--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/atomic/LongAccumulator.java Mon Jan 21 13:50:05 2013 +0000
@@ -0,0 +1,236 @@
+/*
+ * 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.
+ */
+ 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.operateAsLong(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.operateAsLong(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; Cell a;
+ long result = base;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null)
+ result = function.operateAsLong(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; Cell a;
+ base = identity;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null)
+ a.value = 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; Cell a;
+ long result = base;
+ base = identity;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null) {
+ long v = a.value;
+ a.value = identity;
+ result = function.operateAsLong(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();
+ }
+
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ s.defaultWriteObject();
+ s.writeLong(get());
+ }
+
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+ cellsBusy = 0;
+ cells = null;
+ base = s.readLong();
+ }
+
+}