8003216: Add JFR event indicating explicit System.gc() call

[egahlin]

Hi,

This is a continuation of a review that started before the pandemic.

In an offline discussion with Stefan Johansson, we looked into adding GC id to the SystemGC event, but it was not trivial. Still, it would make sense to have this event to see the stack trace of the System GC call. GC id can always be added as another enhancement. I added a field that indicates the status of -XX:+ExplicitGCInvokesConcurrent, to hint to users that the duration of the event may not be the time the GC took.

I only emit the event if a GC is triggered, so there is no need for a field -XX:+DisableExplicitGC which we talked about back then. The reason is that it could potentially create many events in the default configuration, for example if called every rendered frame. I also think users want to track calls that actually led to a GC. If there is a need for a second field, it could be added as another enhancement later.

Testing: tier1/tier2 + test/jdk/jdk/jfr

Thanks
Erik

---

Progress

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Error

 ⚠️ This PR only contains changes already present in the target

Issue

• JDK-8003216: Add JFR event indicating explicit System.gc() call ⚠️ Issue is not open.

Reviewers

• Jaroslav Bachorik (@jbachorik - Reviewer)
• Markus Grönlund (@mgronlun - Reviewer)
• Thomas Schatzl (@tschatzl - Reviewer)

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[bridgekeeper]

👋 Welcome back egahlin! 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.

[openjdk]

@egahlin The following label will be automatically applied to this pull request:

• hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[egahlin]

/label remove hotspot

[egahlin]

/label add hotspot-jfr

[egahlin]

/label add hotspot-gc

[openjdk]

@egahlin
The hotspot label was successfully removed.

[openjdk]

@egahlin
The hotspot-jfr label was successfully added.

[openjdk]

@egahlin
The hotspot-gc label was successfully added.

[mlbridge]

Webrevs

• 00: Full (2024439f)

[openjdk]

@egahlin This change is no longer ready for integration - check the PR body for details.

[tschatzl]

Lgtm.

[egahlin]

/integrate

[openjdk]

Going to push as commit e11f70a.
Since your change was applied there have been 27 commits pushed to the master branch:

• 2b41459: 8267073: Race between Card Redirtying and Freeing Collection Set regions results in missing remembered set entries with G1
• 7cd5a6e: 8268537: (Temporary) Disable ParallelRefProcEnabled for Parallel GC
• f716711: 8265271: JFR: Allow use of .jfc options when starting JFR
• f677163: 8266130: convert Thread-SMR stress tests from counter based to time based
• 6c552a7: 8268544: some runtime/sealedClasses tests should be run in driver mode
• f4b3170: 8268428: Test java/foreign/TestResourceScope.java fails: expected [M] but found [N]
• 6b6ff53: 8268543: some runtime/verifier tests should be run in driver mode
• 0924382: 8266766: Arrays of types that cannot be an annotation member do not yield exceptions
• d43c8a7: 8268124: Update java.lang to use switch expressions
• a187fcc: 8238197: JFR: Rework setting and getting EventHandler
• ... and 17 more: https://git.openjdk.java.net/jdk/compare/58ba48b7b88eff359683aa3271c48b18f1973282...master

Your commit was automatically rebased without conflicts.

[openjdk]

@egahlin Pushed as commit e11f70a.

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