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fix: prevent concurrent access to non-thread-safe maps in SketchBufferAggregatorHelper #20090

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fix: prevent concurrent access to non-thread-safe maps in SketchBufferAggregatorHelper #20090

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27 changes: 8 additions & 19 deletions ...a/org/apache/druid/query/aggregation/datasketches/theta/SketchBufferAggregatorHelper.java
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Original file line number Diff line number Diff line change
Expand Up @@ -19,16 +19,14 @@

package org.apache.druid.query.aggregation.datasketches.theta;

import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
import org.apache.datasketches.common.Family;
import org.apache.datasketches.memory.WritableMemory;
import org.apache.datasketches.theta.SetOperation;
import org.apache.datasketches.theta.Union;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.IdentityHashMap;
import java.util.concurrent.ConcurrentHashMap;

/**
* A helper class used by {@link SketchBufferAggregator} and {@link SketchVectorAggregator}
Expand All @@ -38,8 +36,8 @@ final class SketchBufferAggregatorHelper
{
private final int size;
private final int maxIntermediateSize;
private final IdentityHashMap<ByteBuffer, Int2ObjectMap<Union>> unions = new IdentityHashMap<>();
private final IdentityHashMap<ByteBuffer, WritableMemory> memCache = new IdentityHashMap<>();
private final ConcurrentHashMap<ByteBuffer, ConcurrentHashMap<Integer, Union>> unions = new ConcurrentHashMap<>();

@FrankChen021 FrankChen021 Aug 20, 2026

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[P1] Do not key caches by mutable ByteBuffers

ConcurrentHashMap uses ByteBuffer.equals/hashCode, which depend on the buffer's remaining contents. Union updates mutate those contents in place, changing the key hash after insertion. Subsequent unions.get(buf) calls can miss and get() returns SketchHolder.EMPTY; distinct equal-content buffers can also alias. Preserve identity/stable-key semantics while making access concurrent.

private final ConcurrentHashMap<ByteBuffer, WritableMemory> memCache = new ConcurrentHashMap<>();

public SketchBufferAggregatorHelper(final int size, final int maxIntermediateSize)
{
Expand All @@ -62,7 +60,7 @@ public void init(ByteBuffer buf, int position)
*/
public Object get(ByteBuffer buf, int position)
{
Int2ObjectMap<Union> unionMap = unions.get(buf);
ConcurrentHashMap<Integer, Union> unionMap = unions.get(buf);
Union union = unionMap != null ? unionMap.get(position) : null;
if (union == null) {
return SketchHolder.EMPTY;
Expand All @@ -82,7 +80,7 @@ public Object get(ByteBuffer buf, int position)
public void relocate(int oldPosition, int newPosition, ByteBuffer oldBuffer, ByteBuffer newBuffer)
{
createNewUnion(newBuffer, newPosition, true);
Int2ObjectMap<Union> unionMap = unions.get(oldBuffer);
ConcurrentHashMap<Integer, Union> unionMap = unions.get(oldBuffer);
if (unionMap != null) {
unionMap.remove(oldPosition);
if (unionMap.isEmpty()) {
Expand All @@ -99,7 +97,7 @@ public void relocate(int oldPosition, int newPosition, ByteBuffer oldBuffer, Byt
*/
public Union getOrCreateUnion(ByteBuffer buf, int position)
{
Int2ObjectMap<Union> unionMap = unions.get(buf);
ConcurrentHashMap<Integer, Union> unionMap = unions.get(buf);
Union union = unionMap != null ? unionMap.get(position) : null;
if (union != null) {
return union;
Expand All @@ -113,11 +111,7 @@ private Union createNewUnion(ByteBuffer buf, int position, boolean isWrapped)
Union union = isWrapped
? (Union) SetOperation.wrap(mem)
: (Union) SetOperation.builder().setNominalEntries(size).build(Family.UNION, mem);
Int2ObjectMap<Union> unionMap = unions.get(buf);
if (unionMap == null) {
unionMap = new Int2ObjectOpenHashMap<>();
unions.put(buf, unionMap);
}
ConcurrentHashMap<Integer, Union> unionMap = unions.computeIfAbsent(buf, k -> new ConcurrentHashMap<>());
unionMap.put(position, union);
return union;
}
Expand All @@ -130,11 +124,6 @@ public void clear()

private WritableMemory getMemory(ByteBuffer buffer)
{
WritableMemory mem = memCache.get(buffer);
if (mem == null) {
mem = WritableMemory.writableWrap(buffer, ByteOrder.LITTLE_ENDIAN);
memCache.put(buffer, mem);
}
return mem;
return memCache.computeIfAbsent(buffer, buf -> WritableMemory.writableWrap(buf, ByteOrder.LITTLE_ENDIAN));
}
}