IdentityScopeObject.java

/*
 * Copyright (C) 2011 Markus Junginger, greenrobot (http://greenrobot.de)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package de.greenrobot.dao.identityscope;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.concurrent.locks.ReentrantLock;

/**
 * The context for entity identities. Provides the scope in which entities will be tracked and managed.
 * 
 * @author Markus
 * @param <K>
 * @param <T>
 */
public class IdentityScopeObject<K, T> implements IdentityScope<K, T> {
    private final HashMap<K, Reference<T>> map;
    private final ReentrantLock lock;

    public IdentityScopeObject() {
        map = new HashMap<K, Reference<T>>();
        lock = new ReentrantLock();
    }

    @Override
    public T get(K key) {
        Reference<T> ref;
        lock.lock();
        try {
            ref = map.get(key);
        } finally {
            lock.unlock();
        }
        if (ref != null) {
            return ref.get();
        } else {
            return null;
        }
    }

    @Override
    public T getNoLock(K key) {
        Reference<T> ref = map.get(key);
        if (ref != null) {
            return ref.get();
        } else {
            return null;
        }
    }

    @Override
    public void put(K key, T entity) {
        lock.lock();
        try {
            map.put(key, new WeakReference<T>(entity));
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void putNoLock(K key, T entity) {
        map.put(key, new WeakReference<T>(entity));
    }

    @Override
    public boolean detach(K key, T entity) {
        lock.lock();
        try {
            if (get(key) == entity && entity != null) {
                remove(key);
                return true;
            } else {
                return false;
            }
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void remove(K key) {
        lock.lock();
        try {
            map.remove(key);
        } finally {
            lock.unlock();
        }
    }
    
    @Override
    public void remove(Iterable< K> keys) {
        lock.lock();
        try {
            for (K key : keys) {
                map.remove(key);
            }
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void clear() {
        lock.lock();
        try {
            map.clear();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void lock() {
        lock.lock();
    }

    @Override
    public void unlock() {
        lock.unlock();
    }

    @Override
    public void reserveRoom(int count) {
        // HashMap does not allow
    }

}