Serializable
public class LongAccumulator extends Number implements Serializable
long
value updated using a supplied function. When updates (method accumulate(long)
) 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.
Constructor | Description |
---|---|
LongAccumulator |
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() |
Returns the current value as a double after a widening primitive conversion. |
float |
floatValue() |
Returns the current value as a float after a widening primitive conversion. |
long |
get() |
Returns the current value. |
long |
getThenReset() |
|
int |
intValue() |
Returns the current value as an int after a narrowing primitive conversion. |
long |
longValue() |
Equivalent to get() . |
void |
reset() |
Resets variables maintaining updates to the identity value. |
String |
toString() |
Returns the String representation of the current value. |
byteValue, shortValue
public LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)
accumulatorFunction
- a side-effect-free function of two argumentsidentity
- identity (initial value) for the accumulator functionpublic void accumulate(long x)
x
- the valuepublic long get()
public void reset()
public long 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 long longValue()
get()
.public int intValue()
int
after a narrowing primitive conversion.public float floatValue()
float
after a widening primitive conversion.floatValue
in class Number
float
.public double doubleValue()
double
after a widening primitive conversion.doubleValue
in class Number
double
.
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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/LongAccumulator.html