! all: refactor the core metric recording instruments and accomodate UserMetrics

This PR is including several changes to the kamon-core, most notably:
  - Formalize the interface for Histograms, Counters and MinMaxCounters. Making sure
    that the interfaces are as clean as possible.
  - Move away from the all Vector[Measurement] based Histogram snapshot to a new approach
    in which we use a single long to store both the index in the counts array and the
    frequency on that bucket. The leftmost 2 bytes of each long are used for storing the
    counts array index and the remaining 6 bytes are used for the actual count, and
    everything is put into a simple long array. This way only the buckets that actually
    have values will be included in the snapshot with the smallest possible memory
    footprint.
  - Introduce Gauges.
  - Reorganize the instrumentation for Akka and Scala and rewrite most of the tests
    of this components to avoid going through the subscription protocol to test.
  - Introduce trace tests and fixes on various tests.
  - Necessary changes on new relic, datadog and statsd modules to compile with the new
    codebase.

Pending:
  - Finish the upgrade of the new relic to the current model.
  - Introduce proper limit checks for histograms to ensure that we never pass the 2/6 bytes
    limits.
  - More testing, more testing, more testing.
  - Create the KamonStandalone module.

1 files changed, 110 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/MetricsExtension.scala b/kamon-core/src/main/scala/kamon/metric/MetricsExtension.scala
new file mode 100644
index 00000000..1025f0de
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/MetricsExtension.scala
@@ -0,0 +1,110 @@
+/*
+ * =========================================================================================
+ * 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 java.nio.{ LongBuffer, ByteBuffer }
+
+import scala.collection.concurrent.TrieMap
+import akka.actor._
+import com.typesafe.config.Config
+import kamon.util.GlobPathFilter
+import kamon.Kamon
+import akka.actor
+import kamon.metric.Metrics.MetricGroupFilter
+import kamon.metric.Subscriptions.Subscribe
+import java.util.concurrent.TimeUnit
+
+class MetricsExtension(system: ExtendedActorSystem) extends Kamon.Extension {
+  val metricsExtConfig = system.settings.config.getConfig("kamon.metrics")
+
+  /** Configured Dispatchers */
+  val metricSubscriptionsDispatcher = system.dispatchers.lookup(metricsExtConfig.getString("dispatchers.metric-subscriptions"))
+  val gaugeRecordingsDispatcher = system.dispatchers.lookup(metricsExtConfig.getString("dispatchers.gauge-recordings"))
+
+  /** Configuration Settings */
+  val gaugeRecordingInterval = metricsExtConfig.getDuration("gauge-recording-interval", TimeUnit.MILLISECONDS)
+
+  val storage = TrieMap[MetricGroupIdentity, MetricGroupRecorder]()
+  val filters = loadFilters(metricsExtConfig)
+  lazy val subscriptions = system.actorOf(Props[Subscriptions], "kamon-metrics-subscriptions")
+
+  def register(identity: MetricGroupIdentity, factory: MetricGroupFactory): Option[factory.GroupRecorder] = {
+    if (shouldTrack(identity))
+      Some(storage.getOrElseUpdate(identity, factory.create(metricsExtConfig, system)).asInstanceOf[factory.GroupRecorder])
+    else
+      None
+  }
+
+  def unregister(identity: MetricGroupIdentity): Unit = {
+    storage.remove(identity)
+  }
+
+  def subscribe[C <: MetricGroupCategory](category: C, selection: String, receiver: ActorRef, permanently: Boolean = false): Unit = {
+    subscriptions.tell(Subscribe(category, selection, permanently), receiver)
+  }
+
+  def collect: Map[MetricGroupIdentity, MetricGroupSnapshot] = {
+    // TODO: Improve the way in which we are getting the context.
+    val context = new CollectionContext {
+      val buffer: LongBuffer = LongBuffer.allocate(50000)
+    }
+    (for ((identity, recorder) ← storage) yield (identity, recorder.collect(context))).toMap
+  }
+
+  def scheduleGaugeRecorder(body: ⇒ Unit): Cancellable = {
+    import scala.concurrent.duration._
+
+    system.scheduler.schedule(gaugeRecordingInterval milliseconds, gaugeRecordingInterval milliseconds) {
+      body
+    }(gaugeRecordingsDispatcher)
+  }
+
+  private def shouldTrack(identity: MetricGroupIdentity): Boolean = {
+    filters.get(identity.category.name).map(filter ⇒ filter.accept(identity.name)).getOrElse(true)
+  }
+
+  def loadFilters(config: Config): Map[String, MetricGroupFilter] = {
+    import scala.collection.JavaConverters._
+
+    val filters = config.getObjectList("filters").asScala
+
+    val allFilters =
+      for (
+        filter ← filters;
+        entry ← filter.entrySet().asScala
+      ) yield {
+        val key = entry.getKey
+        val keyBasedConfig = entry.getValue.atKey(key)
+
+        val includes = keyBasedConfig.getStringList(s"$key.includes").asScala.map(inc ⇒ new GlobPathFilter(inc)).toList
+        val excludes = keyBasedConfig.getStringList(s"$key.excludes").asScala.map(exc ⇒ new GlobPathFilter(exc)).toList
+
+        (key, MetricGroupFilter(includes, excludes))
+      }
+
+    allFilters.toMap
+  }
+}
+
+object Metrics extends ExtensionId[MetricsExtension] with ExtensionIdProvider {
+  def lookup(): ExtensionId[_ <: actor.Extension] = Metrics
+  def createExtension(system: ExtendedActorSystem): MetricsExtension = new MetricsExtension(system)
+
+  case class MetricGroupFilter(includes: List[GlobPathFilter], excludes: List[GlobPathFilter]) {
+    def accept(name: String): Boolean = includes.exists(_.accept(name)) && !excludes.exists(_.accept(name))
+  }
+}