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https://issues.apache.org/jira/browse/GROOVY-12579?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18136182#comment-18136182
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ASF GitHub Bot commented on GROOVY-12579:
-----------------------------------------
paulk-asert merged PR #3095:
URL: https://github.com/apache/groovy/pull/3095
> Class loaders of discarded scripts stay reachable through method handle
> caches on JDK 17
> ----------------------------------------------------------------------------------------
>
> Key: GROOVY-12579
> URL: https://issues.apache.org/jira/browse/GROOVY-12579
> Project: Groovy
> Issue Type: Bug
> Components: groovy-runtime
> Affects Versions: 4.0.33, 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> {{MethodHandle.asType}} caches its result on the handle converted. JDK 17
> keeps that cache as a strong reference to the last conversion; JDK 18 and
> later keep a conversion strongly only when the handle's own types keep the
> classes of the new type reachable. Linking an indy call site converts handles
> to the call site type, so on JDK 17 a handle that outlives the call site
> keeps the classes of that type, and their class loader, reachable:
> * a cast converts {{MethodHandles.identity(Object.class)}}, which the JDK
> shares across the JVM;
> * {{catchException}} converts the JDK's shared argument-array collector to
> the type of its target, which every linked method call goes through;
> * the guard and filter handles in static fields of the runtime ({{IS_NULL}},
> {{NON_NULL}}, {{UNWRAP_METHOD}}, and the handle being cast at the end of
> linking).
> A script in a {{GroovyClassLoader}} that casts to its own class is therefore
> never released on JDK 17:
> {code:groovy}
> import java.lang.ref.WeakReference
> import groovy.transform.CompileStatic
> @CompileStatic
> WeakReference<ClassLoader> runDiscarded() {
> def loader = new GroovyClassLoader(this.class.classLoader)
> Script script = (Script) loader.parseClass('''
> class Holder { String label = 'h'; Holder self(Holder o) { o ?: this
> } }
> def held = new Holder()
> Holder holder = held
> holder.self(null).label
> ''').getDeclaredConstructor().newInstance()
> script.run()
> script = null
> loader.close()
> new WeakReference<ClassLoader>(loader)
> }
> @CompileStatic
> boolean collected(WeakReference<ClassLoader> ref) {
> for (int i = 0; i < 100; i++) {
> System.gc()
> if (i % 50 == 10) {
> try { List<byte[]> hog = []; while (true) hog << new byte[(int)
> Math.max(1024L, Runtime.runtime.freeMemory() >> 2)] } catch (OutOfMemoryError
> ignored) { }
> }
> if (ref.get() == null) return true
> Thread.sleep(10)
> }
> false
> }
> println "collected: ${collected(runDiscarded())}" // -Xmx256m: false on JDK
> 17, true on JDK 21
> {code}
> The class loader cleanup that the integration guide documents ends with such
> a cast, so on JDK 17 it does not release the class loader of the Groovy copy
> it cleans up either.
> PR: https://github.com/apache/groovy/pull/3095
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