[MCHECKSTYLE-457] memory leak in checkstyle plugin

[jira-importer]

James Nord opened MCHECKSTYLE-457 and commented

memory used by checkstyle:check mojo is not released after the mojo completes its analysis.

In a build on Jenkins an analysis of a heapdump shows that there is 180+MB retained by the JavaLanguageParser

!image-2025-04-11-12-55-18-038.png|thumbnail!

After the invocation of the mojo it is expected that memory would be relinquished.

Steps to reproduce

• clone https://github.com/jenkinsci/jenkins/
• switch to the jenkins-2.504 branch
• edit .mvn/jvm.config so it contains the following (to force running out of memory and providing a heap dump):

-Xmx500M
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=D:\source\github\cloudbees\private-jenkins

• run mvn clean verify -DskipTests

Expected results

500M should be enough to build, or if the build fails due to memory there is no memory held by mojos (for part of their actions) that have completed.

Actual Results

the build fails producing the war in the maven-war-plugin (in the war project).
Inspection of the heap shows 180MB in use by com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser classloaders

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Affects: 3.6.0

Attachments:

• image-2025-04-11-12-55-18-038.png (157.49 kB)
• screenshot-1.png (100.34 kB)

[jira-importer]

Michael Osipov commented

Interesting, we need to see whether we need to invoke some public close() to have that released. Roman Ivanov, can you help from the top of your head?

[jira-importer]

James Nord commented

I think it's more sinister in checkstyle than this.

!screenshot-1.png|thumbnail!

@SuppressWarnings({"all", "warnings", "unchecked", "unused", "cast", "CheckReturnValue", "this-escape"})
public class JavaLanguageParser extends Parser {
	static { RuntimeMetaData.checkVersion("4.13.2", RuntimeMetaData.VERSION); }

	protected static final DFA[] _decisionToDFA;
	protected static final PredictionContextCache _sharedContextCache =
		new PredictionContextCache();
...

So checkstyle uses a static cache and this is the ~160MB

[jira-importer]

Roman Ivanov commented

JavaLanguageParser is class generated by ANTLR.
we do not have any explicit cleanup, and we rely on GC to cleanup classes after it is finished to be used.
Java parser exists only in TreeWalker checkstyle module https://checkstyle.sourceforge.io/config.html#TreeWalker , so it is configuration of checkstyle.
So I presume, configuration classes are continue to be valid and accessible and GC is not cleanup them.

[jira-importer]

Michael Osipov commented

As far as I can see there basically nothing we can do from the plugin's perspective.

[jira-importer]

Roman Ivanov commented

https://github.com/checkstyle/checkstyle/blob/01e7ddc1de4cdda60a4150be401bd3af100699a3/src/main/java/com/puppycrawl/tools/checkstyle/Checker.java#L178

We have destroy method, if no extra reference stored to Treewalker, it should be marked for GC to cleanup.
Do we use it in plugin?

[jira-importer]

Michael Osipov commented

Yes, here it is:

maven-checkstyle-plugin/src/main/java/org/apache/maven/plugins/checkstyle/exec/DefaultCheckstyleExecutor.java

Line 196 in 0159511

checker.destroy();