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Diffstat (limited to 'kamon-core/src/main/java/kamon/jsr166/LongAdder.java')
| -rw-r--r-- | kamon-core/src/main/java/kamon/jsr166/LongAdder.java | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/kamon-core/src/main/java/kamon/jsr166/LongAdder.java b/kamon-core/src/main/java/kamon/jsr166/LongAdder.java new file mode 100644 index 00000000..18f91759 --- /dev/null +++ b/kamon-core/src/main/java/kamon/jsr166/LongAdder.java @@ -0,0 +1,209 @@ +/* + +Note: this was copied from Doug Lea's CVS repository + http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/ + +LongAdder.java version 1.14 + +*/ + + +/* + * 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 kamon.jsr166; + +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 java.util.concurrent.atomic.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>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. + * + * <p><em>jsr166e note: This class is targeted to be placed in + * java.util.concurrent.atomic.</em> + * + * @since 1.8 + * @author Doug Lea + */ +public class LongAdder extends Striped64 implements Serializable { + 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 <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() { + 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 + * <em>not</em> 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(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(); + busy = 0; + cells = null; + base = s.readLong(); + } + +} |