Package io.prometheus.client
Class DoubleAdder
java.lang.Object
java.lang.Number
io.prometheus.client.Striped64
io.prometheus.client.DoubleAdder
- All Implemented Interfaces:
Serializable
One or more variables that together maintain an initially zero
double
sum. When updates (method add(double)
) are
contended across threads, the set of variables may grow dynamically
to reduce contention. Method sum()
(or, equivalently doubleValue()
) returns the current total combined across the
variables maintaining the sum.
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.
jsr166e note: This class is targeted to be placed in java.util.concurrent.atomic.
- Since:
- 1.8
- See Also:
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Nested Class Summary
Nested classes/interfaces inherited from class io.prometheus.client.Striped64
Striped64.Cell
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Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
add
(double x) Adds the given value.double
Equivalent tosum()
.float
Returns thesum()
as afloat
after a narrowing primitive conversion.(package private) final long
fn
(long v, long x) Update function.int
intValue()
Returns thesum()
as anint
after a narrowing primitive conversion.long
Returns thesum()
as along
after a narrowing primitive conversion.private void
void
reset()
Resets variables maintaining the sum to zero.void
set
(double x) double
sum()
Returns the current sum.double
toString()
Returns the String representation of thesum()
.private void
Methods inherited from class io.prometheus.client.Striped64
casBase, casBusy, internalReset, retryUpdate
Methods inherited from class java.lang.Number
byteValue, shortValue
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Field Details
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serialVersionUID
private static final long serialVersionUID- See Also:
-
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Constructor Details
-
DoubleAdder
public DoubleAdder()Creates a new adder with initial sum of zero.
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Method Details
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fn
final long fn(long v, long x) Update function. Note that we must use "long" for underlying representations, because there is no compareAndSet for double, due to the fact that the bitwise equals used in any CAS implementation is not the same as double-precision equals. However, we use CAS only to detect and alleviate contention, for which bitwise equals works best anyway. In principle, the long/double conversions used here should be essentially free on most platforms since they just re-interpret bits. Similar conversions are used in other methods. -
add
public void add(double x) Adds the given value.- Parameters:
x
- the value to add
-
sum
public double sum()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. Also, because floating-point arithmetic is not strictly associative, the returned result need not be identical to the value that would be obtained in a sequential series of updates to a single variable.- Returns:
- the sum
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reset
public void reset()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. -
set
public void set(double x) -
sumThenReset
public double sumThenReset()Equivalent in effect tosum()
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 sum
-
toString
Returns the String representation of thesum()
. -
doubleValue
public double doubleValue()Equivalent tosum()
.- Specified by:
doubleValue
in classNumber
- Returns:
- the sum
-
longValue
public long longValue()Returns thesum()
as along
after a narrowing primitive conversion. -
intValue
public int intValue()Returns thesum()
as anint
after a narrowing primitive conversion. -
floatValue
public float floatValue()Returns thesum()
as afloat
after a narrowing primitive conversion.- Specified by:
floatValue
in classNumber
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writeObject
- Throws:
IOException
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readObject
- Throws:
IOException
ClassNotFoundException
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