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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
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 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package jdk.nashorn.internal.runtime;

import java.lang.invoke.SwitchPoint;

This class represents a property map that can be shared among multiple prototype objects, allowing all inheriting top-level objects to also share one property map. This class is only used for prototype objects, the top-level objects use ordinary PropertyMaps with the PropertyMap.sharedProtoMap field set to the expected shared prototype map. 
When an instance of this class is evolved because a property is added, removed, or modified in an object using it, the invalidateSwitchPoint() method is invoked to signal to all callsites and inheriting objects that the assumption of a single shared prototype map is no longer valid. The property map resulting from the modification will no longer be an instance of this class.
/**
 * This class represents a property map that can be shared among multiple prototype objects, allowing all inheriting
 * top-level objects to also share one property map. This class is only used for prototype objects, the
 * top-level objects use ordinary {@link PropertyMap}s with the {@link PropertyMap#sharedProtoMap} field
 * set to the expected shared prototype map.
 *
 * <p>When an instance of this class is evolved because a property is added, removed, or modified in an object
 * using it, the {@link #invalidateSwitchPoint()} method is invoked to signal to all callsites and inheriting
 * objects that the assumption of a single shared prototype map is no longer valid. The property map resulting
 * from the modification will no longer be an instance of this class.</p>
 */
public final class SharedPropertyMap extends PropertyMap {

    private SwitchPoint switchPoint;

    private static final long serialVersionUID = 2166297719721778876L;

    
Create a new shared property map from the given map. 
Params:
map – property map to copy/**
     * Create a new shared property map from the given {@code map}.
     * @param map property map to copy
     */
    SharedPropertyMap(final PropertyMap map) {
        super(map);
        this.switchPoint = new SwitchPoint();
    }

    @Override
    public void propertyChanged(final Property property) {
        invalidateSwitchPoint();
        super.propertyChanged(property);
    }

    @Override
    synchronized boolean isValidSharedProtoMap() {
        return switchPoint != null;
    }

    @Override
    synchronized SwitchPoint getSharedProtoSwitchPoint() {
        return switchPoint;
    }

    
Invalidate the shared prototype switch point if this is a shared prototype map.
/**
     * Invalidate the shared prototype switch point if this is a shared prototype map.
     */
    synchronized void invalidateSwitchPoint() {
        if (switchPoint != null) {
            assert !switchPoint.hasBeenInvalidated();
            SwitchPoint.invalidateAll(new SwitchPoint[]{ switchPoint });
            switchPoint = null;
        }
    }
}