One or more variables that together maintain an initially zero long sum. When updates (method add) 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 java.util.concurrent.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.

Nested and Inner Type Summary

Modifier and Type	Class and Description
private static class	LongAdder.SerializationProxy Serialization proxy, used to avoid reference to the non-public Striped64 superclass in serialized forms.

Field Summary

Modifier and Type	Field and Description
private static final long	serialVersionUID Hides java.lang.Number.serialVersionUID.

Inherited from java.util.concurrent.atomic.Striped64:: base cells cellsBusy NCPU

Constructor Summary

Access	Constructor and Description
public	LongAdder() Creates a new adder with initial sum of zero.

Method Summary

Modifier and Type	Method and Description
public void	add(long the value to add x) Adds the given value.
public void	decrement() Equivalent to `add(-1)`.
public double	doubleValue() Implements abstract java.lang.Number.doubleValue. Returns the `sum` as a `double` after a widening primitive conversion.
public float	floatValue() Implements abstract java.lang.Number.floatValue. Returns the `sum` as a `float` after a widening primitive conversion.
public void	increment() Equivalent to `add(1)`.
public int	intValue() Implements abstract java.lang.Number.intValue. Returns the `sum` as an `int` after a narrowing primitive conversion.
public long	Returns: the sum longValue() Implements abstract java.lang.Number.longValue. Equivalent to `sum`.
private void	readObject(ObjectInputStream the stream s)
public void	reset() Resets variables maintaining the sum to zero.
public long	Returns: the sum sum() Returns the current sum.
public long	Returns: the sum sumThenReset() Equivalent in effect to `sum` followed by `reset`.
public String	Returns: the String representation of the `sum` toString() Overrides java.lang.Object.toString. Returns the String representation of the `sum`.
private Object	Returns: a `SerializationProxy` representing the state of this instance writeReplace() Returns a SerializationProxy representing the state of this instance.

Inherited from java.util.concurrent.atomic.Striped64:: advanceProbe casBase casCellsBusy doubleAccumulate getAndSetBase getProbe longAccumulate

Field Detail

serialVersionUID	back to summary
private static final long serialVersionUID Hides java.lang.Number.serialVersionUID.

Constructor Detail

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

Method Detail

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

add

back to summary

public void add(long x)

Adds the given value.

Parameters

x:long: the value to add

decrement	back to summary
public void decrement() Equivalent to `add(-1)`.

doubleValue back to summary

doubleValue	back to summary
public double doubleValue() Implements abstract java.lang.Number.doubleValue. Returns the `sum` as a `double` after a widening primitive conversion. Returns:double Doc from java.lang.Number.doubleValue. the numeric value represented by this object after conversion to type `double`.

public double doubleValue()

Implements abstract java.lang.Number.doubleValue.

Returns the sum as a double after a widening primitive conversion.

Returns:double

Doc from java.lang.Number.doubleValue.

the numeric value represented by this object after conversion to type double.

floatValue back to summary

floatValue	back to summary
public float floatValue() Implements abstract java.lang.Number.floatValue. Returns the `sum` as a `float` after a widening primitive conversion. Returns:float Doc from java.lang.Number.floatValue. the numeric value represented by this object after conversion to type `float`.

public float floatValue()

Implements abstract java.lang.Number.floatValue.

Returns the sum as a float after a widening primitive conversion.

Returns:float

Doc from java.lang.Number.floatValue.

the numeric value represented by this object after conversion to type float.

increment	back to summary
public void increment() Equivalent to `add(1)`.

intValue back to summary

intValue	back to summary
public int intValue() Implements abstract java.lang.Number.intValue. Returns the `sum` as an `int` after a narrowing primitive conversion. Returns:int Doc from java.lang.Number.intValue. the numeric value represented by this object after conversion to type `int`.

public int intValue()

Implements abstract java.lang.Number.intValue.

Returns the sum as an int after a narrowing primitive conversion.

Returns:int

Doc from java.lang.Number.intValue.

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

longValue back to summary

longValue	back to summary
public long longValue() Implements abstract java.lang.Number.longValue. Equivalent to `sum`. Returns:long the sum

public long longValue()

Implements abstract java.lang.Number.longValue.

Equivalent to sum.

Returns:long: the sum

readObject	back to summary
private void readObject(ObjectInputStream s) throws InvalidObjectException Parameters s:ObjectInputStream the stream Exceptions InvalidObjectException: always

reset	back to summary
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.

sum	back to summary
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:long the sum

sum

back to summary

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:long: the sum

sumThenReset back to summary

sumThenReset	back to summary
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:long the sum

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:long: the sum

toString back to summary

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Returns the String representation of the `sum`. Returns:String the String representation of the `sum`

public String toString()

Overrides java.lang.Object.toString.

Returns the String representation of the sum.

Returns:String: the String representation of the sum

writeReplace back to summary

writeReplace	back to summary
private Object writeReplace() Returns a SerializationProxy representing the state of this instance. Returns:Object a `SerializationProxy` representing the state of this instance

private Object writeReplace()

Returns a SerializationProxy representing the state of this instance.

Returns:Object: a SerializationProxy representing the state of this instance

java.util.concurrent.atomic back to summary

private Class LongAdder.SerializationProxy

Class Inheritance

extends Object
implements Serializable

java.lang.Object
java.util.concurrent.atomic.LongAdder.SerializationProxy

All Implemented Interfaces

java.io.Serializable

Serialization proxy, used to avoid reference to the non-public Striped64 superclass in serialized forms.

Field Summary

Modifier and Type	Field and Description
private static final long	serialVersionUID
private final long	value The current value returned by sum().

Constructor Summary

Access	Constructor and Description
pack-priv	SerializationProxy(LongAdder a)

Method Summary

Modifier and Type	Method and Description
private Object	Returns: a `LongAdder` object with initial state held by this proxy readResolve() Returns a `LongAdder` object with initial state held by this proxy.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

serialVersionUID	back to summary
private static final long serialVersionUID

value	back to summary
private final long value The current value returned by sum().

Constructor Detail

SerializationProxy	back to summary
pack-priv SerializationProxy(LongAdder a)

Method Detail

readResolve back to summary

readResolve	back to summary
private Object readResolve() Returns a `LongAdder` object with initial state held by this proxy. Returns:Object a `LongAdder` object with initial state held by this proxy

private Object readResolve()

Returns a LongAdder object with initial state held by this proxy.

Returns:Object: a LongAdder object with initial state held by this proxy

public Class LongAdder

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private Class LongAdder.SerializationProxy

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail