| /* |
| * 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; |
| import java.util.function.LongBinaryOperator; |
| |
| /** |
| * One or more variables that together maintain a running {@code long} |
| * value updated using a supplied function. When updates (method |
| * {@link #accumulate}) are contended across threads, the set of variables |
| * may grow dynamically to reduce contention. Method {@link #get} |
| * (or, equivalently, {@link #longValue}) returns the current value |
| * across the variables maintaining updates. |
| * |
| * <p>This class is usually preferable to {@link AtomicLong} when |
| * multiple threads update a common value 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>The order of accumulation within or across threads is not |
| * guaranteed and cannot be depended upon, so this class is only |
| * applicable to functions for which the order of accumulation does |
| * not matter. The supplied accumulator function should be |
| * side-effect-free, since it may be re-applied when attempted updates |
| * fail due to contention among threads. The function is applied with |
| * the current value as its first argument, and the given update as |
| * the second argument. For example, to maintain a running maximum |
| * value, you could supply {@code Long::max} along with {@code |
| * Long.MIN_VALUE} as the identity. |
| * |
| * <p>Class {@link LongAdder} provides analogs of the functionality of |
| * this class for the common special case of maintaining counts and |
| * sums. The call {@code new LongAdder()} is equivalent to {@code new |
| * LongAccumulator((x, y) -> x + y, 0L)}. |
| * |
| * <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 LongAccumulator extends Striped64 implements Serializable { |
| private static final long serialVersionUID = 7249069246863182397L; |
| |
| private final LongBinaryOperator function; |
| private final long identity; |
| |
| /** |
| * Creates a new instance using the given accumulator function |
| * and identity element. |
| * @param accumulatorFunction a side-effect-free function of two arguments |
| * @param identity identity (initial value) for the accumulator function |
| */ |
| public LongAccumulator(LongBinaryOperator accumulatorFunction, |
| long identity) { |
| this.function = accumulatorFunction; |
| base = this.identity = identity; |
| } |
| |
| /** |
| * Updates with the given value. |
| * |
| * @param x the value |
| */ |
| public void accumulate(long x) { |
| Cell[] as; long b, v, r; int m; Cell a; |
| if ((as = cells) != null |
| || ((r = function.applyAsLong(b = base, x)) != b |
| && !casBase(b, r))) { |
| boolean uncontended = true; |
| if (as == null |
| || (m = as.length - 1) < 0 |
| || (a = as[getProbe() & m]) == null |
| || !(uncontended = |
| (r = function.applyAsLong(v = a.value, x)) == v |
| || a.cas(v, r))) |
| longAccumulate(x, function, uncontended); |
| } |
| } |
| |
| /** |
| * Returns the current value. 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 value is being calculated might not be |
| * incorporated. |
| * |
| * @return the current value |
| */ |
| public long get() { |
| Cell[] as = cells; |
| long result = base; |
| if (as != null) { |
| for (Cell a : as) |
| if (a != null) |
| result = function.applyAsLong(result, a.value); |
| } |
| return result; |
| } |
| |
| /** |
| * Resets variables maintaining updates to the identity value. |
| * This method may be a useful alternative to creating a new |
| * updater, 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; |
| base = identity; |
| if (as != null) { |
| for (Cell a : as) |
| if (a != null) |
| a.reset(identity); |
| } |
| } |
| |
| /** |
| * Equivalent in effect to {@link #get} 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 value before reset |
| */ |
| public long getThenReset() { |
| Cell[] as = cells; |
| long result = base; |
| base = identity; |
| if (as != null) { |
| for (Cell a : as) { |
| if (a != null) { |
| long v = a.value; |
| a.reset(identity); |
| result = function.applyAsLong(result, v); |
| } |
| } |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the String representation of the current value. |
| * @return the String representation of the current value |
| */ |
| public String toString() { |
| return Long.toString(get()); |
| } |
| |
| /** |
| * Equivalent to {@link #get}. |
| * |
| * @return the current value |
| */ |
| public long longValue() { |
| return get(); |
| } |
| |
| /** |
| * Returns the {@linkplain #get current value} as an {@code int} |
| * after a narrowing primitive conversion. |
| */ |
| public int intValue() { |
| return (int)get(); |
| } |
| |
| /** |
| * Returns the {@linkplain #get current value} as a {@code float} |
| * after a widening primitive conversion. |
| */ |
| public float floatValue() { |
| return (float)get(); |
| } |
| |
| /** |
| * Returns the {@linkplain #get current value} as a {@code double} |
| * after a widening primitive conversion. |
| */ |
| public double doubleValue() { |
| return (double)get(); |
| } |
| |
| /** |
| * 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 get(). |
| * @serial |
| */ |
| private final long value; |
| |
| /** |
| * The function used for updates. |
| * @serial |
| */ |
| private final LongBinaryOperator function; |
| |
| /** |
| * The identity value. |
| * @serial |
| */ |
| private final long identity; |
| |
| SerializationProxy(long value, |
| LongBinaryOperator function, |
| long identity) { |
| this.value = value; |
| this.function = function; |
| this.identity = identity; |
| } |
| |
| /** |
| * Returns a {@code LongAccumulator} object with initial state |
| * held by this proxy. |
| * |
| * @return a {@code LongAccumulator} object with initial state |
| * held by this proxy |
| */ |
| private Object readResolve() { |
| LongAccumulator a = new LongAccumulator(function, identity); |
| a.base = value; |
| return a; |
| } |
| } |
| |
| /** |
| * Returns a |
| * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.LongAccumulator.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(get(), function, identity); |
| } |
| |
| /** |
| * @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"); |
| } |
| |
| } |