8358750: JFR: EventInstrumentation MASK_THROTTLE* constants should be computed in longs

[egahlin]

Could I have a review of a fix to the throttling mechanism added in JDK 25? Long values should be shifted instead of integer values when creating the masks.

During debugging, I found several issues, and I also strengthened the test.

• The start time of the event needs to be stored if the event is being throttled. The reason is that the timestamp is reused later to determine if the event should be throttled or not. This happens with events that lack an end time.

• The duration value that is written to the buffer must remove the mask if it is throttled. This is handled bygetDuration(blockCodeBuilder).

• I added a clarifying comment that when duration is compared to 0, it also prevents a new duration from being calculated if the event has been throttled (for an instant event).

The test now checks that the duration is not negative, that the start time is not before the test starts, and that the duration is not unreasonably large. The reason I multiply the recording duration by two is to give the test some slack in case we run into clock issues where the time taken for the event doesn't match the recording. Purpose of the check is to make sure we don't end up with the mask being added to the duration.

Testing:
test/jdk/jdk/jfr + tier1

I validated manually that the throttle rate works using a small test program I have (which can't be checked in due to stability issues).

---

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Issue

• JDK-8358750: JFR: EventInstrumentation MASK_THROTTLE* constants should be computed in longs (Bug - P3)

Reviewers

• Markus Grönlund (@mgronlun - Reviewer)

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[openjdk]

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

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8358750: JFR: EventInstrumentation MASK_THROTTLE* constants should be computed in longs

Reviewed-by: mgronlun

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At the time when this comment was updated there had been 61 new commits pushed to the master branch:

• 5e40fb6: 8277394: Remove the use of safepoint_workers in reference processor
• 2528c62: 8361198: [AIX] fix misleading error output in thread_cpu_time_unchecked
• 1be29bd: 8361060: Keep track of the origin server against which a jdk.internal.net.http.HttpConnection was constructed
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[egahlin]

/integrate

[openjdk]

Going to push as commit 77e69e0.
Since your change was applied there have been 69 commits pushed to the master branch:

• dcc7254: 8361213: J2DAnalyzer should emit the score as a decimal
• 003be0d: 8361325: Refactor ClassLoaderExt
• 2d9f032: 8360028: (fs) Path.relativize throws StringIndexOutOfBoundsException (win)
• ... and 66 more: https://git.openjdk.org/jdk/compare/ecd2d83096a1fea7d5086736306770bcffa4fdb6...master

Your commit was automatically rebased without conflicts.

[openjdk]

@egahlin Pushed as commit 77e69e0.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[egahlin]

/backport :jdk25

[openjdk]

@egahlin the backport was successfully created on the branch backport-egahlin-77e69e02-jdk25 in my personal fork of openjdk/jdk. To create a pull request with this backport targeting openjdk/jdk:jdk25, just click the following link:

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Hi all,

This pull request contains a backport of commit 77e69e02 from the openjdk/jdk repository.

The commit being backported was authored by Erik Gahlin on 3 Jul 2025 and was reviewed by Markus Grönlund.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk:

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$ git checkout backport-egahlin-77e69e02-jdk25
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$ git push https://github.com/openjdk-bots/jdk.git backport-egahlin-77e69e02-jdk25