Package com.tnsai.resilience

Class ResilienceMetrics

java.lang.Object

com.tnsai.resilience.ResilienceMetrics

public final class ResilienceMetrics
extends Object

In-memory metrics registry for @Metered actions (issue #173, Phase 1).

Records per-metric-name counters (total, success, failure) and an optional latency histogram. Tests can snapshot any metric via snapshot(java.lang.String); production code reads aggregates via the same API. Phase 2 ships a MetricsSink SPI that lets consumers route the same emissions to Micrometer / Prometheus / OpenTelemetry without changing this class's contract.

Why in-memory in Phase 1

The Phase-1 boundary across this sprint (#171 / #172 / #177 / #173) is "no external storage / no distributed-state SPI". An in-memory registry keyed by metric name is correct for single-instance deployments and safe for tests; multi-node aggregation needs the Phase-2 sink SPI to fan out.

Thread safety

ConcurrentHashMap for the metric map, LongAdder for hot-path counters (better than AtomicLong under contention), ReentrantLock around histogram array mutation. Snapshot reads are point-in-time — concurrent writes during a snapshot are visible-or-not without tearing.

Since:

0.5.4 (issue #173, Phase 1)

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final record	ResilienceMetrics.MetricSnapshot	Immutable snapshot of one metric's state at the moment snapshot(java.lang.String) was called.

Method Summary

Modifier and Type	Method	Description
static ResilienceMetrics	getInstance()	Singleton — Phase 1 has no SPI fan-out, one registry per JVM.
void	record(String name, boolean success, long durationMs, boolean histogram)	Records a single action invocation.
void	resetForTesting()	Test hook — drops every recorded metric.
Optional<ResilienceMetrics.MetricSnapshot>	snapshot(String name)	Snapshots the current state of name, or empty if it was never recorded.
List<ResilienceMetrics.MetricSnapshot>	snapshotAll()	Snapshots every recorded metric.

Methods inherited from class java.lang.Object

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

Method Details

getInstance

public static ResilienceMetrics getInstance()

Singleton — Phase 1 has no SPI fan-out, one registry per JVM.

record

public void record(String name,
 boolean success,
 long durationMs,
 boolean histogram)

Records a single action invocation.

Parameters:

name - the metric name (defaults to class.method when blank)

success - whether the action returned normally

durationMs - measured wall-clock duration in milliseconds

histogram - whether to bucket the duration into the latency histogram (mirrors @Metered.histogram())

snapshot

public Optional<ResilienceMetrics.MetricSnapshot> snapshot(String name)

Snapshots the current state of name, or empty if it was never recorded.

snapshotAll

public List<ResilienceMetrics.MetricSnapshot> snapshotAll()

Snapshots every recorded metric. Order: insertion (per ConcurrentHashMap iteration).

resetForTesting

public void resetForTesting()

Test hook — drops every recorded metric. Production code should never call this; tests use it between cases to prevent cross-test contamination.