Package io.github.resilience4j.core.metrics

Class LockFreeFixedSizeSlidingWindowMetrics

java.lang.Object

io.github.resilience4j.core.metrics.LockFreeFixedSizeSlidingWindowMetrics

All Implemented Interfaces:

Metrics

public class LockFreeFixedSizeSlidingWindowMetrics
extends Object
implements Metrics

Implements a lock-free sliding window using a single linked list, represented by a head and a tail reference.

The idea is to initialize the list to the window size, where node N represents the stats for the N-th entry. Besides the stats for the N-th entry, it also contains the stats for the whole window, which are carried over on each new added entry.

When a new record is added, the size of the window is maintained:

1. A new node is added at the tail of the list.
2. The head of the list is moved to the next node.
3. The tail of the list is moved to the next node.

As these operations need to happen atomically, we use the VarHandle API to perform CAS operations on the head, tail and next references. However, these updates are not atomically happening across these references, so we can end up that each reference is updated by a different thread.

The algorithm is based on the following conditions:

• if there is no next node -> try to add one
• else, if the head and tail represent the same N-th stats -> advance the head
• else -> advance the tail

All these operations are done via compare-and-swap operations.

Nested Class Summary

Nested classes/interfaces inherited from interface io.github.resilience4j.core.metrics.Metrics

Metrics.Outcome

Constructor Summary

Constructors

Constructor	Description
LockFreeFixedSizeSlidingWindowMetrics(int windowSize)

Method Summary

Modifier and Type	Method	Description
Snapshot	getSnapshot()	Returns a snapshot.
Snapshot	record(long duration, TimeUnit durationUnit, Metrics.Outcome outcome)	Records a call.

Methods inherited from class java.lang.Object

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

Constructor Details

LockFreeFixedSizeSlidingWindowMetrics

public LockFreeFixedSizeSlidingWindowMetrics(int windowSize)

Method Details

record

public Snapshot record(long duration,
 TimeUnit durationUnit,
 Metrics.Outcome outcome)

Description copied from interface: Metrics

Records a call.

Specified by:

record in interface Metrics

Parameters:

duration - the duration of the call

durationUnit - the time unit of the duration

outcome - the outcome of the call

getSnapshot

public Snapshot getSnapshot()

Description copied from interface: Metrics

Returns a snapshot.

Specified by:

getSnapshot in interface Metrics

Returns:

a snapshot