All Downloads are FREE. Search and download functionalities are using the official Maven repository.

com.google.common.cache.LongAdder Maven / Gradle / Ivy

Go to download

Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.

There is a newer version: 33.3.0-jre
Show newest version
/*
 * 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/
 */

/*
 * Source:
 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/LongAdder.java?revision=1.8
 */

package com.google.common.cache;

import com.google.common.annotations.GwtCompatible;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.concurrent.atomic.AtomicLong;

/**
 * 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.
 *
 * 

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. * *

This class extends {@link Number}, but does not define * methods such as {@code hashCode} and {@code compareTo} because * instances are expected to be mutated, and so are not useful as * collection keys. * *

jsr166e note: This class is targeted to be placed in * java.util.concurrent.atomic * * @since 1.8 * @author Doug Lea */ @GwtCompatible(emulated = true) final class LongAdder extends Striped64 implements Serializable, LongAddable { private static final long serialVersionUID = 7249069246863182397L; /** * Version of plus for use in retryUpdate */ final long fn(long v, long x) { return v + x; } /** * 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; HashCode hc; Cell a; int n; if ((as = cells) != null || !casBase(b = base, b + x)) { boolean uncontended = true; int h = (hc = threadHashCode.get()).code; if (as == null || (n = as.length) < 1 || (a = as[(n - 1) & h]) == null || !(uncontended = a.cas(v = a.value, v + x))) retryUpdate(x, hc, 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 NOT 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() { long sum = base; Cell[] as = cells; if (as != null) { int n = as.length; for (int i = 0; i < n; ++i) { Cell a = as[i]; if (a != 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() { internalReset(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 * not guaranteed to be the final value occurring before * the reset. * * @return the sum */ public long sumThenReset() { long sum = base; Cell[] as = cells; base = 0L; if (as != null) { int n = as.length; for (int i = 0; i < n; ++i) { Cell a = as[i]; if (a != 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(ObjectOutputStream s) throws java.io.IOException { s.defaultWriteObject(); s.writeLong(sum()); } private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException { s.defaultReadObject(); busy = 0; cells = null; base = s.readLong(); } }