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Fix unresolved sticky class GC roots #9497

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Fix unresolved sticky class GC roots #9497

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4f123fb
Fix #6357: unresolved sticky class GC roots
wilx Jul 5, 2026
66beb5d
Fix #6357: retain sticky class GC roots by ID
wilx Jul 10, 2026
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20 changes: 10 additions & 10 deletions profiler/lib.profiler/src/org/netbeans/lib/profiler/heap/HprofGCRoots.java
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Original file line number Diff line number Diff line change
Expand Up @@ -39,16 +39,16 @@ class HprofGCRoots {
private final Object lastThreadObjGCLock = new Object();
private Map<Long,GCRoot> gcRoots;
private final Object gcRootLock = new Object();
private List gcRootsList;
private List<HprofGCRoot> gcRootsList;

HprofGCRoots(HprofHeap h) {
heap = h;
}

Collection<GCRoot> getGCRoots() {
Collection<HprofGCRoot> getGCRoots() {
synchronized (gcRootLock) {
if (gcRoots == null) {
List<GCRoot> rootList = new ArrayList<>();
List<HprofGCRoot> rootList = new ArrayList<>();
computeGCRootsFor(heap.getHeapTagBound(HprofHeap.ROOT_UNKNOWN), rootList);
computeGCRootsFor(heap.getHeapTagBound(HprofHeap.ROOT_JNI_GLOBAL), rootList);
computeGCRootsFor(heap.getHeapTagBound(HprofHeap.ROOT_JNI_LOCAL), rootList);
Expand All @@ -67,10 +67,8 @@ Collection<GCRoot> getGCRoots() {
computeGCRootsFor(heap.getHeapTagBound(HprofHeap.ROOT_VM_INTERNAL), rootList);
computeGCRootsFor(heap.getHeapTagBound(HprofHeap.ROOT_JNI_MONITOR), rootList);

rootList.sort(new Comparator() {
public int compare(Object o1, Object o2) {
HprofGCRoot r1 = (HprofGCRoot) o1;
HprofGCRoot r2 = (HprofGCRoot) o2;
rootList.sort(new Comparator<HprofGCRoot>() {
public int compare(HprofGCRoot r1, HprofGCRoot r2) {
int kind = r1.getKind().compareTo(r2.getKind());

if (kind != 0) {
Expand All @@ -92,8 +90,10 @@ GCRoot getGCRoot(Long instanceId) {
if (gcRoots == null) {
heap.getGCRoots();
roots = new HashMap<>();
for (GCRoot r : getGCRoots()) {
roots.put(r.getInstance().getInstanceId(), r);
for (HprofGCRoot root : getGCRoots()) {
// A GC root is identified by its HPROF ID. Some valid root
// records do not have a corresponding heap Instance.
roots.put(root.getInstanceId(), root);
}
gcRoots = roots;
} else {
Expand Down Expand Up @@ -126,7 +126,7 @@ ThreadObjectGCRoot getThreadGCRoot(int threadSerialNumber) {
return map.get(threadSerialNumber);
}

private void computeGCRootsFor(TagBounds tagBounds, Collection<GCRoot> roots) {
private void computeGCRootsFor(TagBounds tagBounds, Collection<HprofGCRoot> roots) {
if (tagBounds != null) {
int rootTag = tagBounds.tag;
long[] offset = new long[]{tagBounds.startOffset};
Expand Down
63 changes: 63 additions & 0 deletions profiler/lib.profiler/test/unit/src/org/netbeans/lib/profiler/heap/HeapSegmentTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,8 @@
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertTrue;
import org.junit.Test;
import org.netbeans.lib.profiler.heap.HeapUtils.HprofGenerator;

Expand All @@ -45,6 +47,67 @@ public void singleObjectMultipleSegments() throws IOException {
singleObject(true);
}

@Test
public void stickyClassRootKeepsStaticReferencesReachable() throws IOException {
File mydump = File.createTempFile("mydump", ".hprof");
final int[] targetId = new int[1];
try (HprofGenerator gen = new HprofGenerator(new FileOutputStream(mydump))) {
gen.writeHeapSegment(new HprofGenerator.Generator<HprofGenerator.HeapSegment>() {
@Override
public void generate(HprofGenerator.HeapSegment seg) throws IOException {
seg.newClass("java.lang.Class").dumpClass();
seg.newClass("com.oracle.svm.core.heap.heapImpl.DiscoverableReference")
.addField("rawReferent", Object.class)
.dumpClass();
HprofGenerator.ClassInstance targetClass = seg.newClass("text.Target").dumpClass();
targetId[0] = seg.dumpInstance(targetClass);
HprofGenerator.ClassInstance rootClass = seg.newClass("text.Root")
.addStaticObjectField("target", targetId[0])
.dumpClass();
seg.dumpStickyClassRoot(rootClass);
}
}, true);
}

Heap heap = HeapFactory.createHeap(mydump);
assertEquals("One sticky class root", 1, heap.getGCRoots().size());
GCRoot root = (GCRoot) heap.getGCRoots().iterator().next();
Instance rootInstance = root.getInstance();
assertTrue("Class object instance", rootInstance instanceof ClassDumpInstance);
assertEquals("Root found by class object ID", root, heap.getGCRoot(rootInstance));

Instance target = heap.getInstanceByID(targetId[0]);
assertNotNull("Static field target", target);
heap.getBiggestObjectsByRetainedSize(1);
assertEquals("Target reached from sticky class", rootInstance, target.getNearestGCRootPointer());
assertTrue("Sticky class retains its static target", rootInstance.getRetainedSize() > rootInstance.getSize());
}

@Test
public void unresolvedStickyClassRootDoesNotBreakRetainedSize() throws IOException {
File mydump = File.createTempFile("mydump", ".hprof");
try (HprofGenerator gen = new HprofGenerator(new FileOutputStream(mydump))) {
gen.writeHeapSegment(new HprofGenerator.Generator<HprofGenerator.HeapSegment>() {
@Override
public void generate(HprofGenerator.HeapSegment seg) throws IOException {
seg.newClass("java.lang.Class").dumpClass();
seg.newClass("com.oracle.svm.core.heap.heapImpl.DiscoverableReference")
.addField("rawReferent", Object.class)
.dumpClass();
HprofGenerator.ClassInstance ordinaryClass = seg.newClass("text.Ordinary").dumpClass();
seg.dumpInstance(ordinaryClass);
seg.dumpStickyClassRoot(Integer.MAX_VALUE);
}
}, true);
}

Heap heap = HeapFactory.createHeap(mydump);
assertEquals("One unresolved sticky class root", 1, heap.getGCRoots().size());
GCRoot root = (GCRoot) heap.getGCRoots().iterator().next();
assertNull("No heap object for unresolved root", root.getInstance());
assertNotNull("Retained-size computation completes", heap.getBiggestObjectsByRetainedSize(1));
}

private static void singleObject(boolean flush) throws IOException {
File mydump = File.createTempFile("mydump", ".hprof");
Heap heap = generateSampleDump(mydump, flush);
Expand Down
23 changes: 22 additions & 1 deletion profiler/lib.profiler/test/unit/src/org/netbeans/lib/profiler/heap/HeapUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,15 @@ public int dumpPrimitive(Object obj) throws IOException {
return instanceId;
}

public void dumpStickyClassRoot(ClassInstance clazz) throws IOException {
dumpStickyClassRoot(clazz.id);
}

public void dumpStickyClassRoot(int classId) throws IOException {
heap.writeByte(0x05);
heap.writeInt(classId);
}

public final class ThreadBuilder {

private String groupName;
Expand Down Expand Up @@ -235,6 +244,7 @@ public final class ClassBuilder {

private final int classId;
private TreeMap<String, Class<?>> fieldNamesAndTypes = new TreeMap<>();
private TreeMap<String, Integer> staticObjectFields = new TreeMap<>();

private ClassBuilder(int id) {
this.classId = id;
Expand All @@ -245,6 +255,11 @@ public ClassBuilder addField(String name, Class<?> type) {
return this;
}

public ClassBuilder addStaticObjectField(String name, int instanceId) {
staticObjectFields.put(name, instanceId);
return this;
}

public ClassInstance dumpClass() throws IOException {
heap.writeByte(0x20);
heap.writeInt(classId); // class ID
Expand All @@ -257,7 +272,12 @@ public ClassInstance dumpClass() throws IOException {
heap.writeInt(0); // reserved 2
heap.writeInt(0); // instance size
heap.writeShort(0); // # of constant pool entries
heap.writeShort(0); // # of static fields
heap.writeShort(staticObjectFields.size()); // # of static fields
for (Map.Entry<String, Integer> entry : staticObjectFields.entrySet()) {
heap.writeInt(writeString(entry.getKey()));
heap.writeByte(0x02); // object
heap.writeInt(entry.getValue());
}
heap.writeShort(fieldNamesAndTypes.size()); // # of instance fields
int fieldBytes = 0;
for (Map.Entry<String, Class<?>> entry : fieldNamesAndTypes.entrySet()) {
Expand Down Expand Up @@ -299,6 +319,7 @@ public ClassInstance dumpClass() throws IOException {
}
ClassInstance inst = new ClassInstance(classId, fieldNamesAndTypes, fieldBytes);
fieldNamesAndTypes = new TreeMap<>();
staticObjectFields = new TreeMap<>();
return inst;
}
}
Expand Down