47

Eclipse User

Good morning Andrew,

First, thanks for a quick response.

So, if I interpret your response correctly, no way to read the thread stack traces, etc. via MAT. Correct?

Thanks,
Rich

Re: Issues with MAT reading AdoptJDK openj9 core.dmp files [message #1843286 is a reply to message #1843285]

Thu, 22 July 2021 11:39

Eclipse User

jdmpview -core yourcorefile.dmp
info thread

might help you see the stacks.
In MAT as the thread stacks are not correct then the thread locals would not be correctly marked as roots and various objects could be discarded from the snapshot. keep_unreachable_objects might help in that situation, but it is going to be harder to spot a leak.

Re: Issues with MAT reading AdoptJDK openj9 core.dmp files [message #1843317 is a reply to message #1843286]

Fri, 23 July 2021 08:53

Eclipse User

Thanks, Andrew! I just read your note.

Yesterday, I used jdmpview>info thread * generating an output file. I can correlate data using in the javacore, info thread output and MAT's help reading the core.dmp file. Yes, imperfect , but at least we can begin to determine what the end users maybe running via the thread stack traces. Also, if a thread's retaining high heap values we can troubleshoot.

IMO, at least a good workaround

Thanks again!

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