--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/atomic/LongAdder.java Mon Jan 21 13:50:05 2013 +0000
@@ -0,0 +1,228 @@
+/*
+ * 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 long} 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
+ * #longValue}) returns the current total combined across the
+ * variables maintaining the sum.
+ *
+ * <p>This class is usually preferable to {@link AtomicLong} when
+ * multiple threads update a common sum 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>LongAdders can be used with a {@link
+ * java.util.concurrent.ConcurrentHashMap} to maintain a scalable
+ * frequency map (a form of histogram or multiset). For example, to
+ * add a count to a {@code ConcurrentHashMap<String,LongAdder> freqs},
+ * initializing if not already present, you can use {@code
+ * freqs.computeIfAbsent(k -> new LongAdder()).increment();}
+ *
+ * <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 LongAdder extends Striped64 implements Serializable {
+ private static final long serialVersionUID = 7249069246863182397L;
+
+ /**
+ * Creates a new adder with initial sum of zero.
+ */
+ public LongAdder() {
+ }
+
+ /**
+ * Adds the given value.
+ *
+ * @param x the value to add
+ */
+ public void add(long x) {
+ Cell[] as; long b, v; int m; Cell a;
+ if ((as = cells) != null || !casBase(b = base, b + x)) {
+ boolean uncontended = true;
+ if (as == null || (m = as.length - 1) < 0 ||
+ (a = as[getProbe() & m]) == null ||
+ !(uncontended = a.cas(v = a.value, v + x)))
+ longAccumulate(x, null, uncontended);
+ }
+ }
+
+ /**
+ * Equivalent to {@code add(1)}.
+ */
+ public void increment() {
+ add(1L);
+ }
+
+ /**
+ * Equivalent to {@code add(-1)}.
+ */
+ public void decrement() {
+ add(-1L);
+ }
+
+ /**
+ * 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.
+ *
+ * @return the sum
+ */
+ public long sum() {
+ Cell[] as = cells; Cell a;
+ long sum = base;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null)
+ sum += 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; Cell a;
+ base = 0L;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null)
+ a.value = 0L;
+ }
+ }
+ }
+
+ /**
+ * 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 long sumThenReset() {
+ Cell[] as = cells; Cell a;
+ long sum = base;
+ base = 0L;
+ if (as != null) {
+ for (int i = 0; i < as.length; ++i) {
+ if ((a = as[i]) != null) {
+ sum += a.value;
+ a.value = 0L;
+ }
+ }
+ }
+ return sum;
+ }
+
+ /**
+ * Returns the String representation of the {@link #sum}.
+ * @return the String representation of the {@link #sum}
+ */
+ public String toString() {
+ return Long.toString(sum());
+ }
+
+ /**
+ * Equivalent to {@link #sum}.
+ *
+ * @return the sum
+ */
+ public long longValue() {
+ return 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 widening primitive conversion.
+ */
+ public float floatValue() {
+ return (float)sum();
+ }
+
+ /**
+ * Returns the {@link #sum} as a {@code double} after a widening
+ * primitive conversion.
+ */
+ public double doubleValue() {
+ return (double)sum();
+ }
+
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ s.defaultWriteObject();
+ s.writeLong(sum());
+ }
+
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+ cellsBusy = 0;
+ cells = null;
+ base = s.readLong();
+ }
+
+}