Avoid capturing lambda allocation when retrieving existing meters

shakuzen · shakuzen · commit 68327bb85f6d · 2025-08-27T17:43:04.000+09:00
In particular focuses on Timer, LongTaskTimer, and Counter as these are the types expected to be retrieved (non-functional) the most.
Avoiding this allocation makes the retrieval more performant and generates less garbage, causing less GC pressure.
diff --git a/benchmarks/benchmarks-core/src/jmh/java/io/micrometer/benchmark/core/MeterRegistrationBenchmark.java b/benchmarks/benchmarks-core/src/jmh/java/io/micrometer/benchmark/core/MeterRegistrationBenchmark.java
@@ -33,7 +33,7 @@
 @Warmup(iterations = 2)
 @Measurement(iterations = 5)
 @BenchmarkMode(Mode.AverageTime)
-@OutputTimeUnit(TimeUnit.MICROSECONDS)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
 @Threads(2)
 public class MeterRegistrationBenchmark {
 
@@ -49,7 +49,7 @@ public static void main(String[] args) throws RunnerException {
 
     Meter.MeterProvider<Counter> counterMeterProvider = Counter.builder("jmh.existing").withRegistry(registry);
 
-    Tags tags = Tags.of("key", "value");
+    Tags tags = Tags.of("k1", "v1");
 
     @Setup
     public void setup() {
@@ -89,8 +89,8 @@ public Meter registerStale() {
     }
 
     @Benchmark
-    public Meter registerExisting() {
-        return registry.counter("jmh.existing", "k1", "v1");
+    public Meter registerExistingCounter() {
+        return registry.counter("jmh.existing", tags);
     }
 
     @Benchmark
diff --git a/benchmarks/benchmarks-core/src/jmh/java/io/micrometer/benchmark/core/ObservationBenchmark.java b/benchmarks/benchmarks-core/src/jmh/java/io/micrometer/benchmark/core/ObservationBenchmark.java
@@ -80,11 +80,11 @@ public boolean supportsContext(Observation.Context context) {
         };
     }
 
-    @TearDown
-    public void tearDown() {
-        System.out.println("Meters:");
-        System.out.println(meterRegistry.getMetersAsString());
-    }
+    // @TearDown
+    // public void tearDown() {
+    // System.out.println("Meters:");
+    // System.out.println(meterRegistry.getMetersAsString());
+    // }
 
     @Benchmark
     public void baseline() {
diff --git a/implementations/micrometer-registry-dynatrace/src/test/java/io/micrometer/dynatrace/types/DynatraceTimerTest.java b/implementations/micrometer-registry-dynatrace/src/test/java/io/micrometer/dynatrace/types/DynatraceTimerTest.java
@@ -47,7 +47,7 @@ class DynatraceTimerTest {
 
     private static final DistributionStatisticConfig DISTRIBUTION_STATISTIC_CONFIG = DistributionStatisticConfig.NONE;
 
-    private static final PauseDetector PAUSE_DETECTOR = new NoPauseDetector();
+    private static final PauseDetector PAUSE_DETECTOR = NoPauseDetector.INSTANCE;
 
     @Test
     void testTimerCount() {
diff --git a/micrometer-core/src/main/java/io/micrometer/core/instrument/MeterRegistry.java b/micrometer-core/src/main/java/io/micrometer/core/instrument/MeterRegistry.java
@@ -31,6 +31,8 @@
 import io.micrometer.core.instrument.search.RequiredSearch;
 import io.micrometer.core.instrument.search.Search;
 import io.micrometer.core.instrument.util.TimeUtils;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.NullUnmarked;
 import org.jspecify.annotations.Nullable;
 
 import java.time.Duration;
@@ -106,7 +108,7 @@ public abstract class MeterRegistry {
 
     /**
      * write/remove guarded by meterMapLock, read in
-     * {@link #getOrCreateMeter(DistributionStatisticConfig, BiFunction, Meter.Id, Function)}
+     * {@link #getOrCreateMeter(DistributionStatisticConfig, PauseDetector, NewMeterSupplier, Meter.Id, Function)}
      * is unguarded
      */
     private final Map<Meter.Id, Meter> preFilterIdToMeterMap = new HashMap<>();
@@ -135,7 +137,7 @@ public abstract class MeterRegistry {
 
     private final AtomicBoolean closed = new AtomicBoolean();
 
-    private PauseDetector pauseDetector = new NoPauseDetector();
+    private PauseDetector pauseDetector = NoPauseDetector.INSTANCE;
 
     private @Nullable HighCardinalityTagsDetector highCardinalityTagsDetector;
 
@@ -338,9 +340,12 @@ private String getBaseTimeUnitStr() {
      * Only used by {@link Counter#builder(String)}.
      * @param id The identifier for this counter.
      * @return A new or existing counter.
+     * @implNote Avoids allocation in the case the meter is already registered,
+     * particularly capturing lambdas.
      */
     Counter counter(Meter.Id id) {
-        return registerMeterIfNecessary(Counter.class, id, this::newCounter, NoopCounter::new);
+        return registerMeterIfNecessary(Counter.class, id, null, null,
+                (registry, mappedId, mappedConfig, pd) -> registry.newCounter(mappedId), NoopCounter::new);
     }
 
     /**
@@ -352,22 +357,27 @@ Counter counter(Meter.Id id) {
      * @return A new or existing gauge.
      */
     <T> Gauge gauge(Meter.Id id, @Nullable T obj, ToDoubleFunction<T> valueFunction) {
-        return registerMeterIfNecessary(Gauge.class, id, id2 -> newGauge(id2, obj, valueFunction), NoopGauge::new);
+        return registerMeterIfNecessary(Gauge.class, id,
+                (registry, mappedId) -> registry.newGauge(mappedId, obj, valueFunction), NoopGauge::new);
     }
 
     /**
-     * Only used by {@link Timer#builder(String)}.
+     * Only used internally.
      * @param id The identifier for this timer.
      * @param distributionStatisticConfig Configuration that governs how distribution
      * statistics are computed.
+     * @param specificPauseDetector explicit pause detector to use that may be different
+     * from the registry-configured one
      * @return A new or existing timer.
+     * @implNote Avoids allocation in the case the meter is already registered,
+     * particularly capturing lambdas.
      */
     Timer timer(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig,
-            PauseDetector pauseDetectorOverride) {
-        return registerMeterIfNecessary(Timer.class, id, distributionStatisticConfig, (id2, filteredConfig) -> {
-            Meter.Id withUnit = id2.withBaseUnit(getBaseTimeUnitStr());
-            return newTimer(withUnit, filteredConfig.merge(defaultHistogramConfig()), pauseDetectorOverride);
-        }, NoopTimer::new);
+            PauseDetector specificPauseDetector) {
+        return registerMeterIfNecessary(Timer.class, id, distributionStatisticConfig, specificPauseDetector,
+                (registry, mappedId, mappedConfig, pd) -> registry
+                    .newTimer(mappedId.withBaseUnit(registry.getBaseTimeUnitStr()), mappedConfig, pd),
+                NoopTimer::new);
     }
 
     /**
@@ -378,8 +388,9 @@ Timer timer(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig
      * @return A new or existing distribution summary.
      */
     DistributionSummary summary(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig, double scale) {
-        return registerMeterIfNecessary(DistributionSummary.class, id, distributionStatisticConfig, (id2,
-                filteredConfig) -> newDistributionSummary(id2, filteredConfig.merge(defaultHistogramConfig()), scale),
+        return registerMeterIfNecessary(
+                DistributionSummary.class, id, distributionStatisticConfig, null, (registry, mappedId, filteredConfig,
+                        pd) -> registry.newDistributionSummary(mappedId, filteredConfig, scale),
                 NoopDistributionSummary::new);
     }
 
@@ -392,7 +403,8 @@ DistributionSummary summary(Meter.Id id, DistributionStatisticConfig distributio
      * @return The meter.
      */
     Meter register(Meter.Id id, Meter.Type type, Iterable<Measurement> measurements) {
-        return registerMeterIfNecessary(Meter.class, id, id2 -> newMeter(id2, type, measurements), NoopMeter::new);
+        return registerMeterIfNecessary(Meter.class, id,
+                (registry, mappedId) -> registry.newMeter(mappedId, type, measurements), NoopMeter::new);
     }
 
     /**
@@ -607,14 +619,15 @@ public <T extends Collection<?>> T gaugeCollectionSize(String name, Iterable<Tag
     }
 
     private <M extends Meter> M registerMeterIfNecessary(Class<M> meterClass, Meter.Id id,
-            Function<Meter.Id, M> builder, Function<Meter.Id, M> noopBuilder) {
-        return registerMeterIfNecessary(meterClass, id, null, (id2, conf) -> builder.apply(id2), noopBuilder);
+            BiFunction<MeterRegistry, Meter.Id, M> meterSupplier, Function<Meter.Id, M> noopBuilder) {
+        return registerMeterIfNecessary(meterClass, id, null, null,
+                (registry, mappedId, conf, pd) -> meterSupplier.apply(registry, mappedId), noopBuilder);
     }
 
     private <M extends Meter> M registerMeterIfNecessary(Class<M> meterClass, Meter.Id id,
-            @Nullable DistributionStatisticConfig config, BiFunction<Meter.Id, DistributionStatisticConfig, M> builder,
-            Function<Meter.Id, M> noopBuilder) {
-        Meter m = getOrCreateMeter(config, builder, id, noopBuilder);
+            @Nullable DistributionStatisticConfig config, @Nullable PauseDetector specificPauseDetector,
+            NewMeterSupplier<M> meterSupplier, Function<Meter.Id, M> noopBuilder) {
+        Meter m = getOrCreateMeter(config, specificPauseDetector, meterSupplier, id, noopBuilder);
 
         if (!meterClass.isInstance(m)) {
             throw new IllegalArgumentException(
@@ -643,8 +656,29 @@ private Meter.Id mapId(Meter.Id id) {
         return mappedId;
     }
 
+    @FunctionalInterface
+    // Brittle, but this is internal. We pass nulls for some meter types as explained in
+    // JavaDoc.
+    @NullUnmarked
+    private interface NewMeterSupplier<M extends Meter> {
+
+        /**
+         * Create a new meter with the given parameters. The DistributionStatisticConfig
+         * and PauseDetector will be null for meter types that do not take them.
+         * @param registry the registry from which to make the new meter
+         * @param id the ID of the meter to create
+         * @param distributionStatisticConfig optional distribution config for types that
+         * take it
+         * @param pauseDetector optional pause detector for types that take it
+         * @return a new meter
+         */
+        @NonNull M create(MeterRegistry registry, Meter.Id id, DistributionStatisticConfig distributionStatisticConfig,
+                PauseDetector pauseDetector);
+
+    }
+
     private Meter getOrCreateMeter(@Nullable DistributionStatisticConfig config,
-            BiFunction<Meter.Id, /* Nullable Generic */ DistributionStatisticConfig, ? extends Meter> builder,
+            @Nullable PauseDetector specificPauseDetector, NewMeterSupplier<? extends Meter> meterSupplier,
             Meter.Id originalId, Function<Meter.Id, ? extends Meter> noopBuilder) {
 
         Meter m = preFilterIdToMeterMap.get(originalId);
@@ -684,9 +718,10 @@ private Meter getOrCreateMeter(@Nullable DistributionStatisticConfig config,
                                 config = filteredConfig;
                             }
                         }
+                        config = config.merge(defaultHistogramConfig());
                     }
 
-                    m = builder.apply(mappedId, config);
+                    m = meterSupplier.create(this, mappedId, config, specificPauseDetector);
 
                     Meter.Id synAssoc = mappedId.syntheticAssociation();
                     if (synAssoc != null) {
@@ -1066,13 +1101,14 @@ public LongTaskTimer longTaskTimer(String name, Iterable<Tag> tags) {
          * Only used by {@link LongTaskTimer#builder(String)}.
          * @param id The identifier for this long task timer.
          * @return A new or existing long task timer.
+         * @implNote Avoids allocation in the case the meter is already registered,
+         * particularly capturing lambdas.
          */
         LongTaskTimer longTaskTimer(Meter.Id id, DistributionStatisticConfig distributionStatisticConfig) {
-            return registerMeterIfNecessary(LongTaskTimer.class, id, distributionStatisticConfig,
-                    (id2, filteredConfig) -> {
-                        Meter.Id withUnit = id2.withBaseUnit(getBaseTimeUnitStr());
-                        return newLongTaskTimer(withUnit, filteredConfig.merge(defaultHistogramConfig()));
-                    }, NoopLongTaskTimer::new);
+            return registerMeterIfNecessary(LongTaskTimer.class, id, distributionStatisticConfig, null,
+                    (registry, mappedId, mappedConfig, pd) -> registry
+                        .newLongTaskTimer(mappedId.withBaseUnit(registry.getBaseTimeUnitStr()), mappedConfig),
+                    NoopLongTaskTimer::new);
         }
 
         /**
@@ -1116,7 +1152,8 @@ public <T extends Number> FunctionCounter counter(String name, Iterable<Tag> tag
          */
         <T> FunctionCounter counter(Meter.Id id, T obj, ToDoubleFunction<T> countFunction) {
             return registerMeterIfNecessary(FunctionCounter.class, id,
-                    id2 -> newFunctionCounter(id2, obj, countFunction), NoopFunctionCounter::new);
+                    (registry, mappedId) -> registry.newFunctionCounter(mappedId, obj, countFunction),
+                    NoopFunctionCounter::new);
         }
 
         /**
@@ -1157,10 +1194,10 @@ public <T> FunctionTimer timer(String name, Iterable<Tag> tags, T obj, ToLongFun
          */
         <T> FunctionTimer timer(Meter.Id id, T obj, ToLongFunction<T> countFunction,
                 ToDoubleFunction<T> totalTimeFunction, TimeUnit totalTimeFunctionUnit) {
-            return registerMeterIfNecessary(FunctionTimer.class, id, id2 -> {
-                Meter.Id withUnit = id2.withBaseUnit(getBaseTimeUnitStr());
-                return newFunctionTimer(withUnit, obj, countFunction, totalTimeFunction, totalTimeFunctionUnit);
-            }, NoopFunctionTimer::new);
+            return registerMeterIfNecessary(FunctionTimer.class, id,
+                    (registry, mappedId) -> registry.newFunctionTimer(mappedId.withBaseUnit(getBaseTimeUnitStr()), obj,
+                            countFunction, totalTimeFunction, totalTimeFunctionUnit),
+                    NoopFunctionTimer::new);
         }
 
         /**
@@ -1198,7 +1235,8 @@ public <T> TimeGauge timeGauge(String name, Iterable<Tag> tags, T obj, TimeUnit
         <T> TimeGauge timeGauge(Meter.Id id, @Nullable T obj, TimeUnit timeFunctionUnit,
                 ToDoubleFunction<T> timeFunction) {
             return registerMeterIfNecessary(TimeGauge.class, id,
-                    id2 -> newTimeGauge(id2, obj, timeFunctionUnit, timeFunction), NoopTimeGauge::new);
+                    (registry, mappedId) -> registry.newTimeGauge(mappedId, obj, timeFunctionUnit, timeFunction),
+                    NoopTimeGauge::new);
         }
 
     }
diff --git a/micrometer-core/src/main/java/io/micrometer/core/instrument/distribution/pause/NoPauseDetector.java b/micrometer-core/src/main/java/io/micrometer/core/instrument/distribution/pause/NoPauseDetector.java
@@ -15,6 +15,22 @@
  */
 package io.micrometer.core.instrument.distribution.pause;
 
+/**
+ * No-op implementation of a {@link PauseDetector}.
+ */
 public class NoPauseDetector implements PauseDetector {
 
+    /**
+     * Singleton instance of {@link NoPauseDetector}.
+     * @since 1.16.0
+     */
+    public static final NoPauseDetector INSTANCE = new NoPauseDetector();
+
+    /**
+     * @deprecated use {@link #INSTANCE} instead.
+     */
+    @Deprecated
+    public NoPauseDetector() {
+    }
+
 }
diff --git a/micrometer-core/src/test/java/io/micrometer/core/instrument/AbstractTimerTests.java b/micrometer-core/src/test/java/io/micrometer/core/instrument/AbstractTimerTests.java
@@ -75,7 +75,7 @@ static class MyTimer extends AbstractTimer {
 
         MyTimer() {
             super(new Meter.Id("name", Tags.empty(), null, null, Meter.Type.TIMER), Clock.SYSTEM,
-                    DistributionStatisticConfig.DEFAULT, new NoPauseDetector(), TimeUnit.SECONDS, false);
+                    DistributionStatisticConfig.DEFAULT, NoPauseDetector.INSTANCE, TimeUnit.SECONDS, false);
         }
 
         @Override

Original file line number	Diff line number	Diff line change
`@@ -75,7 +75,7 @@ static class MyTimer extends AbstractTimer {`
`75`	`75`
`76`	`76`	`MyTimer() {`
`77`	`77`	`super(new Meter.Id("name", Tags.empty(), null, null, Meter.Type.TIMER), Clock.SYSTEM,`
`78`		`- DistributionStatisticConfig.DEFAULT, new NoPauseDetector(), TimeUnit.SECONDS, false);`
	`78`	`+ DistributionStatisticConfig.DEFAULT, NoPauseDetector.INSTANCE, TimeUnit.SECONDS, false);`
`79`	`79`	`}`
`80`	`80`
`81`	`81`	`@Override`