| /* |
| * 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 static java.lang.Double.doubleToRawLongBits; |
| import static java.lang.Double.longBitsToDouble; |
| |
| import java.io.Serializable; |
| import java.util.function.DoubleBinaryOperator; |
| |
| /** |
| * One or more variables that together maintain a running {@code double} |
| * 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 #doubleValue}) returns the current value |
| * across the variables maintaining updates. |
| * |
| * <p>This class is usually preferable to alternatives when multiple |
| * threads update a common value that is used for purposes such as |
| * summary statistics that are frequently updated but less frequently |
| * read. |
| * |
| * <p>The supplied accumulator function should be side-effect-free, |
| * since it may be re-applied when attempted updates fail due to |
| * contention among threads. For predictable results, the accumulator |
| * function should be commutative and associative within the floating |
| * point tolerance required in usage contexts. The function is applied |
| * with an existing value (or identity) as one argument, and a given |
| * update as the other argument. For example, to maintain a running |
| * maximum value, you could supply {@code Double::max} along with |
| * {@code Double.NEGATIVE_INFINITY} as the identity. The order of |
| * accumulation within or across threads is not guaranteed. Thus, this |
| * class may not be applicable if numerical stability is required, |
| * especially when combining values of substantially different orders |
| * of magnitude. |
| * |
| * <p>Class {@link DoubleAdder} provides analogs of the functionality |
| * of this class for the common special case of maintaining sums. The |
| * call {@code new DoubleAdder()} is equivalent to {@code new |
| * DoubleAccumulator((x, y) -> x + y, 0.0)}. |
| * |
| * <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 DoubleAccumulator extends Striped64 implements Serializable { |
| private static final long serialVersionUID = 7249069246863182397L; |
| |
| private final DoubleBinaryOperator function; |
| private final long identity; // use long representation |
| |
| /** |
| * 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 DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, |
| double identity) { |
| this.function = accumulatorFunction; |
| base = this.identity = doubleToRawLongBits(identity); |
| } |
| |
| /** |
| * Updates with the given value. |
| * |
| * @param x the value |
| */ |
| public void accumulate(double x) { |
| Cell[] as; long b, v, r; int m; Cell a; |
| if ((as = cells) != null |
| || ((r = doubleToRawLongBits |
| (function.applyAsDouble(longBitsToDouble(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 = doubleToRawLongBits |
| (function.applyAsDouble |
| (longBitsToDouble(v = a.value), x))) == v) |
| || a.cas(v, r))) |
| doubleAccumulate(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 double get() { |
| Cell[] as = cells; |
| double result = longBitsToDouble(base); |
| if (as != null) { |
| for (Cell a : as) |
| if (a != null) |
| result = function.applyAsDouble |
| (result, longBitsToDouble(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 double getThenReset() { |
| Cell[] as = cells; |
| double result = longBitsToDouble(base); |
| base = identity; |
| if (as != null) { |
| for (Cell a : as) { |
| if (a != null) { |
| double v = longBitsToDouble(a.value); |
| a.reset(identity); |
| result = function.applyAsDouble(result, v); |
| } |
| } |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the String representation of the current value. |
| * @return the String representation of the current value |
| */ |
| public String toString() { |
| return Double.toString(get()); |
| } |
| |
| /** |
| * Equivalent to {@link #get}. |
| * |
| * @return the current value |
| */ |
| public double doubleValue() { |
| return get(); |
| } |
| |
| /** |
| * Returns the {@linkplain #get current value} as a {@code long} |
| * after a narrowing primitive conversion. |
| */ |
| public long longValue() { |
| return (long)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 narrowing primitive conversion. |
| */ |
| public float floatValue() { |
| return (float)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 double value; |
| |
| /** |
| * The function used for updates. |
| * @serial |
| */ |
| private final DoubleBinaryOperator function; |
| |
| /** |
| * The identity value, represented as a long, as converted by |
| * {@link Double#doubleToRawLongBits}. The original identity |
| * can be recovered using {@link Double#longBitsToDouble}. |
| * @serial |
| */ |
| private final long identity; |
| |
| SerializationProxy(double value, |
| DoubleBinaryOperator function, |
| long identity) { |
| this.value = value; |
| this.function = function; |
| this.identity = identity; |
| } |
| |
| /** |
| * Returns a {@code DoubleAccumulator} object with initial state |
| * held by this proxy. |
| * |
| * @return a {@code DoubleAccumulator} object with initial state |
| * held by this proxy |
| */ |
| private Object readResolve() { |
| double d = longBitsToDouble(identity); |
| DoubleAccumulator a = new DoubleAccumulator(function, d); |
| a.base = doubleToRawLongBits(value); |
| return a; |
| } |
| } |
| |
| /** |
| * Returns a |
| * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAccumulator.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"); |
| } |
| |
| } |