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8289284: jdk.tracePinnedThreads output confusing when pinned due to native frame #9308

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@AlanBateman AlanBateman commented Jun 28, 2022

The system property jdk.tracePinnedThreads triggers a stack trace to be printed when a virtual thread parks while pinned. If a virtual thread is pinned due to a native frame there is a spurious " <== monitors:0" added to line for the native method.

A secondary issue is that there is no stack trace when there is Panama downcall as there isn't a native method in the stack trace. A future change may annotate the downcalls, for now the entire stack trace is printed (no filtering) so there is at least some output when pinned due to a call through native code


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  • JDK-8289284: jdk.tracePinnedThreads output confusing when pinned due to native frame

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👋 Welcome back alanb! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

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@AlanBateman The following labels will be automatically applied to this pull request:

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@openjdk openjdk bot added build build-dev@openjdk.org core-libs core-libs-dev@openjdk.org labels Jun 28, 2022
@AlanBateman AlanBateman marked this pull request as ready for review June 28, 2022 14:12
@openjdk openjdk bot added the rfr Pull request is ready for review label Jun 28, 2022
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Webrevs

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/label remove build

@openjdk openjdk bot removed the build build-dev@openjdk.org label Jun 28, 2022
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jaikiran commented Jul 12, 2022

Hello Alan,
The changes looks fine to me. I'm not too familiar with the build files, so I can't comment about the changes to the JtregNativeJdk.gmk file.

On a slightly related note, while reviewing this change, I noticed the code in VirtualThread here https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/VirtualThread.java#L177. Is it intentional that we don't print/use the reason while printing out the stacktrace? The reason appears to be one of:

/** Native frame on stack */ NATIVE,
        /** Monitor held */          MONITOR,
        /** In critical section */   CRITICAL_SECTION

Would printing this reason be useful for easily understanding why the thread was considered pinned? I guess the same could be inferred from the stacktraces right now?

}
}).join();
System.out.flush();
VThreadRunner.run(task::run);
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The change here removes the previous call to flush the System.out. I believe that's fine because the PrintStream here is backed by a ByteArrayOutputStream so the flush isn't necessary.

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The change here removes the previous call to flush the System.out. I believe that's fine because the PrintStream here is backed by a ByteArrayOutputStream so the flush isn't necessary.

That's a good observation, it would be more robust for the test to create the PrintStream with "auto flush" or use an explicit flush. It works now because there is sufficient output to trigger flushing. So I'll change this to auto flush - thanks!

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openjdk bot commented Jul 12, 2022

@AlanBateman This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8289284: jdk.tracePinnedThreads output confusing when pinned due to native frame

Reviewed-by: jpai, mchung

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At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

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Looks fine to me.

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Would printing this reason be useful for easily understanding why the thread was considered pinned? I guess the same could be inferred from the stacktraces right now?

The stack trace shows the native frames and highlights any frames with monitors. So the "reason" isn't currently needed.

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Thank you for the update. This looks fine to me.

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/integrate

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openjdk bot commented Jul 13, 2022

Going to push as commit f528124.
Since your change was applied there has been 1 commit pushed to the master branch:

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Jul 13, 2022
@openjdk openjdk bot closed this Jul 13, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jul 13, 2022
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@AlanBateman Pushed as commit f528124.

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