- All Implemented Interfaces:
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.
- Since:
- 1.8
- See Also:
-
Constructor Summary
ConstructorDescriptionLongAccumulator
(LongBinaryOperator accumulatorFunction, long identity) Creates a new instance using the given accumulator function and identity element. -
Method Summary
Modifier and TypeMethodDescriptionvoid
accumulate
(long x) Updates with the given value.double
Returns the current value as adouble
after a widening primitive conversion.float
Returns the current value as afloat
after a widening primitive conversion.long
get()
Returns the current value.long
int
intValue()
Returns the current value as anint
after a narrowing primitive conversion.long
Equivalent toget()
.void
reset()
Resets variables maintaining updates to the identity value.toString()
Returns the String representation of the current value.Methods declared in class java.lang.Number
byteValue, shortValue
-
Constructor Details
-
LongAccumulator
Creates a new instance using the given accumulator function and identity element.- Parameters:
accumulatorFunction
- a side-effect-free function of two argumentsidentity
- identity (initial value) for the accumulator function
-
-
Method Details
-
accumulate
public void accumulate(long x) Updates with the given value.- Parameters:
x
- the value
-
get
public 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.- 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 long getThenReset()Equivalent in effect toget()
followed byreset()
. 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
-
longValue
-
intValue
public int intValue()Returns the current value as anint
after a narrowing primitive conversion. -
floatValue
public float floatValue()Returns the current value as afloat
after a widening primitive conversion.- Specified by:
floatValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion
to type
float
.
-
doubleValue
public double doubleValue()Returns the current value as adouble
after a widening primitive conversion.- Specified by:
doubleValue
in classNumber
- Returns:
- the numeric value represented by this object after conversion
to type
double
.
-