luni/src/main/java/java/util/concurrent/atomic/DoubleAccumulator.java - platform/libcore - Git at Google

 /*
  * 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.DoubleBinaryOperator;

 /**
  * One or more variables that together maintain a running {@code double}
  * 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 #doubleValue}) returns the current value
  * across the variables maintaining updates.
  *
  * <p>This class is usually preferable to alternatives when multiple
  * threads update a common value that is used for purposes such as
  * summary statistics that are frequently updated but less frequently
  * read.
  *
  * <p>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 Double::max} along with {@code
  * Double.NEGATIVE_INFINITY} as the identity. The order of
  * accumulation within or across threads is not guaranteed. Thus, this
  * class may not be applicable if numerical stability is required,
  * especially when combining values of substantially different orders
  * of magnitude.
  *
  * <p>Class {@link DoubleAdder} provides analogs of the functionality
  * of this class for the common special case of maintaining sums.  The
  * call {@code new DoubleAdder()} is equivalent to {@code new
  * DoubleAccumulator((x, y) -> x + y, 0.0)}.
  *
  * <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 DoubleAccumulator extends Striped64 implements Serializable {
     private static final long serialVersionUID = 7249069246863182397L;

     private final DoubleBinaryOperator function;
     private final long identity; // use long representation

     /**
      * Creates a new instance using the given accumulator function
      * and identity element.
      * @param accumulatorFunction a side-effect-free function of two arguments
      * @param identity identity (initial value) for the accumulator function
      */
     public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction,
                              double identity) {
         this.function = accumulatorFunction;
         base = this.identity = Double.doubleToRawLongBits(identity);
     }

     /**
      * Updates with the given value.
      *
      * @param x the value
      */
     public void accumulate(double x) {
         Cell[] as; long b, v, r; int m; Cell a;
         if ((as = cells) != null ||
             (r = Double.doubleToRawLongBits
              (function.applyAsDouble
               (Double.longBitsToDouble(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 = Double.doubleToRawLongBits
                    (function.applyAsDouble
                     (Double.longBitsToDouble(v = a.value), x))) == v ||
                   a.cas(v, r)))
                 doubleAccumulate(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 double get() {
         Cell[] as = cells;
         double result = Double.longBitsToDouble(base);
         if (as != null) {
             for (Cell a : as)
                 if (a != null)
                     result = function.applyAsDouble
                         (result, Double.longBitsToDouble(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;
         base = identity;
         if (as != null) {
             for (Cell a : as)
                 if (a != null)
                     a.reset(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 double getThenReset() {
         Cell[] as = cells;
         double result = Double.longBitsToDouble(base);
         base = identity;
         if (as != null) {
             for (Cell a : as) {
                 if (a != null) {
                     double v = Double.longBitsToDouble(a.value);
                     a.reset(identity);
                     result = function.applyAsDouble(result, v);
                 }
             }
         }
         return result;
     }

     /**
      * Returns the String representation of the current value.
      * @return the String representation of the current value
      */
     public String toString() {
         return Double.toString(get());
     }

     /**
      * Equivalent to {@link #get}.
      *
      * @return the current value
      */
     public double doubleValue() {
         return get();
     }

     /**
      * Returns the {@linkplain #get current value} as a {@code long}
      * after a narrowing primitive conversion.
      */
     public long longValue() {
         return (long)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 narrowing primitive conversion.
      */
     public float floatValue() {
         return (float)get();
     }

     /**
      * Serialization proxy, used to avoid reference to the non-public
      * Striped64 superclass in serialized forms.
      * @serial include
      */
     private static class SerializationProxy implements Serializable {
         private static final long serialVersionUID = 7249069246863182397L;

         /**
          * The current value returned by get().
          * @serial
          */
         private final double value;

         /**
          * The function used for updates.
          * @serial
          */
         private final DoubleBinaryOperator function;

         /**
          * The identity value, represented as a long, as converted by
          * {@link Double#doubleToRawLongBits}.  The original identity
          * can be recovered using {@link Double#longBitsToDouble}.
          * @serial
          */
         private final long identity;

         SerializationProxy(double value,
                            DoubleBinaryOperator function,
                            long identity) {
             this.value = value;
             this.function = function;
             this.identity = identity;
         }

         /**
          * Returns a {@code DoubleAccumulator} object with initial state
          * held by this proxy.
          *
          * @return a {@code DoubleAccumulator} object with initial state
          * held by this proxy
          */
         private Object readResolve() {
             double d = Double.longBitsToDouble(identity);
             DoubleAccumulator a = new DoubleAccumulator(function, d);
             a.base = Double.doubleToRawLongBits(value);
             return a;
         }
     }

     /**
      * Returns a
      * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAccumulator.SerializationProxy">
      * SerializationProxy</a>
      * representing the state of this instance.
      *
      * @return a {@link SerializationProxy}
      * representing the state of this instance
      */
     private Object writeReplace() {
         return new SerializationProxy(get(), function, identity);
     }

     /**
      * @param s the stream
      * @throws java.io.InvalidObjectException always
      */
     private void readObject(java.io.ObjectInputStream s)
         throws java.io.InvalidObjectException {
         throw new java.io.InvalidObjectException("Proxy required");
     }

 }
	/*
	* 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.DoubleBinaryOperator;

	/**
	* One or more variables that together maintain a running {@code double}
	* 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 #doubleValue}) returns the current value
	* across the variables maintaining updates.
	*
	* <p>This class is usually preferable to alternatives when multiple
	* threads update a common value that is used for purposes such as
	* summary statistics that are frequently updated but less frequently
	* read.
	*
	* <p>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 Double::max} along with {@code
	* Double.NEGATIVE_INFINITY} as the identity. The order of
	* accumulation within or across threads is not guaranteed. Thus, this
	* class may not be applicable if numerical stability is required,
	* especially when combining values of substantially different orders
	* of magnitude.
	*
	* <p>Class {@link DoubleAdder} provides analogs of the functionality
	* of this class for the common special case of maintaining sums. The
	* call {@code new DoubleAdder()} is equivalent to {@code new
	* DoubleAccumulator((x, y) -> x + y, 0.0)}.
	*
	* <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 DoubleAccumulator extends Striped64 implements Serializable {
	private static final long serialVersionUID = 7249069246863182397L;

	private final DoubleBinaryOperator function;
	private final long identity; // use long representation

	/**
	* Creates a new instance using the given accumulator function
	* and identity element.
	* @param accumulatorFunction a side-effect-free function of two arguments
	* @param identity identity (initial value) for the accumulator function
	*/
	public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction,
	double identity) {
	this.function = accumulatorFunction;
	base = this.identity = Double.doubleToRawLongBits(identity);
	}

	/**
	* Updates with the given value.
	*
	* @param x the value
	*/
	public void accumulate(double x) {
	Cell[] as; long b, v, r; int m; Cell a;
	if ((as = cells) != null \|\|
	(r = Double.doubleToRawLongBits
	(function.applyAsDouble
	(Double.longBitsToDouble(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 = Double.doubleToRawLongBits
	(function.applyAsDouble
	(Double.longBitsToDouble(v = a.value), x))) == v \|\|
	a.cas(v, r)))
	doubleAccumulate(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 double get() {
	Cell[] as = cells;
	double result = Double.longBitsToDouble(base);
	if (as != null) {
	for (Cell a : as)
	if (a != null)
	result = function.applyAsDouble
	(result, Double.longBitsToDouble(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;
	base = identity;
	if (as != null) {
	for (Cell a : as)
	if (a != null)
	a.reset(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 double getThenReset() {
	Cell[] as = cells;
	double result = Double.longBitsToDouble(base);
	base = identity;
	if (as != null) {
	for (Cell a : as) {
	if (a != null) {
	double v = Double.longBitsToDouble(a.value);
	a.reset(identity);
	result = function.applyAsDouble(result, v);
	}
	}
	}
	return result;
	}

	/**
	* Returns the String representation of the current value.
	* @return the String representation of the current value
	*/
	public String toString() {
	return Double.toString(get());
	}

	/**
	* Equivalent to {@link #get}.
	*
	* @return the current value
	*/
	public double doubleValue() {
	return get();
	}

	/**
	* Returns the {@linkplain #get current value} as a {@code long}
	* after a narrowing primitive conversion.
	*/
	public long longValue() {
	return (long)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 narrowing primitive conversion.
	*/
	public float floatValue() {
	return (float)get();
	}

	/**
	* Serialization proxy, used to avoid reference to the non-public
	* Striped64 superclass in serialized forms.
	* @serial include
	*/
	private static class SerializationProxy implements Serializable {
	private static final long serialVersionUID = 7249069246863182397L;

	/**
	* The current value returned by get().
	* @serial
	*/
	private final double value;

	/**
	* The function used for updates.
	* @serial
	*/
	private final DoubleBinaryOperator function;

	/**
	* The identity value, represented as a long, as converted by
	* {@link Double#doubleToRawLongBits}. The original identity
	* can be recovered using {@link Double#longBitsToDouble}.
	* @serial
	*/
	private final long identity;

	SerializationProxy(double value,
	DoubleBinaryOperator function,
	long identity) {
	this.value = value;
	this.function = function;
	this.identity = identity;
	}

	/**
	* Returns a {@code DoubleAccumulator} object with initial state
	* held by this proxy.
	*
	* @return a {@code DoubleAccumulator} object with initial state
	* held by this proxy
	*/
	private Object readResolve() {
	double d = Double.longBitsToDouble(identity);
	DoubleAccumulator a = new DoubleAccumulator(function, d);
	a.base = Double.doubleToRawLongBits(value);
	return a;
	}
	}

	/**
	* Returns a
	* <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAccumulator.SerializationProxy">
	* SerializationProxy</a>
	* representing the state of this instance.
	*
	* @return a {@link SerializationProxy}
	* representing the state of this instance
	*/
	private Object writeReplace() {
	return new SerializationProxy(get(), function, identity);
	}

	/**
	* @param s the stream
	* @throws java.io.InvalidObjectException always
	*/
	private void readObject(java.io.ObjectInputStream s)
	throws java.io.InvalidObjectException {
	throw new java.io.InvalidObjectException("Proxy required");
	}

	}