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diff --git a/kamon-core/src/main/scala/kamon/metric/MetricsModule.scala b/kamon-core/src/main/scala/kamon/metric/MetricsModule.scala
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+/*
+ * =========================================================================================
+ * Copyright © 2013 the kamon project <http://kamon.io/>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ * =========================================================================================
+ */
+
+package kamon.metric
+
+import akka.actor._
+import com.typesafe.config.Config
+import kamon.metric.SubscriptionsDispatcher.{ Subscribe, Unsubscribe }
+import kamon.metric.instrument.Gauge.CurrentValueCollector
+import kamon.metric.instrument.Histogram.DynamicRange
+import kamon.metric.instrument._
+import kamon.util.LazyActorRef
+
+import scala.collection.concurrent.TrieMap
+import scala.concurrent.duration.FiniteDuration
+
+case class EntityRegistration[T <: EntityRecorder](entity: Entity, recorder: T)
+
+trait MetricsModule {
+  def settings: MetricsSettings
+
+  def shouldTrack(entity: Entity): Boolean
+
+  def shouldTrack(entityName: String, category: String): Boolean =
+    shouldTrack(Entity(entityName, category))
+
+  //
+  // Histograms registration and removal
+  //
+
+  def histogram(name: String): Histogram =
+    registerHistogram(name)
+
+  def histogram(name: String, unitOfMeasurement: UnitOfMeasurement): Histogram =
+    registerHistogram(name, unitOfMeasurement = Some(unitOfMeasurement))
+
+  def histogram(name: String, dynamicRange: DynamicRange): Histogram =
+    registerHistogram(name, dynamicRange = Some(dynamicRange))
+
+  def histogram(name: String, unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange): Histogram =
+    registerHistogram(name, unitOfMeasurement = Some(unitOfMeasurement), dynamicRange = Some(dynamicRange))
+
+  def histogram(name: String, tags: Map[String, String]): Histogram =
+    registerHistogram(name, tags)
+
+  def histogram(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement): Histogram =
+    registerHistogram(name, tags, Some(unitOfMeasurement))
+
+  def histogram(name: String, tags: Map[String, String], dynamicRange: DynamicRange): Histogram =
+    registerHistogram(name, tags, dynamicRange = Some(dynamicRange))
+
+  def histogram(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange): Histogram =
+    registerHistogram(name, tags, Some(unitOfMeasurement), Some(dynamicRange))
+
+  def removeHistogram(name: String): Boolean =
+    removeHistogram(name, Map.empty)
+
+  def registerHistogram(name: String, tags: Map[String, String] = Map.empty, unitOfMeasurement: Option[UnitOfMeasurement] = None,
+    dynamicRange: Option[DynamicRange] = None): Histogram
+
+  def removeHistogram(name: String, tags: Map[String, String]): Boolean
+
+  //
+  // MinMaxCounter registration and removal
+  //
+
+  def minMaxCounter(name: String): MinMaxCounter =
+    registerMinMaxCounter(name)
+
+  def minMaxCounter(name: String, unitOfMeasurement: UnitOfMeasurement): MinMaxCounter =
+    registerMinMaxCounter(name, unitOfMeasurement = Some(unitOfMeasurement))
+
+  def minMaxCounter(name: String, dynamicRange: DynamicRange): MinMaxCounter =
+    registerMinMaxCounter(name, dynamicRange = Some(dynamicRange))
+
+  def minMaxCounter(name: String, refreshInterval: FiniteDuration): MinMaxCounter =
+    registerMinMaxCounter(name, refreshInterval = Some(refreshInterval))
+
+  def minMaxCounter(name: String, dynamicRange: DynamicRange, refreshInterval: FiniteDuration): MinMaxCounter =
+    registerMinMaxCounter(name, dynamicRange = Some(dynamicRange), refreshInterval = Some(refreshInterval))
+
+  def minMaxCounter(name: String, unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange): MinMaxCounter =
+    registerMinMaxCounter(name, unitOfMeasurement = Some(unitOfMeasurement), dynamicRange = Some(dynamicRange))
+
+  def minMaxCounter(name: String, tags: Map[String, String]): MinMaxCounter =
+    registerMinMaxCounter(name, tags)
+
+  def minMaxCounter(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement): MinMaxCounter =
+    registerMinMaxCounter(name, tags, Some(unitOfMeasurement))
+
+  def minMaxCounter(name: String, tags: Map[String, String], dynamicRange: DynamicRange): MinMaxCounter =
+    registerMinMaxCounter(name, tags, dynamicRange = Some(dynamicRange))
+
+  def minMaxCounter(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange): MinMaxCounter =
+    registerMinMaxCounter(name, tags, Some(unitOfMeasurement), Some(dynamicRange))
+
+  def removeMinMaxCounter(name: String): Boolean =
+    removeMinMaxCounter(name, Map.empty)
+
+  def removeMinMaxCounter(name: String, tags: Map[String, String]): Boolean
+
+  def registerMinMaxCounter(name: String, tags: Map[String, String] = Map.empty, unitOfMeasurement: Option[UnitOfMeasurement] = None,
+    dynamicRange: Option[DynamicRange] = None, refreshInterval: Option[FiniteDuration] = None): MinMaxCounter
+
+  //
+  // Gauge registration and removal
+  //
+
+  def gauge(name: String)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector)
+
+  def gauge(name: String, unitOfMeasurement: UnitOfMeasurement)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, unitOfMeasurement = Some(unitOfMeasurement))
+
+  def gauge(name: String, dynamicRange: DynamicRange)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, dynamicRange = Some(dynamicRange))
+
+  def gauge(name: String, refreshInterval: FiniteDuration)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, refreshInterval = Some(refreshInterval))
+
+  def gauge(name: String, dynamicRange: DynamicRange, refreshInterval: FiniteDuration)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, dynamicRange = Some(dynamicRange), refreshInterval = Some(refreshInterval))
+
+  def gauge(name: String, unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, unitOfMeasurement = Some(unitOfMeasurement), dynamicRange = Some(dynamicRange))
+
+  def gauge(name: String, tags: Map[String, String])(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, tags)
+
+  def gauge(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, tags, Some(unitOfMeasurement))
+
+  def gauge(name: String, tags: Map[String, String], dynamicRange: DynamicRange)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, tags, dynamicRange = Some(dynamicRange))
+
+  def gauge(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement, dynamicRange: DynamicRange)(valueCollector: CurrentValueCollector): Gauge =
+    registerGauge(name, valueCollector, tags, Some(unitOfMeasurement), Some(dynamicRange))
+
+  def removeGauge(name: String): Boolean =
+    removeGauge(name, Map.empty)
+
+  def removeGauge(name: String, tags: Map[String, String]): Boolean
+
+  def registerGauge(name: String, valueCollector: CurrentValueCollector, tags: Map[String, String] = Map.empty,
+    unitOfMeasurement: Option[UnitOfMeasurement] = None, dynamicRange: Option[DynamicRange] = None,
+    refreshInterval: Option[FiniteDuration] = None): Gauge
+
+  //
+  // Counters registration and removal
+  //
+
+  def counter(name: String): Counter =
+    registerCounter(name)
+
+  def counter(name: String, unitOfMeasurement: UnitOfMeasurement): Counter =
+    registerCounter(name, unitOfMeasurement = Some(unitOfMeasurement))
+
+  def counter(name: String, tags: Map[String, String]): Counter =
+    registerCounter(name, tags)
+
+  def counter(name: String, tags: Map[String, String], unitOfMeasurement: UnitOfMeasurement): Counter =
+    registerCounter(name, tags, Some(unitOfMeasurement))
+
+  def removeCounter(name: String): Boolean =
+    removeCounter(name, Map.empty)
+
+  def removeCounter(name: String, tags: Map[String, String]): Boolean
+
+  def registerCounter(name: String, tags: Map[String, String] = Map.empty, unitOfMeasurement: Option[UnitOfMeasurement] = None,
+    dynamicRange: Option[DynamicRange] = None): Counter
+
+  //
+  // Entities registration and removal
+  //
+
+  def entity[T <: EntityRecorder](recorderFactory: EntityRecorderFactory[T], name: String): T =
+    entity(recorderFactory, Entity(name, recorderFactory.category))
+
+  def entity[T <: EntityRecorder](recorderFactory: EntityRecorderFactory[T], name: String, tags: Map[String, String]): T =
+    entity(recorderFactory, Entity(name, recorderFactory.category, tags))
+
+  def removeEntity(name: String, category: String): Boolean =
+    removeEntity(Entity(name, category, Map.empty))
+
+  def removeEntity(name: String, category: String, tags: Map[String, String]): Boolean =
+    removeEntity(Entity(name, category, tags))
+
+  def removeEntity(entity: Entity): Boolean
+
+  def entity[T <: EntityRecorder](recorderFactory: EntityRecorderFactory[T], entity: Entity): T
+
+  def find(name: String, category: String): Option[EntityRecorder] =
+    find(Entity(name, category))
+
+  def find(name: String, category: String, tags: Map[String, String]): Option[EntityRecorder] =
+    find(Entity(name, category, tags))
+
+  def find(entity: Entity): Option[EntityRecorder]
+
+  def subscribe(filter: SubscriptionFilter, subscriber: ActorRef): Unit =
+    subscribe(filter, subscriber, permanently = true)
+
+  def subscribe(category: String, selection: String, subscriber: ActorRef, permanently: Boolean): Unit =
+    subscribe(SubscriptionFilter(category, selection), subscriber, permanently)
+
+  def subscribe(category: String, selection: String, subscriber: ActorRef): Unit =
+    subscribe(SubscriptionFilter(category, selection), subscriber, permanently = true)
+
+  def subscribe(filter: SubscriptionFilter, subscriber: ActorRef, permanently: Boolean): Unit
+
+  def unsubscribe(subscriber: ActorRef): Unit
+
+  def buildDefaultCollectionContext: CollectionContext
+
+  def instrumentFactory(category: String): InstrumentFactory
+}
+
+private[kamon] class MetricsModuleImpl(config: Config) extends MetricsModule {
+  import kamon.util.TriemapAtomicGetOrElseUpdate.Syntax
+
+  private val _trackedEntities = TrieMap.empty[Entity, EntityRecorder]
+  private val _subscriptions = new LazyActorRef
+
+  val settings = MetricsSettings(config)
+
+  def shouldTrack(entity: Entity): Boolean =
+    settings.entityFilters.get(entity.category).map {
+      filter ⇒ filter.accept(entity.name)
+
+    } getOrElse (settings.trackUnmatchedEntities)
+
+  def registerHistogram(name: String, tags: Map[String, String], unitOfMeasurement: Option[UnitOfMeasurement],
+    dynamicRange: Option[DynamicRange]): Histogram = {
+
+    val histogramEntity = Entity(name, SingleInstrumentEntityRecorder.Histogram, tags)
+    val recorder = _trackedEntities.atomicGetOrElseUpdate(histogramEntity, {
+      val factory = instrumentFactory(histogramEntity.category)
+      HistogramRecorder(HistogramKey(histogramEntity.category, unitOfMeasurement.getOrElse(UnitOfMeasurement.Unknown)),
+        factory.createHistogram(name, dynamicRange))
+    }, _.cleanup)
+
+    recorder.asInstanceOf[HistogramRecorder].instrument
+  }
+
+  def removeHistogram(name: String, tags: Map[String, String]): Boolean =
+    _trackedEntities.remove(Entity(name, SingleInstrumentEntityRecorder.Histogram, tags)).isDefined
+
+  def registerMinMaxCounter(name: String, tags: Map[String, String], unitOfMeasurement: Option[UnitOfMeasurement], dynamicRange: Option[DynamicRange],
+    refreshInterval: Option[FiniteDuration]): MinMaxCounter = {
+
+    val minMaxCounterEntity = Entity(name, SingleInstrumentEntityRecorder.MinMaxCounter, tags)
+    val recorder = _trackedEntities.atomicGetOrElseUpdate(minMaxCounterEntity, {
+      val factory = instrumentFactory(minMaxCounterEntity.category)
+      MinMaxCounterRecorder(MinMaxCounterKey(minMaxCounterEntity.category, unitOfMeasurement.getOrElse(UnitOfMeasurement.Unknown)),
+        factory.createMinMaxCounter(name, dynamicRange, refreshInterval))
+    }, _.cleanup)
+
+    recorder.asInstanceOf[MinMaxCounterRecorder].instrument
+  }
+
+  def removeMinMaxCounter(name: String, tags: Map[String, String]): Boolean =
+    _trackedEntities.remove(Entity(name, SingleInstrumentEntityRecorder.MinMaxCounter, tags)).isDefined
+
+  def registerGauge(name: String, valueCollector: CurrentValueCollector, tags: Map[String, String] = Map.empty,
+    unitOfMeasurement: Option[UnitOfMeasurement] = None, dynamicRange: Option[DynamicRange] = None,
+    refreshInterval: Option[FiniteDuration] = None): Gauge = {
+
+    val gaugeEntity = Entity(name, SingleInstrumentEntityRecorder.Gauge, tags)
+    val recorder = _trackedEntities.atomicGetOrElseUpdate(gaugeEntity, {
+      val factory = instrumentFactory(gaugeEntity.category)
+      GaugeRecorder(MinMaxCounterKey(gaugeEntity.category, unitOfMeasurement.getOrElse(UnitOfMeasurement.Unknown)),
+        factory.createGauge(name, dynamicRange, refreshInterval, valueCollector))
+    }, _.cleanup)
+
+    recorder.asInstanceOf[GaugeRecorder].instrument
+  }
+
+  def removeGauge(name: String, tags: Map[String, String]): Boolean =
+    _trackedEntities.remove(Entity(name, SingleInstrumentEntityRecorder.Gauge, tags)).isDefined
+
+  def registerCounter(name: String, tags: Map[String, String] = Map.empty, unitOfMeasurement: Option[UnitOfMeasurement] = None,
+    dynamicRange: Option[DynamicRange] = None): Counter = {
+
+    val counterEntity = Entity(name, SingleInstrumentEntityRecorder.Counter, tags)
+    val recorder = _trackedEntities.atomicGetOrElseUpdate(counterEntity, {
+      val factory = instrumentFactory(counterEntity.category)
+      CounterRecorder(CounterKey(counterEntity.category, unitOfMeasurement.getOrElse(UnitOfMeasurement.Unknown)),
+        factory.createCounter())
+    }, _.cleanup)
+
+    recorder.asInstanceOf[CounterRecorder].instrument
+  }
+
+  def removeCounter(name: String, tags: Map[String, String]): Boolean =
+    _trackedEntities.remove(Entity(name, SingleInstrumentEntityRecorder.Counter, tags)).isDefined
+
+  def entity[T <: EntityRecorder](recorderFactory: EntityRecorderFactory[T], entity: Entity): T = {
+    _trackedEntities.atomicGetOrElseUpdate(entity, {
+      recorderFactory.createRecorder(instrumentFactory(recorderFactory.category))
+    }, _.cleanup).asInstanceOf[T]
+  }
+
+  def removeEntity(entity: Entity): Boolean =
+    _trackedEntities.remove(entity).isDefined
+
+  def find(entity: Entity): Option[EntityRecorder] =
+    _trackedEntities.get(entity)
+
+  def subscribe(filter: SubscriptionFilter, subscriber: ActorRef, permanent: Boolean): Unit =
+    _subscriptions.tell(Subscribe(filter, subscriber, permanent))
+
+  def unsubscribe(subscriber: ActorRef): Unit =
+    _subscriptions.tell(Unsubscribe(subscriber))
+
+  def buildDefaultCollectionContext: CollectionContext =
+    CollectionContext(settings.defaultCollectionContextBufferSize)
+
+  def instrumentFactory(category: String): InstrumentFactory =
+    settings.instrumentFactories.getOrElse(category, settings.defaultInstrumentFactory)
+
+  private[kamon] def collectSnapshots(collectionContext: CollectionContext): Map[Entity, EntitySnapshot] = {
+    val builder = Map.newBuilder[Entity, EntitySnapshot]
+    _trackedEntities.foreach {
+      case (identity, recorder) ⇒ builder += ((identity, recorder.collect(collectionContext)))
+    }
+
+    builder.result()
+  }
+
+  /**
+   *  Metrics Extension initialization.
+   */
+  private var _system: ActorSystem = null
+  private lazy val _start = {
+    _subscriptions.point(_system.actorOf(SubscriptionsDispatcher.props(settings.tickInterval, this), "metrics"))
+    settings.pointScheduler(DefaultRefreshScheduler(_system.scheduler, _system.dispatcher))
+  }
+
+  def start(system: ActorSystem): Unit = synchronized {
+    _system = system
+    _start
+    _system = null
+  }
+}
+
+private[kamon] object MetricsModuleImpl {
+
+  def apply(config: Config) =
+    new MetricsModuleImpl(config)
+}
+