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	/*
	* 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.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(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() {
	Cell[] as = cells; Cell a;
	long sum = base;
	if (as != null) {
	for (int i = 0; i < as.length; ++i) {
	if ((a = as[i]) != 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() {
	Cell[] as = cells; Cell a;
	base = 0L;
	if (as != null) {
	for (int i = 0; i < as.length; ++i) {
	if ((a = as[i]) != null)
	a.value = 0L;
	}
	}
	}

	/**
	* 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() {
	Cell[] as = cells; Cell a;
	long sum = base;
	base = 0L;
	if (as != null) {
	for (int i = 0; i < as.length; ++i) {
	if ((a = as[i]) != null) {
	sum += a.value;
	a.value = 0L;
	}
	}
	}
	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();
	}

	/**
	* Return a {@code LongAdder} object with initial state
	* held by this proxy.
	*
	* @return a {@code LongAdder} object with initial state
	* held by this proxy.
	*/
	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");
	}

	}

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