Class DoubleAccumulator
- java.lang.Object
-
- java.lang.Number
-
- java.util.concurrent.atomic.DoubleAccumulator
- All Implemented Interfaces:
Serializable
public class DoubleAccumulator extends Number implements Serializable
One or more variables that together maintain a running 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.
- Since:
- 1.8
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
DoubleAccumulator(DoubleBinaryOperator accumulatorFunction,
double identity) | Creates a new instance using the given accumulator function and identity element. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | accumulate(double x) | Updates with the given value. |
double | doubleValue() | Equivalent to |
float | floatValue() | Returns the current value as a |
double | get() | Returns the current value. |
double | getThenReset() | |
int | intValue() | Returns the current value as an |
long | longValue() | Returns the current value as a |
void | reset() | Resets variables maintaining updates to the identity value. |
String | toString() | Returns the String representation of the current value. |
Methods declared in class java.lang.Number
byteValue, shortValue
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
DoubleAccumulator
public DoubleAccumulator(DoubleBinaryOperator accumulatorFunction, double identity)
Creates a new instance using the given accumulator function and identity element.
- Parameters:
-
accumulatorFunction
- a side-effect-free function of two arguments -
identity
- identity (initial value) for the accumulator function
Method Detail
accumulate
public void accumulate(double x)
Updates with the given value.
- Parameters:
-
x
- the value
get
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:
- the current value
reset
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.
getThenReset
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:
- the value before reset
toString
public String toString()
Returns the String representation of the current value.
doubleValue
public double doubleValue()
Equivalent to get()
.
- Specified by:
-
doubleValue
in classNumber
- Returns:
- the current value
longValue
public long longValue()
Returns the current value as a long
after a narrowing primitive conversion.
- Specified by:
-
longValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
long
.
intValue
public int intValue()
Returns the current value as an int
after a narrowing primitive conversion.
- Specified by:
-
intValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
int
.
floatValue
public float floatValue()
Returns the current value as a float
after a narrowing primitive conversion.
- Specified by:
-
floatValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion to type
float
.