public
class
LongAccumulator
extends Number
implements
Serializable
java.lang.Object | ||
↳ | java.lang.Number | |
↳ | java.util.concurrent.atomic.LongAccumulator |
One or more variables that together maintain a running 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. The function is applied with
the current value as its first argument, and the given update as
the second 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.
Public constructors | |
---|---|
LongAccumulator(LongBinaryOperator accumulatorFunction, long identity)
Creates a new instance using the given accumulator function and identity element. |
Public methods | |
---|---|
void
|
accumulate(long x)
Updates with the given value. |
double
|
doubleValue()
Returns the current value as a |
float
|
floatValue()
Returns the current value as a |
long
|
get()
Returns the current value. |
long
|
getThenReset()
|
int
|
intValue()
Returns the current value as an |
long
|
longValue()
Equivalent to |
void
|
reset()
Resets variables maintaining updates to the identity value. |
String
|
toString()
Returns the String representation of the current value. |
Inherited methods | |
---|---|
From
class
java.lang.Number
| |
From
class
java.lang.Object
|
LongAccumulator (LongBinaryOperator accumulatorFunction, long identity)
Creates a new instance using the given accumulator function and identity element.
Parameters | |
---|---|
accumulatorFunction |
LongBinaryOperator :
a side-effect-free function of two arguments |
identity |
long :
identity (initial value) for the accumulator function
|
void accumulate (long x)
Updates with the given value.
Parameters | |
---|---|
x |
long :
the value
|
double doubleValue ()
Returns the current value as a double
after a widening primitive conversion.
Returns | |
---|---|
double |
the numeric value represented by this object after conversion
to type double .
|
float floatValue ()
Returns the current value as a float
after a widening primitive conversion.
Returns | |
---|---|
float |
the numeric value represented by this object after conversion
to type float .
|
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 | |
---|---|
long |
the current value |
long 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 | |
---|---|
long |
the value before reset |
int intValue ()
Returns the current value as an int
after a narrowing primitive conversion.
Returns | |
---|---|
int |
the numeric value represented by this object after conversion
to type int .
|
long longValue ()
Equivalent to get()
.
Returns | |
---|---|
long |
the current value |
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.
String toString ()
Returns the String representation of the current value.
Returns | |
---|---|
String |
the String representation of the current value |