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LongArrayHashMap.java
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LongArrayHashMap.java
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/*
* Copyright (c) 2002-2018 "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 <http://www.gnu.org/licenses/>.
*/
package org.neo4j.cypher.internal.runtime;
import org.opencypher.v9_0.util.InternalException;
import java.util.Iterator;
import java.util.Map;
import java.util.function.Supplier;
import org.neo4j.helpers.collection.Pair;
import org.neo4j.helpers.collection.PrefetchingIterator;
import static org.neo4j.cypher.internal.runtime.LongArrayHash.CONTINUE_PROBING;
import static org.neo4j.cypher.internal.runtime.LongArrayHash.NOT_IN_USE;
import static org.neo4j.cypher.internal.runtime.LongArrayHash.SLOT_EMPTY;
import static org.neo4j.cypher.internal.runtime.LongArrayHash.VALUE_FOUND;
/**
* A fast implementation of a hash map with long[] as keys.
*/
public class LongArrayHashMap<VALUE>
{
private final int keySize;
private LongArrayHashTable table;
private Object[] values;
public LongArrayHashMap( int initialCapacity, int keySize )
{
assert (initialCapacity & (initialCapacity - 1)) == 0 : "Capacity must be a power of 2";
assert keySize > 0 : "Number of elements must be larger than 0";
this.keySize = keySize;
table = new LongArrayHashTable( initialCapacity, keySize );
values = new Object[initialCapacity];
}
public VALUE computeIfAbsent( long[] key, Supplier<VALUE> creator )
{
assert LongArrayHash.validValue( key, keySize );
int slotNr = slotFor( key );
while ( true )
{
int currentState = table.checkSlot( slotNr, key );
switch ( currentState )
{
case SLOT_EMPTY:
if ( table.timeToResize() )
{
// We know we need to add the value to the set, but there is no space left
resize();
// Need to restart linear probe after resizing
slotNr = slotFor( key );
}
else
{
// We found an empty spot!
table.claimSlot( slotNr, key );
VALUE newValue = creator.get();
values[slotNr] = newValue;
return newValue;
}
break;
case CONTINUE_PROBING:
slotNr = (slotNr + 1) & table.tableMask;
break;
case VALUE_FOUND:
@SuppressWarnings( "unchecked" )
VALUE oldValue = (VALUE) values[slotNr];
return oldValue;
default:
throw new InternalException( "Unknown state returned from hash table " + currentState, null );
}
}
}
public VALUE get( long[] key )
{
assert LongArrayHash.validValue( key, keySize );
int slotNr = slotFor( key );
while ( true )
{
int currentState = table.checkSlot( slotNr, key );
switch ( currentState )
{
case SLOT_EMPTY:
return null;
case CONTINUE_PROBING:
slotNr = (slotNr + 1) & table.tableMask;
break;
case VALUE_FOUND:
@SuppressWarnings( "unchecked" )
VALUE oldValue = (VALUE) values[slotNr];
return oldValue;
default:
throw new InternalException( "Unknown state returned from hash table " + currentState, null );
}
}
}
public boolean isEmpty()
{
return table.isEmpty();
}
private void resize()
{
Pair<LongArrayHashTable,Object[]> resized = table.doubleCapacity( values );
table = resized.first();
values = resized.other();
}
private int slotFor( long[] value )
{
return LongArrayHash.hashCode( value, 0, keySize ) & table.tableMask;
}
public Iterator<Map.Entry<long[],VALUE>> iterator()
{
return new PrefetchingIterator<Map.Entry<long[],VALUE>>()
{
int current; // Initialized to 0
@Override
protected Map.Entry<long[],VALUE> fetchNextOrNull()
{
// First, find a good spot
while ( current < table.capacity && table.keys[current * keySize] == NOT_IN_USE )
{
current = current + 1;
}
// If we have reached the end, return null
if ( current == table.capacity )
{
return null;
}
// Otherwise, let's create the return object.
long[] key = new long[keySize];
System.arraycopy( table.keys, current * keySize, key, 0, keySize );
@SuppressWarnings( "unchecked" )
VALUE value = (VALUE) values[current];
Entry result = new Entry( key, value );
// Move
current = current + 1;
return result;
}
};
}
class Entry implements Map.Entry<long[],VALUE>
{
private final long[] key;
private final VALUE value;
Entry( long[] key, VALUE value )
{
this.key = key;
this.value = value;
}
@Override
public long[] getKey()
{
return key;
}
@Override
public VALUE getValue()
{
return value;
}
@Override
public VALUE setValue( VALUE value )
{
throw new UnsupportedOperationException();
}
}
}