Serializable
public class DoubleAccumulator extends Number implements Serializable
double
value updated using a supplied function. When updates (method accumulate(double)
) 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.
Constructor | Description |
---|---|
DoubleAccumulator |
Creates a new instance using the given accumulator function and identity element. |
Modifier and Type | Method | Description |
---|---|---|
void |
accumulate |
Updates with the given value. |
double |
doubleValue() |
Equivalent to get() . |
float |
floatValue() |
Returns the current value as a float after a narrowing primitive conversion. |
double |
get() |
Returns the current value. |
double |
getThenReset() |
|
int |
intValue() |
Returns the current value as an int after a narrowing primitive conversion. |
long |
longValue() |
Returns the current value as a long after a narrowing primitive conversion. |
void |
reset() |
Resets variables maintaining updates to the identity value. |
String |
toString() |
Returns the String representation of the current value. |
byteValue, shortValue
public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity)
accumulatorFunction
- a side-effect-free function of two argumentsidentity
- identity (initial value) for the accumulator functionpublic void accumulate(double x)
x
- the valuepublic double get()
public void reset()
public double getThenReset()
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.public String toString()
public double doubleValue()
get()
.doubleValue
in class Number
public long longValue()
long
after a narrowing primitive conversion.public int intValue()
int
after a narrowing primitive conversion.public float floatValue()
float
after a narrowing primitive conversion.floatValue
in class Number
float
.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/atomic/DoubleAccumulator.html