/*

 * 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.Map;

import java.util.Objects;

import java.util.function.BiConsumer;

import java.util.function.BiFunction;

import java.util.function.Function;

/**

 * A {@link java.util.Map} providing thread safety and atomicity

 * guarantees.

 *

 * <p>To maintain the specified guarantees, default implementations of

 * methods including {@link #putIfAbsent} inherited from {@link Map}

 * must be overridden by implementations of this interface. Similarly,

 * implementations of the collections returned by methods {@link

 * #keySet}, {@link #values}, and {@link #entrySet} must override

 * methods such as {@code removeIf} when necessary to

 * preserve atomicity guarantees.

 *

 * <p>Memory consistency effects: As with other concurrent

 * collections, actions in a thread prior to placing an object into a

 * {@code ConcurrentMap} as a key or value

 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>

 * actions subsequent to the access or removal of that object from

 * the {@code ConcurrentMap} in another thread.

 *

 * <p>This interface 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 interface ConcurrentMap<K,V> extends Map<K,V> {

    /**

     * {@inheritDoc}

     *

     * @implNote This implementation assumes that the ConcurrentMap cannot

     * contain null values and {@code get()} returning null unambiguously means

     * the key is absent. Implementations which support null values

     * <strong>must</strong> override this default implementation.

     *

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default V getOrDefault(Object key, V defaultValue) {

        V v;

        return ((v = get(key)) != null) ? v : defaultValue;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec The default implementation is equivalent to, for this

     * {@code map}:

     * <pre> {@code

     * for (Map.Entry<K,V> entry : map.entrySet()) {

     *   action.accept(entry.getKey(), entry.getValue());

     * }}</pre>

     *

     * @implNote The default implementation assumes that

     * {@code IllegalStateException} thrown by {@code getKey()} or

     * {@code getValue()} indicates that the entry has been removed and cannot

     * be processed. Operation continues for subsequent entries.

     *

     * @throws NullPointerException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default void forEach(BiConsumer<? super K, ? super V> action) {

        Objects.requireNonNull(action);

        for (Map.Entry<K,V> entry : entrySet()) {

            K k;

            V v;

            try {

                k = entry.getKey();

                v = entry.getValue();

            } catch (IllegalStateException ise) {

                // this usually means the entry is no longer in the map.

                continue;

            }

            action.accept(k, v);

        }

    }

    /**

     * If the specified key is not already associated

     * with a value, associates it with the given value.

     * This is equivalent to, for this {@code map}:

     * <pre> {@code

     * if (!map.containsKey(key))

     *   return map.put(key, value);

     * else

     *   return map.get(key);}</pre>

     *

     * except that the action is performed atomically.

     *

     * @implNote This implementation intentionally re-abstracts the

     * inappropriate default provided in {@code Map}.

     *

     * @param key key with which the specified value is to be associated

     * @param value value to be associated with the specified key

     * @return the previous value associated with the specified key, or

     *         {@code null} if there was no mapping for the key.

     *         (A {@code null} return can also indicate that the map

     *         previously associated {@code null} with the key,

     *         if the implementation supports null values.)

     * @throws UnsupportedOperationException if the {@code put} operation

     *         is not supported by this map

     * @throws ClassCastException if the class of the specified key or value

     *         prevents it from being stored in this map

     * @throws NullPointerException if the specified key or value is null,

     *         and this map does not permit null keys or values

     * @throws IllegalArgumentException if some property of the specified key

     *         or value prevents it from being stored in this map

     */

    V putIfAbsent(K key, V value);

    /**

     * Removes the entry for a key only if currently mapped to a given value.

     * This is equivalent to, for this {@code map}:

     * <pre> {@code

     * if (map.containsKey(key)

     *     && Objects.equals(map.get(key), value)) {

     *   map.remove(key);

     *   return true;

     * } else {

     *   return false;

     * }}</pre>

     *

     * except that the action is performed atomically.

     *

     * @implNote This implementation intentionally re-abstracts the

     * inappropriate default provided in {@code Map}.

     *

     * @param key key with which the specified value is associated

     * @param value value expected to be associated with the specified key

     * @return {@code true} if the value was removed

     * @throws UnsupportedOperationException if the {@code remove} operation

     *         is not supported by this map

     * @throws ClassCastException if the key or value is of an inappropriate

     *         type for this map

     * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)

     * @throws NullPointerException if the specified key or value is null,

     *         and this map does not permit null keys or values

     * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)

     */

    boolean remove(Object key, Object value);

    /**

     * Replaces the entry for a key only if currently mapped to a given value.

     * This is equivalent to, for this {@code map}:

     * <pre> {@code

     * if (map.containsKey(key)

     *     && Objects.equals(map.get(key), oldValue)) {

     *   map.put(key, newValue);

     *   return true;

     * } else {

     *   return false;

     * }}</pre>

     *

     * except that the action is performed atomically.

     *

     * @implNote This implementation intentionally re-abstracts the

     * inappropriate default provided in {@code Map}.

     *

     * @param key key with which the specified value is associated

     * @param oldValue value expected to be associated with the specified key

     * @param newValue value to be associated with the specified key

     * @return {@code true} if the value was replaced

     * @throws UnsupportedOperationException if the {@code put} operation

     *         is not supported by this map

     * @throws ClassCastException if the class of a specified key or value

     *         prevents it from being stored in this map

     * @throws NullPointerException if a specified key or value is null,

     *         and this map does not permit null keys or values

     * @throws IllegalArgumentException if some property of a specified key

     *         or value prevents it from being stored in this map

     */

    boolean replace(K key, V oldValue, V newValue);

    /**

     * Replaces the entry for a key only if currently mapped to some value.

     * This is equivalent to, for this {@code map}:

     * <pre> {@code

     * if (map.containsKey(key))

     *   return map.put(key, value);

     * else

     *   return null;}</pre>

     *

     * except that the action is performed atomically.

     *

     * @implNote This implementation intentionally re-abstracts the

     * inappropriate default provided in {@code Map}.

     *

     * @param key key with which the specified value is associated

     * @param value value to be associated with the specified key

     * @return the previous value associated with the specified key, or

     *         {@code null} if there was no mapping for the key.

     *         (A {@code null} return can also indicate that the map

     *         previously associated {@code null} with the key,

     *         if the implementation supports null values.)

     * @throws UnsupportedOperationException if the {@code put} operation

     *         is not supported by this map

     * @throws ClassCastException if the class of the specified key or value

     *         prevents it from being stored in this map

     * @throws NullPointerException if the specified key or value is null,

     *         and this map does not permit null keys or values

     * @throws IllegalArgumentException if some property of the specified key

     *         or value prevents it from being stored in this map

     */

    V replace(K key, V value);

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * <p>The default implementation is equivalent to, for this {@code map}:

     * <pre> {@code

     * for (Map.Entry<K,V> entry : map.entrySet()) {

     *   K k;

     *   V v;

     *   do {

     *     k = entry.getKey();

     *     v = entry.getValue();

     *   } while (!map.replace(k, v, function.apply(k, v)));

     * }}</pre>

     *

     * The default implementation may retry these steps when multiple

     * threads attempt updates including potentially calling the function

     * repeatedly for a given key.

     *

     * <p>This implementation assumes that the ConcurrentMap cannot contain null

     * values and {@code get()} returning null unambiguously means the key is

     * absent. Implementations which support null values <strong>must</strong>

     * override this default implementation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @throws ClassCastException {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {

        Objects.requireNonNull(function);

        forEach((k,v) -> {

            while (!replace(k, v, function.apply(k, v))) {

                // v changed or k is gone

                if ( (v = get(k)) == null) {

                    // k is no longer in the map.

                    break;

                }

            }

        });

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * The default implementation is equivalent to the following steps for this

     * {@code map}:

     *

     * <pre> {@code

     * V oldValue, newValue;

     * return ((oldValue = map.get(key)) == null

     *         && (newValue = mappingFunction.apply(key)) != null

     *         && (oldValue = map.putIfAbsent(key, newValue)) == null)

     *   ? newValue

     *   : oldValue;}</pre>

     *

     * <p>This implementation assumes that the ConcurrentMap cannot contain null

     * values and {@code get()} returning null unambiguously means the key is

     * absent. Implementations which support null values <strong>must</strong>

     * override this default implementation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default V computeIfAbsent(K key,

            Function<? super K, ? extends V> mappingFunction) {

        Objects.requireNonNull(mappingFunction);

        V oldValue, newValue;

        return ((oldValue = get(key)) == null

                && (newValue = mappingFunction.apply(key)) != null

                && (oldValue = putIfAbsent(key, newValue)) == null)

            ? newValue

            : oldValue;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * The default implementation is equivalent to performing the following

     * steps for this {@code map}:

     *

     * <pre> {@code

     * for (V oldValue; (oldValue = map.get(key)) != null; ) {

     *   V newValue = remappingFunction.apply(key, oldValue);

     *   if ((newValue == null)

     *       ? map.remove(key, oldValue)

     *       : map.replace(key, oldValue, newValue))

     *     return newValue;

     * }

     * return null;}</pre>

     * When multiple threads attempt updates, map operations and the

     * remapping function may be called multiple times.

     *

     * <p>This implementation assumes that the ConcurrentMap cannot contain null

     * values and {@code get()} returning null unambiguously means the key is

     * absent. Implementations which support null values <strong>must</strong>

     * override this default implementation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default V computeIfPresent(K key,

            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {

        Objects.requireNonNull(remappingFunction);

        for (V oldValue; (oldValue = get(key)) != null; ) {

            V newValue = remappingFunction.apply(key, oldValue);

            if ((newValue == null)

                ? remove(key, oldValue)

                : replace(key, oldValue, newValue))

                return newValue;

        }

        return null;

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * The default implementation is equivalent to performing the following

     * steps for this {@code map}:

     *

     * <pre> {@code

     * for (;;) {

     *   V oldValue = map.get(key);

     *   V newValue = remappingFunction.apply(key, oldValue);

     *   if (newValue != null) {

     *     if ((oldValue != null)

     *       ? map.replace(key, oldValue, newValue)

     *       : map.putIfAbsent(key, newValue) == null)

     *       return newValue;

     *   } else if (oldValue == null || map.remove(key, oldValue)) {

     *     return null;

     *   }

     * }}</pre>

     * When multiple threads attempt updates, map operations and the

     * remapping function may be called multiple times.

     *

     * <p>This implementation assumes that the ConcurrentMap cannot contain null

     * values and {@code get()} returning null unambiguously means the key is

     * absent. Implementations which support null values <strong>must</strong>

     * override this default implementation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default V compute(K key,

                      BiFunction<? super K, ? super V, ? extends V> remappingFunction) {

        retry: for (;;) {

            V oldValue = get(key);

            // if putIfAbsent fails, opportunistically use its return value

            haveOldValue: for (;;) {

                V newValue = remappingFunction.apply(key, oldValue);

                if (newValue != null) {

                    if (oldValue != null) {

                        if (replace(key, oldValue, newValue))

                            return newValue;

                    }

                    else if ((oldValue = putIfAbsent(key, newValue)) == null)

                        return newValue;

                    else continue haveOldValue;

                } else if (oldValue == null || remove(key, oldValue)) {

                    return null;

                }

                continue retry;

            }

        }

    }

    /**

     * {@inheritDoc}

     *

     * @implSpec

     * The default implementation is equivalent to performing the following

     * steps for this {@code map}:

     *

     * <pre> {@code

     * for (;;) {

     *   V oldValue = map.get(key);

     *   if (oldValue != null) {

     *     V newValue = remappingFunction.apply(oldValue, value);

     *     if (newValue != null) {

     *       if (map.replace(key, oldValue, newValue))

     *         return newValue;

     *     } else if (map.remove(key, oldValue)) {

     *       return null;

     *     }

     *   } else if (map.putIfAbsent(key, value) == null) {

     *     return value;

     *   }

     * }}</pre>

     * When multiple threads attempt updates, map operations and the

     * remapping function may be called multiple times.

     *

     * <p>This implementation assumes that the ConcurrentMap cannot contain null

     * values and {@code get()} returning null unambiguously means the key is

     * absent. Implementations which support null values <strong>must</strong>

     * override this default implementation.

     *

     * @throws UnsupportedOperationException {@inheritDoc}

     * @throws ClassCastException {@inheritDoc}

     * @throws NullPointerException {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     * @since 1.8

     */

    @Override

    default V merge(K key, V value,

            BiFunction<? super V, ? super V, ? extends V> remappingFunction) {

        Objects.requireNonNull(remappingFunction);

        Objects.requireNonNull(value);

        retry: for (;;) {

            V oldValue = get(key);

            // if putIfAbsent fails, opportunistically use its return value

            haveOldValue: for (;;) {

                if (oldValue != null) {

                    V newValue = remappingFunction.apply(oldValue, value);

                    if (newValue != null) {

                        if (replace(key, oldValue, newValue))

                            return newValue;

                    } else if (remove(key, oldValue)) {

                        return null;

                    }

                    continue retry;

                } else {

                    if ((oldValue = putIfAbsent(key, value)) == null)