/*

 * 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

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 */

/*

 * 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.atomic;

import java.io.Serializable;

/**

 * One or more variables that together maintain an initially zero

 * {@code long} sum.  When updates (method {@link #add}) are contended

 * across threads, the set of variables may grow dynamically to reduce

 * contention. Method {@link #sum} (or, equivalently, {@link

 * #longValue}) returns the current total combined across the

 * variables maintaining the sum.

 *

 * <p>This class is usually preferable to {@link AtomicLong} when

 * multiple threads update a common sum that is used for purposes such

 * as collecting statistics, not for fine-grained synchronization

 * control.  Under low update contention, the two classes have similar

 * characteristics. But under high contention, expected throughput of

 * this class is significantly higher, at the expense of higher space

 * consumption.

 *

 * <p>LongAdders can be used with a {@link

 * java.util.concurrent.ConcurrentHashMap} to maintain a scalable

 * frequency map (a form of histogram or multiset). For example, to

 * add a count to a {@code ConcurrentHashMap<String,LongAdder> freqs},

 * initializing if not already present, you can use {@code

 * freqs.computeIfAbsent(key, k -> new LongAdder()).increment();}

 *

 * <p>This class extends {@link Number}, but does <em>not</em> define

 * methods such as {@code equals}, {@code hashCode} and {@code

 * compareTo} because instances are expected to be mutated, and so are

 * not useful as collection keys.

 *

 * @since 1.8

 * @author Doug Lea

 */

public class LongAdder extends Striped64 implements Serializable {

    private static final long serialVersionUID = 7249069246863182397L;

    /**

     * Creates a new adder with initial sum of zero.

     */

    public LongAdder() {

    }

    /**

     * Adds the given value.

     *

     * @param x the value to add

     */

    public void add(long x) {

        Cell[] as; long b, v; int m; Cell a;

        if ((as = cells) != null || !casBase(b = base, b + x)) {

            boolean uncontended = true;

            if (as == null || (m = as.length - 1) < 0 ||

                (a = as[getProbe() & m]) == null ||

                !(uncontended = a.cas(v = a.value, v + x)))

                longAccumulate(x, null, uncontended);

        }

    }

    /**

     * Equivalent to {@code add(1)}.

     */

    public void increment() {

        add(1L);

    }

    /**

     * Equivalent to {@code add(-1)}.

     */

    public void decrement() {

        add(-1L);

    }

    /**

     * Returns the current sum.  The returned value is <em>NOT</em> an

     * atomic snapshot; invocation in the absence of concurrent

     * updates returns an accurate result, but concurrent updates that

     * occur while the sum is being calculated might not be

     * incorporated.

     *

     * @return the sum

     */

    public long sum() {

        long sum = base;

        if (as != null) {

                    sum += a.value;

        }

        return sum;

    }

    /**

     * Resets variables maintaining the sum to zero.  This method may

     * be a useful alternative to creating a new adder, but is only

     * effective if there are no concurrent updates.  Because this

     * method is intrinsically racy, it should only be used when it is

     * known that no threads are concurrently updating.

     */

    public void reset() {

        base = 0L;

        if (as != null) {

        }

    }

    /**

     * Equivalent in effect to {@link #sum} followed by {@link

     * #reset}. This method may apply for example during quiescent

     * points between multithreaded computations.  If there are

     * updates concurrent with this method, the returned value is

     * <em>not</em> guaranteed to be the final value occurring before

     * the reset.

     *

     * @return the sum

     */

    public long sumThenReset() {

        long sum = base;

        base = 0L;

        if (as != null) {

                    sum += a.value;

                }

            }

        }

        return sum;

    }

    /**

     * Returns the String representation of the {@link #sum}.

     * @return the String representation of the {@link #sum}

     */

    public String toString() {

        return Long.toString(sum());

    }

    /**

     * Equivalent to {@link #sum}.

     *

     * @return the sum

     */

    public long longValue() {

        return sum();

    }

    /**

     * Returns the {@link #sum} as an {@code int} after a narrowing

     * primitive conversion.

     */

    public int intValue() {

        return (int)sum();

    }

    /**

     * Returns the {@link #sum} as a {@code float}

     * after a widening primitive conversion.

     */

    public float floatValue() {

        return (float)sum();

    }

    /**

     * Returns the {@link #sum} as a {@code double} after a widening

     * primitive conversion.

     */

    public double doubleValue() {

        return (double)sum();

    }

    /**

     * Serialization proxy, used to avoid reference to the non-public

     * Striped64 superclass in serialized forms.

     * @serial include

     */

    private static class SerializationProxy implements Serializable {

        private static final long serialVersionUID = 7249069246863182397L;

        /**

         * The current value returned by sum().

         * @serial

         */

        private final long value;

        SerializationProxy(LongAdder a) {

            value = a.sum();

        }

        /**

         * held by this proxy.

         *

         * @return a {@code LongAdder} object with initial state

         */

        private Object readResolve() {

            LongAdder a = new LongAdder();

            a.base = value;

            return a;

        }

    }

    /**

     * Returns a

     * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.LongAdder.SerializationProxy">

     * SerializationProxy</a>

     * representing the state of this instance.

     *

     * @return a {@link SerializationProxy}

     * representing the state of this instance

     */

    private Object writeReplace() {

        return new SerializationProxy(this);

    }

    /**

     * @param s the stream

     * @throws java.io.InvalidObjectException always

     */

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.InvalidObjectException {

        throw new java.io.InvalidObjectException("Proxy required");

    }

}