8361827: [TESTBUG] serviceability/HeapDump/UnmountedVThreadNativeMethodAtTop.java throws OutOfMemoryError

[reinrich]

This pr makes sure to call System.gc() before each test in UnmountedVThreadNativeMethodAtTop.java

The intention is to get rid of unreachable objects representing loaded heap dumps from previous tests.

It prevents OutOfMemoryErrors and parsing the smaller dumps is faster.

The PR also includes a reproducer for convenient testing of the pr.

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8361827: [TESTBUG] serviceability/HeapDump/UnmountedVThreadNativeMethodAtTop.java throws OutOfMemoryError (Bug - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/26260/head:pull/26260
$ git checkout pull/26260

Update a local copy of the PR:
$ git checkout pull/26260
$ git pull https://git.openjdk.org/jdk.git pull/26260/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 26260

View PR using the GUI difftool:
$ git pr show -t 26260

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/26260.diff

[bridgekeeper]

👋 Welcome back rrich! A progress list of the required criteria for merging this PR into pr/26213 will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

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

• serviceability

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-notifier]

The parent pull request that this pull request depends on 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 8361602_TESTBUG_UnmountedVThreadNativeMethodAtTop_OOM
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# if there are conflicts, follow the instructions given by git merge
git commit -m "Merge master"
git push

[openjdk]

@reinrich this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout 8361602_TESTBUG_UnmountedVThreadNativeMethodAtTop_OOM
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[reinrich]

I'm closing this pr because I don't like how it shows the commits of the now integrated dependent pr #26213
New pr is #26278