/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Written by Doug Lea with assistance from members of JCP JSR-166

 * Expert Group and released to the public domain, as explained at

 * http://creativecommons.org/publicdomain/zero/1.0/

 */

package java.util.concurrent;

import java.util.*;

import java.io.Serializable;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

/**

 * A hash table supporting full concurrency of retrievals and adjustable

 * expected concurrency for updates. This class obeys the same functional

 * specification as {@link java.util.Hashtable}, and includes versions of

 * methods corresponding to each method of

 * <tt>Hashtable</tt>. However, even though all operations are thread-safe,

 * retrieval operations do <em>not</em> entail locking, and there is

 * <em>not</em> any support for locking the entire table in a way that prevents

 * all access. This class is fully interoperable with <tt>Hashtable</tt> in

 * programs that rely on its thread safety but not on its synchronization

 * details.

 *

 * <p>

 * Retrieval operations (including <tt>get</tt>) generally do not block, so may

 * overlap with update operations (including

 * <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results of the most

 * recently <em>completed</em> update operations holding upon their onset. For

 * aggregate operations such as <tt>putAll</tt>

 * and <tt>clear</tt>, concurrent retrievals may reflect insertion or removal of

 * only some entries. Similarly, Iterators and Enumerations return elements

 * reflecting the state of the hash table at some point at or since the creation

 * of the iterator/enumeration. They do <em>not</em> throw

 * {@link ConcurrentModificationException}. However, iterators are designed to

 * be used by only one thread at a time.

 *

 * <p>

 * The allowed concurrency among update operations is guided by the optional

 * <tt>concurrencyLevel</tt> constructor argument (default <tt>16</tt>), which

 * is used as a hint for internal sizing. The table is internally partitioned to

 * try to permit the indicated number of concurrent updates without contention.

 * Because placement in hash tables is essentially random, the actual

 * concurrency will vary. Ideally, you should choose a value to accommodate as

 * many threads as will ever concurrently modify the table. Using a

 * significantly higher value than you need can waste space and time, and a

 * significantly lower value can lead to thread contention. But overestimates

 * and underestimates within an order of magnitude do not usually have much

 * noticeable impact. A value of one is appropriate when it is known that only

 * one thread will modify and all others will only read. Also, resizing this or

 * any other kind of hash table is a relatively slow operation, so, when

 * possible, it is a good idea to provide estimates of expected table sizes in

 * constructors.

 *

 * <p>

 * This class and its views and iterators implement all of the

 * <em>optional</em> methods of the {@link Map} and {@link Iterator} interfaces.

 *

 * <p>

 * Like {@link Hashtable} but unlike {@link HashMap}, this class does

 * <em>not</em> allow <tt>null</tt> to be used as a key or value.

 *

 * <p>

 * This class is a member of the

 * <a href="{@docRoot}/../technotes/guides/collections/index.html">

 * Java Collections Framework</a>.

 *

 * @since 1.5

 * @author Doug Lea

 * @param <K> the type of keys maintained by this map

 * @param <V> the type of mapped values

 */

public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>

    implements ConcurrentMap<K, V>, Serializable {

    private static final long serialVersionUID = 7249069246763182397L;

    /**

     * The default initial capacity for this table,

     * used when not otherwise specified in a constructor.

     */

    static final int DEFAULT_INITIAL_CAPACITY = 16;

    /**

     * The default load factor for this table, used when not

     * otherwise specified in a constructor.

     */

    static final float DEFAULT_LOAD_FACTOR = 0.75f;

    /**

     * The default concurrency level for this table, used when not

     * otherwise specified in a constructor.

     */

    static final int DEFAULT_CONCURRENCY_LEVEL = 16;

    private final Map<K, V> delegate;

    /**

     * Creates a new, empty map with the specified initial

     * capacity, load factor and concurrency level.

     *

     * @param initialCapacity the initial capacity. The implementation

     * performs internal sizing to accommodate this many elements.

     * @param loadFactor  the load factor threshold, used to control resizing.

     * Resizing may be performed when the average number of elements per

     * bin exceeds this threshold.

     * @param concurrencyLevel the estimated number of concurrently

     * updating threads. The implementation performs internal sizing

     * to try to accommodate this many threads.

     * @throws IllegalArgumentException if the initial capacity is

     * negative or the load factor or concurrencyLevel are

     * nonpositive.

     */

    @SuppressWarnings("unchecked")

    public ConcurrentHashMap(int initialCapacity,

                             float loadFactor, int concurrencyLevel) {

        if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)

            throw new IllegalArgumentException();

        delegate = new HashMap<>(initialCapacity, loadFactor);

    }

    /**

     * Creates a new, empty map with the specified initial capacity

     * and load factor and with the default concurrencyLevel (16).

     *

     * @param initialCapacity The implementation performs internal

     * sizing to accommodate this many elements.

     * @param loadFactor  the load factor threshold, used to control resizing.

     * Resizing may be performed when the average number of elements per

     * bin exceeds this threshold.

     * @throws IllegalArgumentException if the initial capacity of

     * elements is negative or the load factor is nonpositive

     *

     * @since 1.6

     */

    public ConcurrentHashMap(int initialCapacity, float loadFactor) {

        this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);

    }

    /**

     * Creates a new, empty map with the specified initial capacity,

     * and with default load factor (0.75) and concurrencyLevel (16).

     *

     * @param initialCapacity the initial capacity. The implementation

     * performs internal sizing to accommodate this many elements.

     * @throws IllegalArgumentException if the initial capacity of

     * elements is negative.

     */

    public ConcurrentHashMap(int initialCapacity) {

        this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);

    }

    /**

     * Creates a new, empty map with a default initial capacity (16),

     * load factor (0.75) and concurrencyLevel (16).

     */

    public ConcurrentHashMap() {

        this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);

    }

    /**

     * Creates a new map with the same mappings as the given map.

     * The map is created with a capacity of 1.5 times the number

     * of mappings in the given map or 16 (whichever is greater),

     * and a default load factor (0.75) and concurrencyLevel (16).

     *

     * @param m the map

     */

    public ConcurrentHashMap(Map<? extends K, ? extends V> m) {

        this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,

                      DEFAULT_INITIAL_CAPACITY),

             DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);

        putAll(m);

    }

    @Override

    public int size() {

        return delegate.size();

    }

    @Override

    public boolean isEmpty() {

        return delegate.isEmpty();

    }

    @Override

    public boolean containsKey(Object key) {

        return delegate.containsKey(key);

    }

    @Override

    public boolean containsValue(Object value) {

        return delegate.containsValue(value);

    }

    @Override

    public V get(Object key) {

        return delegate.get(key);

    }

    @Override

    public V put(K key, V value) {

        return delegate.put(key, value);

    }

    @Override

    public V remove(Object key) {

        return delegate.remove(key);

    }

    @Override

    public void putAll(Map<? extends K, ? extends V> m) {

        delegate.putAll(m);

    }

    @Override

    public void clear() {

        delegate.clear();

    }

    @Override

    public Set<K> keySet() {

        return delegate.keySet();

    }

    @Override

    public Collection<V> values() {

        return delegate.values();

    }

    @Override

    public Set<Entry<K, V>> entrySet() {

        return delegate.entrySet();

    }

    @Override

    public boolean equals(Object o) {

        return delegate.equals(o);

    }

    @Override

    public int hashCode() {

        return delegate.hashCode();

    }

    @Override

    public String toString() {

        return delegate.toString();

    }

    @Override

    public V putIfAbsent(K key, V value) {

        V old = delegate.get(key);

        if (old == null) {

            return delegate.put(key, value);

        }

        return old;

    }

    @Override

    public boolean remove(Object key, Object value) {

        if (equals(value, delegate.get(key))) {

            delegate.remove(key);

            return true;

        } else {

            return false;

        }

    }

    @Override

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

        if (equals(oldValue, delegate.get(key))) {

            delegate.put(key, newValue);

            return true;

        } else {

            return false;

        }

    }

    @Override

    public V replace(K key, V value) {

        if (delegate.containsKey(key)) {

            return delegate.put(key, value);

        } else {

            return null;

        }

    }

    private static boolean equals(Object a, Object b) {

        if (a == null) {

            return b == null;

        } else {

            return a.equals(b);

        }

    }

}