Module io.prometheus.metrics.core

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.

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.

Method Summary

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

Methods inherited from class java.lang.Object

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

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.

Method Details

current

public T current()

Get the currently active instance of T.

observe

public void observe(double value)

Observe a value.