8271514: support JFR use of new ThreadsList::Iterator #4949

dcubed-ojdk · 2021-07-30T20:20:48Z

A trivial fix to support JFR use of new ThreadsList::Iterator.

This fix was tested with Mach5 Tier[1-3].

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Issue

JDK-8271514: support JFR use of new ThreadsList::Iterator

Reviewers

Serguei Spitsyn (@sspitsyn - Reviewer) ⚠️ Review applies to 3c64ea2
Markus Grönlund (@mgronlun - Reviewer)

Contributors

Kim Barrett <kbarrett@openjdk.org>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/4949/head:pull/4949
$ git checkout pull/4949

Update a local copy of the PR:
$ git checkout pull/4949
$ git pull https://git.openjdk.java.net/jdk pull/4949/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 4949

View PR using the GUI difftool:
$ git pr show -t 4949

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/4949.diff

…res.

…adsList::Iterator

bridgekeeper · 2021-07-30T20:21:11Z

👋 Welcome back dcubed! 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 · 2021-07-30T20:23:32Z

@dcubed-ojdk 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.

openjdk · 2021-07-30T21:03:19Z

⚠️ @dcubed-ojdk This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).

dcubed-ojdk · 2021-07-31T03:31:25Z

/label remove hotspot

/label add hotspot-runtime
/label add serviceability

openjdk · 2021-07-31T03:32:49Z

@dcubed-ojdk
The hotspot label was successfully removed.

openjdk · 2021-07-31T03:33:55Z

@dcubed-ojdk
The hotspot-runtime label was successfully added.

openjdk · 2021-07-31T03:34:56Z

@dcubed-ojdk
The serviceability label was successfully added.

mlbridge · 2021-07-31T14:30:45Z

Webrevs

dcubed-ojdk · 2021-07-31T14:33:22Z

/contributor add @kimbarrett

openjdk · 2021-07-31T14:34:09Z

@dcubed-ojdk
Contributor Kim Barrett <kbarrett@openjdk.org> successfully added.

dholmes-ora

Hi Dan,

I'm assuming that the intent of this conversion is that JavaThreadIteratorWithHandle is going to be removed - is that right?

The conversion seems okay but definitely not a trivial change IMO. And a query below before I can approve this.

Thanks,
David

dholmes-ora · 2021-08-02T04:32:31Z

src/hotspot/share/jfr/utilities/jfrThreadIterator.hpp

@@ -47,15 +47,17 @@ class JfrThreadIterator : public AP {

 class JfrJavaThreadIteratorAdapter {
 private:
-  JavaThreadIteratorWithHandle _iter;
-  JavaThread* _next;
+  ThreadsListHandle _tlist;


Why do we need to store this?

It looks very suspiocious to have a member that is a stackObj, in a class that is not itself a stackObj. ??

The _tlist is used locally in JfrJavaThreadIteratorAdapter constructor only, so it is possible to get rid of it for the price of complicating the constructor a little bit.

The _tlist is a handle that ensures the captured ThreadsList remains live while the iterator (or a copy) exists. Dropping it would leave _it and _end potentially dangling.

Okay I had assumed there was a ThreadsList/Handle in the enclosing scope that was being used to initialize this and keep things live, but that is not the case.
I still think it makes no sense to have a StackObj subtype as a member though. Maybe ThreadsListHandle should no longer be a StackObj ?

This isn't a change wrto StackObj usage. This adapter class used to have a member that was a JavaThreadIteratorWithHandle (the WithHandle class for the same reason the new code has a ThreadsListHandle, to keep the associated ThreadsList alive), which also derives from StackObj.

Personally, I want to agree with you. I would (and do) use StackObj far more sparingly than it appears in our code base. But I've had this same argument with other folks. The de facto situation, so far as I understand it, is that deriving from StackObj documents normal usage. It has no operational behavior or additional semantics, other than attempting to prevent heap allocation (and it doesn't really succeed there, since a derived class could override that behavior, though I don't currently know of any that do so). That seems to be what some people want from it and think is useful, and I've stopped trying to convince them otherwise.

The JfrThreadIterator is only used as a stack-allocated object, so it and the adapters can be decorated with StackObj to better communicate this intent. The AP (Allocation Policy) policy in JfrThreadIterator can be removed and the JfrThreadIterator can be decorated with StackObj (unconditionally). Depends on how much you want to spend on this (I would guess minimal). But in actual usages, the iterators and adapters are de-facto StackObj already.

Ah I didn't realise JTIWH was also stackObj.

The thing with StackObj to me is that it indicates a local object that does something interesting on construction and then also on destruction (eg. like MutexLocker). So having one as a member where the destruction is not related to a stack scope seems odd to me. But a stackObj member in a stackObj class seems more reasonable.

StackObj to me communicates intent. I don't have to look for "new SomeClass" to see how it is allocated and deallocated, since the new and delete operator are private and won't compile. Same is true for AllStatic. I'm one that hasn't been convinced otherwise. I'm not totally intransigent though as i approved the removal of ValueObj. So there's that.

sspitsyn

Hi Dan,
It looks good to me modulo the question from David.
Thanks,
Serguei

kimbarrett · 2021-08-05T04:05:19Z

I'm assuming that the intent of this conversion is that JavaThreadIteratorWithHandle is going to be removed - is that right?

That was my intent. But this is a somewhat complicated use, so dealing with it separately. And I agree this is not a trivial change.

openjdk-notifier · 2021-08-06T14:21:19Z

The dependent pull request has now been integrated, and the target branch of this pull request has been updated. This means that changes from the dependent pull request can start to show up as belonging to this pull request, which may be confusing for reviewers. To remedy this situation, simply merge the latest changes from the new target branch into this pull request by running commands similar to these in the local repository for your personal fork:

git checkout JDK-8271513
git fetch https://git.openjdk.java.net/jdk master
git merge FETCH_HEAD
# if there are conflicts, follow the instructions given by git merge
git commit -m "Merge master"
git push

openjdk · 2021-08-06T14:22:32Z

@dcubed-ojdk 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:

8271514: support JFR use of new ThreadsList::Iterator

Co-authored-by: Kim Barrett <kbarrett@openjdk.org>
Reviewed-by: sspitsyn, mgronlun

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 9 new commits pushed to the master branch:

d04d4ee: 8274894: Use Optional.empty() instead of ofNullable(null) in HttpResponse.BodySubscribers.discarding
33050f8: 8274986: max code printed in hs-err logs should be configurable
8de2636: 8274615: Support relaxed atomic add for linux-aarch64
7d2633f: 8275002: Remove unused AbstractStringBuilder.MAX_ARRAY_SIZE
cfe7471: 8177814: jdk/editpad is not in jdk TEST.groups
a5f09d1: 8275031: runtime/ErrorHandling/MachCodeFramesInErrorFile.java fails when hsdis is present
ef0922e: 8274560: JFR: Add test for OldObjectSample event when using Shenandoah
1e30695: 8274466: G1: use field directly rather than method in G1CollectorState::in_mixed_phase
dd93c6e: 8272167: AbsPathsInImage.java should skip *.dSYM directories

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

bridgekeeper · 2021-09-03T17:06:23Z

@dcubed-ojdk This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

dcubed-ojdk · 2021-10-11T22:16:09Z

Rebased this project to the latest jdk/jdk baseline as of 2021.10.11 in the afternoon.

This PR needs a review from either @mgronlun or @egahlin since I'm changing
JFR code here.

dcubed-ojdk · 2021-10-11T22:16:36Z

The rebase has passed Mach5 Tier1 testing; Mach5 Tier[23] are in process.

Update: Mach5 Tier[23] test also passed.

mgronlun

Looks good Dan, thank you.

dcubed-ojdk · 2021-10-12T17:04:24Z

@sspitsyn and @mgronlun - Thanks for the reviews.

/integrate

openjdk · 2021-10-12T17:05:55Z

Going to push as commit 8657f77.
Since your change was applied there have been 17 commits pushed to the master branch:

b8bd259: 8271737: Only normalize the cached user.dir property once
89999f7: 8275131: Exceptions after a touchpad gesture on macOS
07b1f1c: 8274548: (fc) FileChannel gathering write fails with IOException "Invalid argument" on macOS 11.6
f623460: 8274911: testlibrary_tests/ir_framework/tests/TestIRMatching.java fails with "java.lang.RuntimeException: Should have thrown exception"
e393c5e: 8275074: Cleanup unused code in JFR LeakProfiler
e16b93a: 8274770: [PPC64] resolve_jobject needs a generic implementation to support load barriers
1ab6414: 8275051: Shenandoah: Correct ordering of requested gc cause and gc request flag
b460d6d: 8275091: /src/jdk.management.jfr/share/classes/module-info.java has non-canonical order
d04d4ee: 8274894: Use Optional.empty() instead of ofNullable(null) in HttpResponse.BodySubscribers.discarding
33050f8: 8274986: max code printed in hs-err logs should be configurable
... and 7 more: https://git.openjdk.java.net/jdk/compare/829dea45c9ab90518f03a66aad7e681cd4fda8b3...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-10-12T17:06:10Z

@dcubed-ojdk Pushed as commit 8657f77.

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

dcubed-ojdk added 6 commits Jul 1, 2021

8193559.cr0

3f653c5

kbarrett CR - delete unused _list member.

5ee4991

Merge branch 'master' into JDK-8193559

a133ca4

8193559.kbarrett.part1 - Kim's proposed rewrite using newer C++ featu…

3be5dc7

…res.

8271513: support JavaThreadIteratorWithHandle replacement by new Thre…

8c255c4

…adsList::Iterator

8271514: support JFR use of new ThreadsList::Iterator

6254eca

openjdk bot added the hotspot label Jul 30, 2021

dcubed-ojdk added 3 commits Jul 30, 2021

kbarrett CR - simplify 'ThreadsList::Iterator::operator!=(Iterator i)'

a8865b8

Merge branch 'pull/4671' into JDK-8271513

b3edb5c

Merge branch 'pull/4948' into JDK-8271514

056badc

dcubed-ojdk changed the base branch from master to pr/4671 Jul 30, 2021

dcubed-ojdk changed the base branch from pr/4671 to pr/4948 Jul 30, 2021

openjdk bot removed the hotspot label Jul 31, 2021

openjdk bot added the hotspot-runtime label Jul 31, 2021

openjdk bot added the serviceability label Jul 31, 2021

dcubed-ojdk marked this pull request as ready for review Jul 31, 2021

openjdk bot added the rfr label Jul 31, 2021

dholmes-ora reviewed Aug 2, 2021

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dcubed-ojdk added 2 commits Aug 2, 2021

Merge branch 'master' into JDK-8271513

733faa7

Merge branch 'pull/4948' into JDK-8271514

3c64ea2

sspitsyn approved these changes Aug 4, 2021

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openjdk-notifier bot changed the base branch from pr/4948 to master Aug 6, 2021

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Merge branch 'master' into JDK-8271514

8873ddd

dcubed-ojdk added 2 commits Sep 22, 2021

Merge branch 'master' into JDK-8271514

76d44dc

Merge branch 'master' into JDK-8271514

a2e39c3

mgronlun approved these changes Oct 12, 2021

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openjdk bot closed this Oct 12, 2021

openjdk bot added integrated and removed ready rfr labels Oct 12, 2021

dcubed-ojdk deleted the JDK-8271514 branch Oct 12, 2021

8271514: support JFR use of new ThreadsList::Iterator #4949

8271514: support JFR use of new ThreadsList::Iterator #4949

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8271514: support JFR use of new ThreadsList::Iterator #4949

8271514: support JFR use of new ThreadsList::Iterator #4949

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