- All Implemented Interfaces:
public class LongAccumulator extends Number implements Serializable
longvalue 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
longValue()) returns the current value across the variables maintaining updates.
This class is usually preferable to
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
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.
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
LongAccumulator((x, y) -> x + y, 0L).
This class extends
Number, but does not define
methods such as
compareTo because instances are expected to be mutated, and so are
not useful as collection keys.
- See Also:
- Serialized Form
LongBinaryOperator accumulatorFunction, long identity)(Creates a new instance using the given accumulator function and identity element.
Method SummaryModifier and TypeMethodDescription
(long x)Updates with the given value.
()Returns the current value.
()Resets variables maintaining updates to the identity value.
()Returns the String representation of the current value.
LongAccumulatorpublic LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)Creates a new instance using the given accumulator function and identity element.
accumulatorFunction- a side-effect-free function of two arguments
identity- identity (initial value) for the accumulator function
accumulatepublic void accumulate(long x)Updates with the given value.
x- the value
getpublic long 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.
- the current value
resetpublic 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.
getThenResetpublic long getThenReset()Equivalent in effect to
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.
- the value before reset
toStringpublic String toString()Returns the String representation of the current value.
longValuepublic long longValue()
intValuepublic int intValue()
floatValuepublic float floatValue()
doubleValuepublic double doubleValue()