Class LongAdder

java.lang.Object
java.lang.Number
java.util.concurrent.atomic.LongAdder
All Implemented Interfaces:
Serializable
public class LongAdder extends Number implements Serializable
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.

LongAdders can be used with a ConcurrentHashMap to maintain a scalable frequency map (a form of histogram or multiset). For example, to add a count to a ConcurrentHashMap<String,LongAdder> freqs, initializing if not already present, you can use freqs.computeIfAbsent(key, k -> new LongAdder()).increment();

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.

Since:
1.8
See Also:

  • Constructor Summary

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

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    add(long x)
    Adds the given value.
    void
    decrement()
    Equivalent to add(-1).
    double
    doubleValue()
    Returns the sum() as a double after a widening primitive conversion.
    float
    floatValue()
    Returns the sum() as a float after a widening primitive conversion.
    void
    increment()
    Equivalent to add(1).
    int
    intValue()
    Returns the sum() as an int after a narrowing primitive conversion.
    long
    longValue()
    Equivalent to sum().
    void
    reset()
    Resets variables maintaining the sum to zero.
    long
    sum()
    Returns the current sum.
    long
    sumThenReset()
    Equivalent in effect to sum() followed by reset().
    String
    toString()
    Returns the String representation of the sum().

    Methods declared in class Number

    byteValue, shortValue
    Modifier and Type
    Method
    Description
    byte
    byteValue()
    Returns the value of the specified number as a byte.
    short
    shortValue()
    Returns the value of the specified number as a short.

    Methods declared in class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
    boolean
    equals(Object o)
    Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    May cause performance issues, deadlocks and hangs.
    final Class<? extends Object>
    getClass()
    Answers the unique instance of java.lang.Class which represents the class of the receiver.
    int
    hashCode()
    Answers an integer hash code for the receiver.
    final void
    notify()
    Causes one thread which is waiting on the receiver to be made ready to run.
    final void
    notifyAll()
    Causes all threads which are waiting on the receiver to be made ready to run.
    final void
    wait()
    Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
    final void
    wait(long time)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
    final void
    wait(long time, int frac)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

  • Constructor Details

    • LongAdder

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

  • Method Details

    • add

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

    • increment

      public void increment()
      Equivalent to add(1).

    • 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.
      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
      Returns:
      the numeric value represented by this object after conversion to type int.

    • floatValue

      public float floatValue()
      Returns the sum() as a float after a widening primitive conversion.
      Specified by:
      floatValue in class Number
      Returns:
      the numeric value represented by this object after conversion to type float.

    • doubleValue

      public double doubleValue()
      Returns the sum() as a double after a widening primitive conversion.
      Specified by:
      doubleValue in class Number
      Returns:
      the numeric value represented by this object after conversion to type double.