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[Fix #138] Avoid SnapshotImpl.getObject HeapObjectCache thrashing in getRetainedHeapTopConsumersDescription #139

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[Fix #138] Avoid SnapshotImpl.getObject HeapObjectCache thrashing in getRetainedHeapTopConsumersDescription #139

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38 changes: 19 additions & 19 deletions plugins/org.eclipse.mat.api/src/org/eclipse/mat/inspections/LeakHunterQuery.java
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Original file line number Diff line number Diff line change
Expand Up @@ -632,25 +632,26 @@ private String getRetainedHeapTopConsumersDescription(int[] objects, IProgressLi
{ return Messages.LeakHunterQuery_RetainedHeapComponentEmpty; }
int[] minRetainedSet = snapshot.getMinRetainedSet(objects, listener);

Map<String, Long> sumHeapSizes = new HashMap<>();
Map<String, Integer> counts = new HashMap<>();
Map<Integer, Long> sumHeapSizes = new HashMap<>();
Map<Integer, Integer> counts = new HashMap<>();
Comment on lines +635 to +636
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@jasonk000 jasonk000 Aug 20, 2025

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We also have org.eclipse.mat.collect.HashMapIntLong as an option, to avoid the boxing.

for (int objectId : minRetainedSet)
{
IObject object = snapshot.getObject(objectId);
String name = snapshot.isClass(objectId) ? ((IClass) object).getName() : object.getClazz().getName();
sumHeapSizes.merge(name, snapshot.getHeapSize(objectId), Long::sum);
counts.merge(name, 1, Integer::sum);
if (listener.isCanceled())
throw new IProgressListener.OperationCanceledException();
Integer key = snapshot.isClass(objectId) ? objectId : snapshot.getClassOf(objectId).getObjectId();
sumHeapSizes.merge(key, snapshot.getHeapSize(objectId), Long::sum);
counts.merge(key, 1, Integer::sum);
}
StringBuilder result = new StringBuilder();
Set<Entry<String, Long>> entries = sumHeapSizes.entrySet();
Set<Entry<Integer, Long>> entries = sumHeapSizes.entrySet();
boolean multipleItems = entries.size() > 1 && topItems > 1;
PriorityQueue<Entry<String, Long>> pq = new PriorityQueue<Entry<String, Long>>(entries.size(),
PriorityQueue<Entry<Integer, Long>> pq = new PriorityQueue<Entry<Integer, Long>>(entries.size(),
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@jasonk000 jasonk000 Aug 20, 2025

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In hindsight, wondering if you found this PQ better than a sort?

(e1, e2) -> e2.getValue().compareTo(e1.getValue()));
pq.addAll(entries);
int maxItems = Math.min(pq.size(), topItems);
while (maxItems-- > 0 && pq.size() > 0)
{
Entry<String, Long> entry = pq.poll();
Entry<Integer, Long> entry = pq.poll();
if (result.length() > 0)
{
result.append(", "); //$NON-NLS-1$
Expand All @@ -660,16 +661,15 @@ private String getRetainedHeapTopConsumersDescription(int[] objects, IProgressLi
result.append(Messages.LeakHunterQuery_RetainedHeapComponentAnd);
}
int count = counts.get(entry.getKey());
if (count == 1)
{
result.append(MessageUtil.format(Messages.LeakHunterQuery_RetainedHeapComponentInstance,
HTMLUtils.escapeText(entry.getKey()), count, bytesFormatter.format(entry.getValue())));
}
else
{
result.append(MessageUtil.format(Messages.LeakHunterQuery_RetainedHeapComponentInstances,
HTMLUtils.escapeText(entry.getKey()), count, bytesFormatter.format(entry.getValue())));
}

int objectId = entry.getKey();
IObject object = snapshot.getObject(objectId);
String name = snapshot.isClass(objectId) ? ((IClass) object).getName() : object.getClazz().getName();

result.append(MessageUtil.format(
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@jasonk000 jasonk000 Aug 20, 2025

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😎 great

count == 1 ? Messages.LeakHunterQuery_RetainedHeapComponentInstance
: Messages.LeakHunterQuery_RetainedHeapComponentInstances,
HTMLUtils.escapeText(name), count, bytesFormatter.format(entry.getValue())));
}
return result.toString();
}
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5 changes: 4 additions & 1 deletion plugins/org.eclipse.mat.api/src/org/eclipse/mat/snapshot/ISnapshot.java
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Expand Up @@ -501,7 +501,10 @@ public DominatorsSummary getDominatorsOf(int[] objectIds, Pattern excludePattern
* Get object abstracting the real Java Object from the heap dump identified
* by the given id.
* <p>
* Performance: Relatively fast - single index operation.
* Performance: Relatively fast - single index operation; however, there
* may be a fixed size cache of objects and heavy use of this method can induce
* overhead in cache management. When possible, prefer to use {@code objectId}
* until absolutely necessary to gather object information.
*
* @param objectId
* id of object you want a convenient object abstraction for
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