SimpleConcurrentMap.java

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package org.apache.wink.common.internal.utils;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * <p>
 * Concurrent implementation of the SimpleMap interface. The idea behind this
 * implementation that get is called more frequently than put or clear,
 * therefore ReentrantReadWriteLock is used: get is read operation, while put
 * and clear are write operations.
 * 
 * @param <K>
 * @param <V>
 * @see java.util.concurrent.locks.ReentrantReadWriteLock
 */
public class SimpleConcurrentMap<K, V> implements SimpleMap<K, V> {

    private final Lock      readersLock;
    private final Lock      writersLock;
    private final Map<K, V> map;

    public SimpleConcurrentMap() {
        this(new HashMap<K, V>());
    }

    /**
     * Provides the map implementation. Pay attention that get method is
     * synchronized using the read lock, therefore it must not change the
     * entire collection.
     * 
     * @param map
     */
    public SimpleConcurrentMap(Map<K, V> map) {
        this.map = map;
        ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        readersLock = readWriteLock.readLock();
        writersLock = readWriteLock.writeLock();
    }

    public V get(K key) {
        readersLock.lock();
        try {
            return map.get(key);
        } finally {
            readersLock.unlock();
        }
    }

    public V put(K key, V val) {
        writersLock.lock();
        try {
            return map.put(key, val);
        } finally {
            writersLock.unlock();
        }
    }

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