org.eclipse.sisu.inject/src/org/eclipse/sisu/inject/MildConcurrentValues.java

/*******************************************************************************
 * Copyright (c) 2010, 2013 Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Stuart McCulloch (Sonatype, Inc.) - initial API and implementation
 *******************************************************************************/
package org.eclipse.sisu.inject;

import java.lang.ref.Reference;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;

/**
 * Thread-safe {@link Map} whose values are kept alive by soft/weak {@link Reference}s.
 */
final class MildConcurrentValues<K, V>
    extends MildValues<K, V>
    implements ConcurrentMap<K, V>
{
    // ----------------------------------------------------------------------
    // Implementation fields
    // ----------------------------------------------------------------------

    private final ConcurrentMap<K, Reference<V>> concurrentMap;

    // ----------------------------------------------------------------------
    // Constructors
    // ----------------------------------------------------------------------

    MildConcurrentValues( final ConcurrentMap<K, Reference<V>> map, final boolean soft )
    {
        super( map, soft );
        this.concurrentMap = map;
    }

    // ----------------------------------------------------------------------
    // Public methods
    // ----------------------------------------------------------------------

    public V putIfAbsent( final K key, final V value )
    {
        compact();

        final Reference<V> ref = mildValue( key, value );

        /*
         * We must either add our value to the map, or return a non-null existing value.
         */
        for ( Reference<V> oldRef; ( oldRef = concurrentMap.putIfAbsent( key, ref ) ) != null; )
        {
            final V oldValue = oldRef.get();
            if ( null != oldValue )
            {
                return oldValue;
            }
            concurrentMap.remove( key, oldRef ); // gone AWOL; remove entry and try again
        }
        return null;
    }

    public V replace( final K key, final V value )
    {
        compact();

        final Reference<V> ref = concurrentMap.replace( key, mildValue( key, value ) );
        return null != ref ? ref.get() : null;
    }

    public boolean replace( final K key, final V oldValue, final V newValue )
    {
        compact();

        return concurrentMap.replace( key, tempValue( oldValue ), mildValue( key, newValue ) );
    }

    public boolean remove( final Object key, final Object value )
    {
        compact(); // NOSONAR ignore nullable false-positive

        return concurrentMap.remove( key, tempValue( value ) );
    }

    // ----------------------------------------------------------------------
    // Implementation methods
    // ----------------------------------------------------------------------

    @Override
    void compact()
    {
        for ( Reference<? extends V> ref; ( ref = queue.poll() ) != null; )
        {
            // only remove this specific key-value mapping; thread-safe
            concurrentMap.remove( ( (InverseMapping) ref ).key(), ref );
        }
    }
}