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Merged
mcculls merged 1 commit into from
Jun 11, 2025
Merged

Improve stability of InstrumenterUnloadTest #8967

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16 changes: 13 additions & 3 deletions dd-java-agent/src/test/groovy/datadog/trace/agent/InstrumenterUnloadTest.groovy
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Original file line number Diff line number Diff line change
Expand Up @@ -26,16 +26,26 @@ class InstrumenterUnloadTest extends Specification {
, ["DD_API_KEY": API_KEY]
, new PrintStream(testOutput))

int unloadCount = 0
boolean canaryUnloaded = false
int unloadedInstrumentationCount = 0
new ByteArrayInputStream((testOutput.toByteArray())).eachLine {
System.out.println(it)
if (it =~ /(?i)unload.*Canary/) {
canaryUnloaded = true
}
if (it =~ /(?i)unload.* datadog.trace.instrumentation./) {
unloadCount++
unloadedInstrumentationCount++
}
}

if (!canaryUnloaded) {
System.out.println("WARNING: Canary class was not unloaded!")
}

then:
returnCode == 0
unloadCount > 0
// skip check if we couldn't even unload our Canary class, as that
// indicates full GC didn't happen enough to trigger any unloading
!canaryUnloaded || unloadedInstrumentationCount > 0
}
}
29 changes: 24 additions & 5 deletions dd-java-agent/src/test/java/jvmbootstraptest/UnloadingChecker.java
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Original file line number Diff line number Diff line change
@@ -1,13 +1,32 @@
package jvmbootstraptest;

import static java.util.concurrent.TimeUnit.MINUTES;

import datadog.trace.test.util.GCUtils;
import java.lang.management.ClassLoadingMXBean;
import java.lang.management.ManagementFactory;

public class UnloadingChecker {
public static void main(final String[] args) {
try {
GCUtils.awaitGC();
} catch (InterruptedException e) {
e.printStackTrace();
static class Canary {}

public static void main(final String[] args) throws Exception {
ClassLoadingMXBean classLoadingMXBean = ManagementFactory.getClassLoadingMXBean();
long initialUnloadCount = classLoadingMXBean.getUnloadedClassCount();

// load an isolated class which we know can be unloaded after a full GC
new IsolatingClassLoader().loadClass("jvmbootstraptest.UnloadingChecker$Canary");
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@dougqh dougqh Jun 11, 2025 •
edited
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Nice. I was considering something similar inside GCUtils.
Specifically, I was thinking a PhantomReference to an isolated Class, then verify unloading via a ReferenceQueue.

That would at least provide some indication that classes were collection rather than a random Object.


long waitNanos = MINUTES.toNanos(2);
long startNanos = System.nanoTime();

while (System.nanoTime() - startNanos < waitNanos) {
try {
GCUtils.awaitGC();
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@jpbempel jpbempel Jun 11, 2025

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I would call directly System.gc() here
awaitGC is still fundamentally flawed because of weak reference

} catch (Throwable ignore) {
}
if (initialUnloadCount < classLoadingMXBean.getUnloadedClassCount()) {
break; // some class unloading has taken place, stop and check results
}
}
}
}
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