org.eclipse.persistence.internal.identitymaps.WeakIdentityMap Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of eclipselink Show documentation
EclipseLink build based upon Git transaction f2b9fc5
There is a newer version: 5.0.0-B03
/*
 * Copyright (c) 1998, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation from Oracle TopLink
package org.eclipse.persistence.internal.identitymaps;

import java.util.*;

import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.internal.sessions.AbstractSession;

/**
 * Purpose: A WeakIdentityMap holds all objects referenced by the application only.
 * The weak identity map is similar to the full identity map except for the fact that it allows
 * full garbage collection.
 * 
Responsibilities:

 *  Guarantees identity.
 * 
 Allows garbage collection.
 * 
 * @since TOPLink/Java 1.0
 */
public class WeakIdentityMap extends FullIdentityMap {

    /** Keep track of a counter to amortize cleanup of dead cache keys */
    protected volatile int cleanupCount;

    /** PERF: Keep track of a cleanup size to avoid cleanup bottleneck for large caches. */
    protected volatile int cleanupSize;

    public WeakIdentityMap(int size, ClassDescriptor descriptor, AbstractSession session, boolean isolated) {
        super(size, descriptor, session, isolated);
        this.cleanupCount = 0;
        this.cleanupSize = size;
    }

    /**
     * Search for any cache keys that have been garbage collected and remove them.
     * This must be done because although the objects held by the cache keys will garbage collect,
     * the keys themselves will not and must be cleaned up.  This is a linear operation so
     * is amortized through the cleanupCount to occur only once per cycle averaging to make
     * the total time still constant.
     */
    protected void cleanupDeadCacheKeys() {
        for (Iterator iterator = getCacheKeys().values().iterator(); iterator.hasNext();) {
            CacheKey key = (CacheKey)iterator.next();
            if (key.getObject() == null) {
                // Check lock first.
                // Change for CR 2317
                // Change for Bug 5840635 - use acquireIfUnownedNoWait()
                // Check lock first, only acquire if mutex's active thread is unset
                // as this thread could be entering a cache key that could be acquiring a lock
                // and we don't want to remove the cache key.
                if (key.acquireIfUnownedNoWait()) {
                    try {
                        if (key.getObject() == null) {
                            iterator.remove();
                        }
                    } finally {
                        key.release();
                    }
                }
            }
        }
    }

    @Override
    public CacheKey createCacheKey(Object primaryKey, Object object, Object writeLockValue, long readTime) {
        return new WeakCacheKey(primaryKey, object, writeLockValue, readTime, isIsolated);
    }

    /**
     * Need to check for cleanup on put.
     */
    @Override
    protected CacheKey putCacheKeyIfAbsent(CacheKey searchKey) {
        CacheKey cacheKey = super.putCacheKeyIfAbsent(searchKey);
        if (cacheKey == null) {
            checkCleanup();
        }
        return cacheKey;
    }

    /**
     * Check if garbage collected cache keys need to be cleaned up.
     */
    protected void checkCleanup() {
        // PERF: Avoid synchronization if cleanup not required (counts are volatile).
        if (this.cleanupCount > this.cleanupSize) {
            synchronized (this) {
                if (this.cleanupCount > this.cleanupSize) {
                    if ((this.session !=  null) && this.session.isConcurrent()) {
                        Runnable runnable = new Runnable() {
                            @Override
                            public void run() {
                                cleanupDeadCacheKeys();
                                WeakIdentityMap.this.cleanupCount = 0;
                                // PERF: Avoid cleanup bottleneck for large cache sizes, increase next cleanup.
                                int size = getSize();
                                if (size > WeakIdentityMap.this.cleanupSize) {
                                    WeakIdentityMap.this.cleanupSize = size;
                                }
                            }
                        };
                        this.session.getServerPlatform().launchContainerRunnable(runnable);
                    } else {
                        cleanupDeadCacheKeys();
                        this.cleanupCount = 0;
                        // PERF: Avoid cleanup bottleneck for large cache sizes, increase next cleanup.
                        int size = getSize();
                        if (size > this.cleanupSize) {
                            this.cleanupSize = size;
                        }
                    }
                }
            }
        }
        this.cleanupCount++;
    }
}