Class LongAdder

All Implemented Interfaces:
LongAddable, Serializable

final class LongAdder extends Striped64 implements Serializable, LongAddable
One or more variables that together maintain an initially zero long sum. When updates (method add(long)) are contended across threads, the set of variables may grow dynamically to reduce contention. Method sum() (or, equivalently, longValue()) returns the current total combined across the variables maintaining the sum.

This class is usually preferable to 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.

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
  • Field Details

  • Constructor Details

    • LongAdder

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

    • fn

      final long fn(long v, long x)
      Version of plus for use in retryUpdate
      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(long x)
      Adds the given value.
      Specified by:
      add in interface LongAddable
      Parameters:
      x - the value to add
    • increment

      public void increment()
      Equivalent to add(1).
      Specified by:
      increment in interface LongAddable
    • decrement

      public void decrement()
      Equivalent to add(-1).
    • sum

      public long 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.
      Specified by:
      sum in interface LongAddable
      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.
    • sumThenReset

      public long 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()
    • longValue

      public long longValue()
      Equivalent to sum().
      Specified by:
      longValue in class Number
      Returns:
      the sum
    • 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 widening primitive conversion.
      Specified by:
      floatValue in class Number
    • doubleValue

      public double doubleValue()
      Returns the sum() as a double after a widening primitive conversion.
      Specified by:
      doubleValue 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