[
https://issues.apache.org/jira/browse/GROOVY-12579?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18134519#comment-18134519
]
ASF GitHub Bot commented on GROOVY-12579:
-----------------------------------------
codeconsole opened a new pull request, #3095:
URL: https://github.com/apache/groovy/pull/3095
On JDK 17, linking a call site no longer leaves the call site's types in the
`asType` cache of a method handle that outlives it: the JDK's shared identity
handle (used for casts) and argument collector (used by `catchException`), and
the runtime's static guard and filter handles. JDK 17 keeps that cache
strongly, so a cast to a class of a discarded script or Groovy copy kept its
class loader reachable. JDK 18 and later take the unchanged path.
On JDK 17 these conversions are now made on a new handle that invokes the
long-lived one and that only the call site holds, and `catchException` is
applied to the target with its reference types erased (after making a varargs
target fixed arity), so the JDK's collector is converted to a type of JDK
classes only.
Tests:
`bugs.Groovy12142.testDynamicCallsKeepNoDiscardedScriptLoaderReachable` runs a
script with casts, typed receivers, null arguments, null-safe calls and a
failing call in a `GroovyClassLoader` and checks that the loader is collected
once dropped; it fails on JDK 17 without the change. The `groovy`, `gls`,
`bugs` and `org.codehaus.groovy` packages pass (15,496 tests). The Checkstyle
and CodeNarc gates pass. `bugs.Groovy12142` also passes on JDK 17.
Seen on JDK 17 with 4.0.33, 5.0.8 and 6.0.0.
> 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.
--
This message was sent by Atlassian Jira
(v10.3.26#10030026)
