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Collections and collection utilities for Neo4j.
There is a newer version: 5.24.0
/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.collection.trackable;

import org.eclipse.collections.impl.map.mutable.UnifiedMap;

import org.neo4j.memory.MemoryTracker;

import static java.util.Objects.requireNonNull;
import static org.neo4j.memory.HeapEstimator.ARRAY_HEADER_BYTES;
import static org.neo4j.memory.HeapEstimator.OBJECT_REFERENCE_BYTES;
import static org.neo4j.memory.HeapEstimator.alignObjectSize;
import static org.neo4j.memory.HeapEstimator.shallowSizeOfInstance;

@SuppressWarnings( "ExternalizableWithoutPublicNoArgConstructor" )
public class HeapTrackingUnifiedMap extends UnifiedMap implements AutoCloseable
{
    private static final long SHALLOW_SIZE = shallowSizeOfInstance( HeapTrackingUnifiedMap.class );
    private final MemoryTracker memoryTracker;
    private long trackedHeap;

    static  HeapTrackingUnifiedMap createUnifiedMap( MemoryTracker memoryTracker )
    {
        int initialSizeToAllocate = DEFAULT_INITIAL_CAPACITY << 2;
        long trackedHeap = arrayHeapSize( initialSizeToAllocate );
        memoryTracker.allocateHeap( SHALLOW_SIZE + trackedHeap );
        return new HeapTrackingUnifiedMap<>( memoryTracker, trackedHeap );
    }

    private HeapTrackingUnifiedMap( MemoryTracker memoryTracker, long trackedHeap )
    {
        this.memoryTracker = requireNonNull( memoryTracker );
        this.trackedHeap = trackedHeap;
    }

    @Override
    protected void allocateTable( int sizeToAllocate )
    {
        if ( memoryTracker != null )
        {
            long heapToAllocate = arrayHeapSize( sizeToAllocate );
            memoryTracker.allocateHeap( heapToAllocate );
            memoryTracker.releaseHeap( trackedHeap );
            trackedHeap = heapToAllocate;
        }
        super.allocateTable( sizeToAllocate );
    }

    @Override
    protected void rehash( int newCapacity )
    {
        super.rehash( newCapacity );
        // Add an estimated heap usage of the arrays for the chains of colliding buckets, which grow in multiples of 4 (2 key-value pairs).
        // Add a fixed cost for each chain, which amounts to an average chain length of 8 key-value pairs.
        // In actuality chains are usually much shorter, but the number of collisions is also at it lowest just after rehash and can then grow
        // substantially before the next rehash (approximately a factor of 3).
        // So based on experiments this heuristic seems to produce a fair trade-off between underestimation just before rehash and overestimation
        // just after rehash, with a bias toward more overestimation after rehash (e.g. ~3% under --> ~8% over)
        int nChains = getCollidingBuckets();
        long estimatedHeapUsageForChains = nChains * arrayHeapSize( 16 );
        memoryTracker.allocateHeap( estimatedHeapUsageForChains );
        trackedHeap += estimatedHeapUsageForChains;
    }

    @Override
    public void close()
    {
        memoryTracker.releaseHeap( SHALLOW_SIZE + trackedHeap );
    }

    static long arrayHeapSize( int arrayLength )
    {
        return alignObjectSize( ARRAY_HEADER_BYTES + (long) arrayLength * OBJECT_REFERENCE_BYTES );
    }
}