Class DoubleAdder

All Implemented Interfaces:
Serializable

public class DoubleAdder extends Striped64 implements 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:
  • Field Details

  • Constructor Details

    • DoubleAdder

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

    • 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 String toString()
      Returns the String representation of the sum().
      Overrides:
      toString in class Object
      Returns:
      the String representation of the sum()
    • doubleValue

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

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

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

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

      private void writeObject(ObjectOutputStream s) throws IOException
      Throws:
      IOException
    • readObject

      private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException
      Throws:
      IOException
      ClassNotFoundException