One or more variables that together maintain a running long value updated using a supplied function. When updates (method accumulate) are contended across threads, the set of variables may grow dynamically to reduce contention. Method get (or, equivalently, longValue) returns the current value across the variables maintaining updates.

This class is usually preferable to AtomicLong when multiple threads update a common value 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.

The order of accumulation within or across threads is not guaranteed and cannot be depended upon, so this class is only applicable to functions for which the order of accumulation does not matter. The supplied accumulator function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. For predictable results, the accumulator function should be associative and commutative. The function is applied with an existing value (or identity) as one argument, and a given update as the other argument. For example, to maintain a running maximum value, you could supply Long::max along with Long.MIN_VALUE as the identity.

Class LongAdder provides analogs of the functionality of this class for the common special case of maintaining counts and sums. The call new LongAdder() is equivalent to new LongAccumulator((x, y) -> x + y, 0L).

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	LongAccumulator.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 final LongBinaryOperator	function
private final long	identity
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	LongAccumulator(LongBinaryOperator a side-effect-free function of two arguments accumulatorFunction, long identity (initial value) for the accumulator function identity) Creates a new instance using the given accumulator function and identity element.

Method Summary

Modifier and Type	Method and Description
public void	accumulate(long the value x) Updates with the given value.
public double	doubleValue() Implements abstract java.lang.Number.doubleValue. Returns the current value as a `double` after a widening primitive conversion.
public float	floatValue() Implements abstract java.lang.Number.floatValue. Returns the current value as a `float` after a widening primitive conversion.
public long	Returns: the current value get() Returns the current value.
public long	Returns: the value before reset getThenReset() Equivalent in effect to `get` followed by `reset`.
public int	intValue() Implements abstract java.lang.Number.intValue. Returns the current value as an `int` after a narrowing primitive conversion.
public long	Returns: the current value longValue() Implements abstract java.lang.Number.longValue. Equivalent to `get`.
private void	readObject(ObjectInputStream the stream s)
public void	reset() Resets variables maintaining updates to the identity value.
public String	Returns: the String representation of the current value toString() Overrides java.lang.Object.toString. Returns the String representation of the current value.
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

function	back to summary
private final LongBinaryOperator function Annotations @SuppressWarnings:serial

identity	back to summary
private final long identity

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

Constructor Detail

LongAccumulator	back to summary
public LongAccumulator(LongBinaryOperator accumulatorFunction, long identity) Creates a new instance using the given accumulator function and identity element. Parameters accumulatorFunction:LongBinaryOperator a side-effect-free function of two arguments identity:long identity (initial value) for the accumulator function

LongAccumulator

back to summary

public LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)

Creates a new instance using the given accumulator function and identity element.

Parameters

accumulatorFunction:LongBinaryOperator: a side-effect-free function of two arguments
identity:long: identity (initial value) for the accumulator function

Method Detail

accumulate	back to summary
public void accumulate(long x) Updates with the given value. Parameters x:long the value

accumulate

back to summary

public void accumulate(long x)

Updates with the given value.

Parameters

x:long: the value

doubleValue back to summary

doubleValue	back to summary
public double doubleValue() Implements abstract java.lang.Number.doubleValue. Returns the current value 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 current value 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 current value 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 current value 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.

get	back to summary
public long get() Returns the current value. 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 value is being calculated might not be incorporated. Returns:long the current value

get

back to summary

public long get()

Returns the current value. 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 value is being calculated might not be incorporated.

Returns:long: the current value

getThenReset back to summary

getThenReset	back to summary
public long getThenReset() Equivalent in effect to `get` 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 value before reset

public long getThenReset()

Equivalent in effect to get 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 value before reset

intValue back to summary

intValue	back to summary
public int intValue() Implements abstract java.lang.Number.intValue. Returns the current value 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 current value 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 `get`. Returns:long the current value

public long longValue()

Implements abstract java.lang.Number.longValue.

Equivalent to get.

Returns:long: the current value

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 updates to the identity value. This method may be a useful alternative to creating a new updater, 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.

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

toString

back to summary

public String toString()

Overrides java.lang.Object.toString.

Returns the String representation of the current value.

Returns:String: the String representation of the current value

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 LongAccumulator.SerializationProxy

Class Inheritance

extends Object
implements Serializable

java.lang.Object
java.util.concurrent.atomic.LongAccumulator.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 final LongBinaryOperator	function The function used for updates.
private final long	identity The identity value.
private static final long	serialVersionUID
private final long	value The current value returned by get().

Constructor Summary

Access	Constructor and Description
pack-priv	SerializationProxy(long value, LongBinaryOperator function, long identity)

Method Summary

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

function	back to summary
private final LongBinaryOperator function The function used for updates. Annotations @SuppressWarnings:serial

identity	back to summary
private final long identity The identity value.

serialVersionUID	back to summary
private static final long serialVersionUID

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

Constructor Detail

SerializationProxy	back to summary
pack-priv SerializationProxy(long value, LongBinaryOperator function, long identity)

Method Detail

readResolve back to summary

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

private Object readResolve()

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

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

public Class LongAccumulator

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private Class LongAccumulator.SerializationProxy

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail