Package io.prometheus.client

Class DoubleAdder

  • All Implemented Interfaces:
    java.io.Serializable
    public class DoubleAdder
extends Striped64
implements java.io.Serializable
    One or more variables that together maintain an initially zero double sum. When updates (method add(double)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method sum() (or, equivalently doubleValue()) returns the current total combined across the variables maintaining the sum.

    This class extends Number, but does not define methods such as equals, hashCode and 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
    See Also:
    Serialized Form

    • Constructor Summary

      Constructors 
      Constructor Description
      DoubleAdder()
      Creates a new adder with initial sum of zero.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void add​(double x)
      Adds the given value.
      double doubleValue()
      Equivalent to sum().
      float floatValue()
      Returns the sum() as a float after a narrowing primitive conversion.
      (package private) long fn​(long v, long x)
      Update function.
      int intValue()
      Returns the sum() as an int after a narrowing primitive conversion.
      long longValue()
      Returns the sum() as a long after a narrowing primitive conversion.
      private void readObject​(java.io.ObjectInputStream s)  
      void reset()
      Resets variables maintaining the sum to zero.
      void set​(double x)  
      double sum()
      Returns the current sum.
      double sumThenReset()
      Equivalent in effect to sum() followed by reset().
      java.lang.String toString()
      Returns the String representation of the sum().
      private void writeObject​(java.io.ObjectOutputStream s)  

      • Methods inherited from class java.lang.Number

        byteValue, shortValue

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

    • Constructor Detail

      • DoubleAdder

        public DoubleAdder()
        Creates a new adder with initial sum of zero.

    • Method Detail

      • fn

        final long fn​(long v,
              long x)
        Update function. Note that we must use "long" for underlying representations, because there is no compareAndSet for double, due to the fact that the bitwise equals used in any CAS implementation is not the same as double-precision equals. However, we use CAS only to detect and alleviate contention, for which bitwise equals works best anyway. In principle, the long/double conversions used here should be essentially free on most platforms since they just re-interpret bits. Similar conversions are used in other methods.
        Specified by:
        fn in class Striped64
        Parameters:
        v - the current value (of either base or a cell)
        x - the argument from a user update call
        Returns:
        result of the update function

      • add

        public void add​(double x)
        Adds the given value.
        Parameters:
        x - the value to add

      • sum

        public double sum()
        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. Also, because floating-point arithmetic is not strictly associative, the returned result need not be identical to the value that would be obtained in a sequential series of updates to a single variable.
        Returns:
        the sum

      • reset

        public void reset()
        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.

      • set

        public void set​(double x)

      • sumThenReset

        public double sumThenReset()
        Equivalent in effect to sum() followed by 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.
        Returns:
        the sum

      • toString

        public java.lang.String toString()
        Returns the String representation of the sum().
        Overrides:
        toString in class java.lang.Object
        Returns:
        the String representation of the sum()

      • doubleValue

        public double doubleValue()
        Equivalent to sum().
        Specified by:
        doubleValue in class java.lang.Number
        Returns:
        the sum

      • longValue

        public long longValue()
        Returns the sum() as a long after a narrowing primitive conversion.
        Specified by:
        longValue in class java.lang.Number

      • intValue

        public int intValue()
        Returns the sum() as an int after a narrowing primitive conversion.
        Specified by:
        intValue in class java.lang.Number

      • floatValue

        public float floatValue()
        Returns the sum() as a float after a narrowing primitive conversion.
        Specified by:
        floatValue in class java.lang.Number

      • writeObject

        private void writeObject​(java.io.ObjectOutputStream s)
                  throws java.io.IOException
        Throws:
        java.io.IOException

      • readObject

        private void readObject​(java.io.ObjectInputStream s)
                 throws java.io.IOException,
                        java.lang.ClassNotFoundException
        Throws:
        java.io.IOException
        java.lang.ClassNotFoundException