LongAdder
open class LongAdder : Number, Serializable
| kotlin.Any | ||
| ↳ | kotlin.Number | |
| ↳ | java.util.concurrent.atomic.LongAdder | |
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 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.
Summary
| Public constructors | |
|---|---|
|
Creates a new adder with initial sum of zero. |
|
| Public methods | |
|---|---|
| open Unit |
Adds the given value. |
| open Unit |
Equivalent to |
| open Unit |
Equivalent to |
| open Unit |
reset()Resets variables maintaining the sum to zero. |
| open Long |
sum()Returns the current sum. |
| open Long | |
| open Double |
toDouble()Returns the |
| open Float |
toFloat()Returns the |
| open Int |
toInt()Returns the |
| open Long |
toLong()Equivalent to |
| open String |
toString()Returns the String representation of the |
Public constructors
Public methods
add
open fun add(x: Long): Unit
Adds the given value.
| Parameters | |
|---|---|
x |
Long: the value to add |
reset
open fun reset(): Unit
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
open fun sum(): Long
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.
| Return | |
|---|---|
Long |
the sum |
sumThenReset
open fun sumThenReset(): Long
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.
| Return | |
|---|---|
Long |
the sum |
toDouble
open fun toDouble(): Double
Returns the sum as a double after a widening primitive conversion.
| Return | |
|---|---|
Double |
the numeric value represented by this object after conversion to type double. |
toFloat
open fun toFloat(): Float
Returns the sum as a float after a widening primitive conversion.
| Return | |
|---|---|
Float |
the numeric value represented by this object after conversion to type float. |
toInt
open fun toInt(): Int
Returns the sum as an int after a narrowing primitive conversion.
| Return | |
|---|---|
Int |
the numeric value represented by this object after conversion to type int. |
toString
open fun toString(): String
Returns the String representation of the sum.
| Return | |
|---|---|
String |
the String representation of the sum |