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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package jsr166e; |
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import java.io.IOException; |
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import java.io.Serializable; |
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import java.io.ObjectInputStream; |
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import java.io.ObjectOutputStream; |
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|
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/** |
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* One or more variables that together maintain a running {@code long} |
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* maximum with initial value {@code Long.MIN_VALUE}. When updates |
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* (method {@link #update}) are contended across threads, the set of |
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* variables may grow dynamically to reduce contention. Method {@link |
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* #max} (or, equivalently, {@link #longValue}) returns the current |
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* maximum across the variables maintaining updates. |
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* |
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* <p>This class extends {@link Number}, but does <em>not</em> define |
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* methods such as {@code hashCode} and {@code compareTo} because |
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* instances are expected to be mutated, and so are not useful as |
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* collection keys. |
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* |
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* <p><em>jsr166e note: This class is targeted to be placed in |
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* java.util.concurrent.atomic<em> |
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* |
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* @author Doug Lea |
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*/ |
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public class LongMaxUpdater extends Striped64 implements Serializable { |
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private static final long serialVersionUID = 7249069246863182397L; |
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|
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/** |
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* Version of max for use in retryUpdate |
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*/ |
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final long fn(long v, long x) { return v > x ? v : x; } |
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|
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/** |
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* Creates a new instance with initial maximum of {@code |
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* Long.MIN_VALUE}. |
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*/ |
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public LongMaxUpdater() { |
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base = Long.MIN_VALUE; |
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} |
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|
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/** |
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* Updates the maximum to be at least the given value. |
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* |
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* @param x the value to update |
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*/ |
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public void update(long x) { |
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Cell[] as; long b, v; HashCode hc; Cell a; int n; |
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if ((as = cells) != null || |
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(b = base) < x && !casBase(b, x)) { |
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boolean uncontended = true; |
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int h = (hc = threadHashCode.get()).code; |
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if (as == null || (n = as.length) < 1 || |
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(a = as[(n - 1) & h]) == null || |
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((v = a.value) < x && !(uncontended = a.cas(v, x)))) |
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retryUpdate(x, hc, uncontended); |
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} |
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} |
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|
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/** |
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* Returns the current maximum. The returned value is |
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* <em>NOT</em> an atomic snapshot: Invocation in the absence of |
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* concurrent updates returns an accurate result, but concurrent |
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* updates that occur while the value is being calculated might |
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* not be incorporated. |
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* |
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* @return the maximum |
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*/ |
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public long max() { |
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Cell[] as = cells; |
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long max = base; |
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if (as != null) { |
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int n = as.length; |
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long v; |
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for (int i = 0; i < n; ++i) { |
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Cell a = as[i]; |
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if (a != null && (v = a.value) > max) |
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max = v; |
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} |
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} |
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return max; |
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} |
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|
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/** |
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* Resets variables maintaining updates to {@code Long.MIN_VALUE}. |
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* This method may be a useful alternative to creating a new |
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* updater, but is only effective if there are no concurrent |
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* updates. Because this method is intrinsically racy, it should |
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* only be used when it is known that no threads are concurrently |
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* updating. |
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*/ |
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public void reset() { |
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internalReset(Long.MIN_VALUE); |
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} |
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|
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/** |
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* Equivalent in effect to {@link #max} followed by {@link |
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* #reset}. This method may apply for example during quiescent |
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* points between multithreaded computations. If there are |
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* updates concurrent with this method, the returned value is |
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* <em>not</em> guaranteed to be the final value occurring before |
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* the reset. |
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* |
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* @return the maximum |
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*/ |
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public long maxThenReset() { |
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Cell[] as = cells; |
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long max = base; |
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base = Long.MIN_VALUE; |
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if (as != null) { |
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int n = as.length; |
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for (int i = 0; i < n; ++i) { |
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Cell a = as[i]; |
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if (a != null) { |
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long v = a.value; |
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a.value = Long.MIN_VALUE; |
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if (v > max) |
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max = v; |
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} |
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} |
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} |
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return max; |
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} |
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|
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/** |
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* Returns the String representation of the {@link #max}. |
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* @return the String representation of the {@link #max}. |
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*/ |
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public String toString() { |
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return Long.toString(max()); |
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} |
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|
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/** |
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* Equivalent to {@link #max}. |
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* |
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* @return the maximum |
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*/ |
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public long longValue() { |
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return max(); |
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} |
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|
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/** |
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* Returns the {@link #max} as an {@code int} after a narrowing |
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* primitive conversion. |
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*/ |
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public int intValue() { |
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return (int)max(); |
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} |
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|
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/** |
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* Returns the {@link #max} as a {@code float} |
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* after a widening primitive conversion. |
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*/ |
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public float floatValue() { |
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return (float)max(); |
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} |
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|
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/** |
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* Returns the {@link #max} as a {@code double} after a widening |
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* primitive conversion. |
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*/ |
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public double doubleValue() { |
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return (double)max(); |
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} |
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|
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private void writeObject(java.io.ObjectOutputStream s) |
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throws java.io.IOException { |
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s.defaultWriteObject(); |
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s.writeLong(max()); |
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} |
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|
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private void readObject(ObjectInputStream s) |
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throws IOException, ClassNotFoundException { |
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s.defaultReadObject(); |
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busy = 0; |
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cells = null; |
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base = s.readLong(); |
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} |
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|
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} |