Package io.prometheus.metrics.core.metrics

Class SlidingWindow<T>

java.lang.Object

io.prometheus.metrics.core.metrics.SlidingWindow<T>

public class SlidingWindow<T>
extends Object

Maintains a ring buffer of T to implement a sliding time window.

This is used to maintain a sliding window of CKMSQuantiles for Summary metrics.

It is implemented in a generic way so that 3rd party libraries can use it for implementing sliding windows.

Thread Safety: This class uses coarse-grained synchronized methods for simplicity and correctness. All public methods (current() and observe(double)) are synchronized, which ensures thread-safe access to the ring buffer and rotation logic.

Performance Note: The synchronized approach may cause contention under high-frequency observations.

However, given that Summary metrics are less commonly used (Histogram is generally preferred), and the observation frequency is typically lower than Counter increments, the current implementation provides an acceptable trade-off between simplicity and performance.

Field Summary

Fields

Modifier and Type	Field	Description
private final Supplier<T>	constructor
private int	currentBucket
private final LongSupplier	currentTimeMillis
private final long	durationBetweenRotatesMillis
private long	lastRotateTimestampMillis
private final ObjDoubleConsumer<T>	observeFunction
private final T[]	ringBuffer

Constructor Summary

Constructors

Constructor	Description
SlidingWindow(Class<T> clazz, Supplier<T> constructor, ObjDoubleConsumer<T> observeFunction, long maxAgeSeconds, int ageBuckets)	Example: If the maxAgeSeconds is 60 and ageBuckets is 3, then 3 instances of T are maintained and the sliding window moves to the next instance of T every 20 seconds.
SlidingWindow(Class<T> clazz, Supplier<T> constructor, ObjDoubleConsumer<T> observeFunction, long maxAgeSeconds, int ageBuckets, LongSupplier currentTimeMillis)

Method Summary

Modifier and Type	Method	Description
T	current()	Get the currently active instance of T.
void	observe(double value)	Observe a value.
private T	rotate()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

constructor

private final Supplier<T> constructor

observeFunction

private final ObjDoubleConsumer<T> observeFunction

ringBuffer

private final T[] ringBuffer

currentBucket

private int currentBucket

lastRotateTimestampMillis

private long lastRotateTimestampMillis

durationBetweenRotatesMillis

private final long durationBetweenRotatesMillis

currentTimeMillis

private final LongSupplier currentTimeMillis

Constructor Details

SlidingWindow

public SlidingWindow(Class<T> clazz,
 Supplier<T> constructor,
 ObjDoubleConsumer<T> observeFunction,
 long maxAgeSeconds,
 int ageBuckets)

Example: If the maxAgeSeconds is 60 and ageBuckets is 3, then 3 instances of T are maintained and the sliding window moves to the next instance of T every 20 seconds.

Parameters:

clazz - type of T

constructor - for creating a new instance of T as the old one gets evicted

observeFunction - for observing a value (e.g. calling t.observe(value)

maxAgeSeconds - after this amount of time an instance of T gets evicted.

ageBuckets - number of age buckets.

SlidingWindow

SlidingWindow(Class<T> clazz,
 Supplier<T> constructor,
 ObjDoubleConsumer<T> observeFunction,
 long maxAgeSeconds,
 int ageBuckets,
 LongSupplier currentTimeMillis)

Method Details

current

public T current()

Get the currently active instance of T.

observe

public void observe(double value)

Observe a value.

rotate

private T rotate()