One or more variables that together maintain a running double 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, doubleValue) returns the current value across the variables maintaining updates.

This class is usually preferable to alternatives when multiple threads update a common value that is used for purposes such as summary statistics that are frequently updated but less frequently read.

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 commutative and associative within the floating point tolerance required in usage contexts. 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 Double::max along with Double.NEGATIVE_INFINITY as the identity. The order of accumulation within or across threads is not guaranteed. Thus, this class may not be applicable if numerical stability is required, especially when combining values of substantially different orders of magnitude.

Class DoubleAdder provides analogs of the functionality of this class for the common special case of maintaining sums. The call new DoubleAdder() is equivalent to new DoubleAccumulator((x, y) -> x + y, 0.0).

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	DoubleAccumulator.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 DoubleBinaryOperator	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	DoubleAccumulator(DoubleBinaryOperator a side-effect-free function of two arguments accumulatorFunction, double 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(double the value x) Updates with the given value.
public double	Returns: the current value doubleValue() Implements abstract java.lang.Number.doubleValue. Equivalent to `get`.
public float	floatValue() Implements abstract java.lang.Number.floatValue. Returns the current value as a `float` after a narrowing primitive conversion.
public double	Returns: the current value get() Returns the current value.
public double	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	longValue() Implements abstract java.lang.Number.longValue. Returns the current value as a `long` after a narrowing primitive conversion.
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 DoubleBinaryOperator 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

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

DoubleAccumulator

back to summary

public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity)

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

Parameters

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

Method Detail

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

accumulate

back to summary

public void accumulate(double x)

Updates with the given value.

Parameters

x:double: the value

doubleValue back to summary

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

public double doubleValue()

Implements abstract java.lang.Number.doubleValue.

Equivalent to get.

Returns:double: the current value

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 narrowing primitive conversion.

public float floatValue()

Implements abstract java.lang.Number.floatValue.

Returns the current value as a float after a narrowing primitive conversion.

get	back to summary
public double 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:double the current value

get

back to summary

public double 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:double: the current value

getThenReset back to summary

getThenReset	back to summary
public double 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:double the value before reset

public double 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:double: 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.

public int intValue()

Implements abstract java.lang.Number.intValue.

Returns the current value as an int after a narrowing primitive conversion.

longValue back to summary

longValue	back to summary
public long longValue() Implements abstract java.lang.Number.longValue. Returns the current value as a `long` after a narrowing primitive conversion.

public long longValue()

Implements abstract java.lang.Number.longValue.

Returns the current value as a long after a narrowing primitive conversion.

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 DoubleAccumulator.SerializationProxy

Class Inheritance

extends Object
implements Serializable

java.lang.Object
java.util.concurrent.atomic.DoubleAccumulator.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 DoubleBinaryOperator	function The function used for updates.
private final long	identity The identity value, represented as a long, as converted by `Double#doubleToRawLongBits`.
private static final long	serialVersionUID
private final double	value The current value returned by get().

Constructor Summary

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

Method Summary

Modifier and Type	Method and Description
private Object	Returns: a `DoubleAccumulator` object with initial state held by this proxy readResolve() Returns a `DoubleAccumulator` 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 DoubleBinaryOperator function The function used for updates. Annotations @SuppressWarnings:serial

identity	back to summary
private final long identity The identity value, represented as a long, as converted by `Double#doubleToRawLongBits`. The original identity can be recovered using `Double#longBitsToDouble`.

serialVersionUID	back to summary
private static final long serialVersionUID

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

Constructor Detail

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

Method Detail

readResolve back to summary

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

private Object readResolve()

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

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

public Class DoubleAccumulator

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private Class DoubleAccumulator.SerializationProxy

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail