--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/concurrent/atomic/DoubleAccumulator.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,305 @@
+/*
+ * 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");
+ }
+
+}