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fastutil extends the Java Collections Framework by providing type-specific maps, sets, lists and priority queues with a small memory footprint and fast access and insertion; provides also big (64-bit) arrays, sets and lists, and fast, practical I/O classes for binary and text files.
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/*
 * Copyright (C) 2002-2017 Sebastiano Vigna
 *
 * 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 PACKAGE;

import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;

import java.io.Serializable;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

/** A concurrent counting map. The map is made by a number of stripes (instances of {@link Object2IntOpenHashMap})
 * which are accessed independently
 * using a {@link ReentrantReadWriteLock}. Only one thread can write in a stripe at a time, but different stripes
 * can be modified independently and read access can happen concurrently on each stripe.
 *
 * @param  the type of keys.
 */

public class STRIPED_OPEN_HASH_MAP KEY_VALUE_GENERIC extends ABSTRACT_MAP KEY_VALUE_GENERIC implements java.io.Serializable, Cloneable {
	private static final long serialVersionUID = 1L;

	/** The stripes. Keys are distributed among them using the lower bits of their {@link Object#hashCode()}. */
	private final OPEN_HASH_MAP KEY_VALUE_GENERIC[] map;
	/** An array of locks parallel to {@link #map}, protecting each stripe. */
	private final transient ReentrantReadWriteLock[] lock;
	/** {@link #map map.length} − 1, cached. */
	private final int mask;

	/** Creates a new concurrent counting map with concurrency level equal to {@link Runtime#availableProcessors()}. */
	public STRIPED_OPEN_HASH_MAP() {
		this(Runtime.getRuntime().availableProcessors());
	}

	/** Creates a new concurrent counting map.
	 *
	 * @param concurrencyLevel the number of stripes (it will be {@linkplain Integer#highestOneBit(int) forced to be a power of two}); ideally, as large as the number of threads that will ever access
	 * this map, but higher values require more space.
	 */
	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public STRIPED_OPEN_HASH_MAP(final int concurrencyLevel) {
		map = new OPEN_HASH_MAP[Integer.highestOneBit(concurrencyLevel)];
		lock = new ReentrantReadWriteLock[map.length];
		for(int i = map.length; i-- != 0;) {
			map[i] = new OPEN_HASH_MAP KEY_VALUE_GENERIC();
			lock[i] = new ReentrantReadWriteLock();
		}
		mask = map.length - 1;
	}

#if KEYS_PRIMITIVE

	public VALUE_GENERIC_CLASS get(final KEY_CLASS k) {
		final int stripe = KEY2INTHASH(k) & mask;
		final ReadLock readLock = lock[stripe].readLock();
		try {
			readLock.lock();
			return map[stripe].get(k);
		}
		finally {
			readLock.unlock();
		}
	}

#endif

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public VALUE_GENERIC_TYPE GET_VALUE(final KEY_TYPE k) {
		final int stripe = KEY2INTHASH(k) & mask;
		final ReadLock readLock = lock[stripe].readLock();
		try {
			readLock.lock();
			return map[stripe].GET_VALUE(k);
		}
		finally {
			readLock.unlock();
		}
	}

	public VALUE_GENERIC_TYPE put(final KEY_GENERIC_TYPE k, final VALUE_GENERIC_TYPE v) {
		final int stripe = KEY2INTHASH(k) & mask;
		final WriteLock writeLock = lock[stripe].writeLock();
		try {
			writeLock.lock();
			return map[stripe].put(k, v);
		}
		finally {
			writeLock.unlock();
		}
	}

	public VALUE_GENERIC_TYPE putIfAbsent(final KEY_GENERIC_TYPE k, final VALUE_GENERIC_TYPE v) {
		final int stripe = KEY2INTHASH(k) & mask;
		final WriteLock writeLock = lock[stripe].writeLock();
		try {
			writeLock.lock();
			if (map[stripe].containsKey(k)) return map[stripe].get(k);
			return map[stripe].put(k, v);
		}
		finally {
			writeLock.unlock();
		}
	}

#if VALUES_PRIMITIVE || KEYS_PRIMITIVE

	public VALUE_GENERIC_CLASS put(final KEY_GENERIC_CLASS ok, final VALUE_GENERIC_CLASS ov) {
		final int stripe = KEY2INTHASH(ok) & mask;
		final WriteLock writeLock = lock[stripe].writeLock();
		try {
			writeLock.lock();
			return map[stripe].put(ok, ov);
		}
		finally {
			writeLock.unlock();
		}
	}


	public VALUE_GENERIC_CLASS putIfAbsent(final KEY_GENERIC_CLASS ok, final VALUE_GENERIC_CLASS ov) {
		final int stripe = KEY2INTHASH(ok) & mask;
		final WriteLock writeLock = lock[stripe].writeLock();
		try {
			writeLock.lock();
			if (map[stripe].containsKey(ok)) return map[stripe].get(ok);
			return map[stripe].put(ok, ov);
		}
		finally {
			writeLock.unlock();
		}
	}

#endif

	public int size() {
		int size = 0;
		for(int stripe = lock.length; stripe-- != 0;) {
			final ReadLock readLock = lock[stripe].readLock();
			try {
				readLock.lock();
				size += map[stripe].size();
			}
			finally {
				readLock.unlock();
			}
		}

		return size;
	}

	public FastEntrySet KEY_VALUE_GENERIC ENTRYSET() {
		throw new UnsupportedOperationException();
	}
}