| /* |
| * 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 double} 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 |
| * #doubleValue}) returns the current total combined across the |
| * variables maintaining the sum. 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>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>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 DoubleAdder extends Striped64 implements Serializable { |
| private static final long serialVersionUID = 7249069246863182397L; |
| |
| /* |
| * Note that we must use "long" for underlying representations, |
| * because there is no compareAndSet for double, due to the fact |
| * that the bitwise equals used in any CAS implementation is not |
| * the same as double-precision equals. However, we use CAS only |
| * to detect and alleviate contention, for which bitwise equals |
| * works best anyway. In principle, the long/double conversions |
| * used here should be essentially free on most platforms since |
| * they just re-interpret bits. |
| */ |
| |
| /** |
| * Creates a new adder with initial sum of zero. |
| */ |
| public DoubleAdder() { |
| } |
| |
| /** |
| * Adds the given value. |
| * |
| * @param x the value to add |
| */ |
| public void add(double x) { |
| Cell[] as; long b, v; int m; Cell a; |
| if ((as = cells) != null || |
| !casBase(b = base, |
| Double.doubleToRawLongBits |
| (Double.longBitsToDouble(b) + x))) { |
| boolean uncontended = true; |
| if (as == null || (m = as.length - 1) < 0 || |
| (a = as[getProbe() & m]) == null || |
| !(uncontended = a.cas(v = a.value, |
| Double.doubleToRawLongBits |
| (Double.longBitsToDouble(v) + x)))) |
| doubleAccumulate(x, null, uncontended); |
| } |
| } |
| |
| /** |
| * 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. Also, because floating-point arithmetic is not |
| * strictly associative, the returned result need not be identical |
| * to the value that would be obtained in a sequential series of |
| * updates to a single variable. |
| * |
| * @return the sum |
| */ |
| public double sum() { |
| Cell[] as = cells; |
| double sum = Double.longBitsToDouble(base); |
| if (as != null) { |
| for (Cell a : as) |
| if (a != null) |
| sum += Double.longBitsToDouble(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; |
| base = 0L; // relies on fact that double 0 must have same rep as long |
| if (as != null) { |
| for (Cell a : as) |
| if (a != null) |
| a.reset(); |
| } |
| } |
| |
| /** |
| * 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 double sumThenReset() { |
| Cell[] as = cells; |
| double sum = Double.longBitsToDouble(base); |
| base = 0L; |
| if (as != null) { |
| for (Cell a : as) { |
| if (a != null) { |
| long v = a.value; |
| a.reset(); |
| sum += Double.longBitsToDouble(v); |
| } |
| } |
| } |
| return sum; |
| } |
| |
| /** |
| * Returns the String representation of the {@link #sum}. |
| * @return the String representation of the {@link #sum} |
| */ |
| public String toString() { |
| return Double.toString(sum()); |
| } |
| |
| /** |
| * Equivalent to {@link #sum}. |
| * |
| * @return the sum |
| */ |
| public double doubleValue() { |
| return sum(); |
| } |
| |
| /** |
| * Returns the {@link #sum} as a {@code long} after a |
| * narrowing primitive conversion. |
| */ |
| public long longValue() { |
| return (long)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 narrowing primitive conversion. |
| */ |
| public float floatValue() { |
| return (float)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 double value; |
| |
| SerializationProxy(DoubleAdder a) { |
| value = a.sum(); |
| } |
| |
| /** |
| * Returns a {@code DoubleAdder} object with initial state |
| * held by this proxy. |
| * |
| * @return a {@code DoubleAdder} object with initial state |
| * held by this proxy |
| */ |
| private Object readResolve() { |
| DoubleAdder a = new DoubleAdder(); |
| a.base = Double.doubleToRawLongBits(value); |
| return a; |
| } |
| } |
| |
| /** |
| * Returns a |
| * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAdder.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"); |
| } |
| |
| } |