! 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, 128 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/Subscriptions.scala b/kamon-core/src/main/scala/kamon/metric/Subscriptions.scala
new file mode 100644
index 00000000..a9f4c721
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/Subscriptions.scala
@@ -0,0 +1,128 @@
+/*
+ * =========================================================================================
+ * 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.{ Props, ActorRef, Actor }
+import kamon.metric.Subscriptions.{ MetricGroupFilter, FlushMetrics, TickMetricSnapshot, Subscribe }
+import kamon.util.GlobPathFilter
+import scala.concurrent.duration.{ FiniteDuration, Duration }
+import java.util.concurrent.TimeUnit
+import kamon.Kamon
+import kamon.metric.TickMetricSnapshotBuffer.FlushBuffer
+
+class Subscriptions extends Actor {
+  import context.system
+
+  val config = context.system.settings.config
+  val tickInterval = Duration(config.getDuration("kamon.metrics.tick-interval", TimeUnit.NANOSECONDS), TimeUnit.NANOSECONDS)
+  val flushMetricsSchedule = context.system.scheduler.schedule(tickInterval, tickInterval, self, FlushMetrics)(context.dispatcher)
+
+  var lastTick: Long = System.currentTimeMillis()
+  var subscribedPermanently: Map[MetricGroupFilter, List[ActorRef]] = Map.empty
+  var subscribedForOneShot: Map[MetricGroupFilter, List[ActorRef]] = Map.empty
+
+  def receive = {
+    case Subscribe(category, selection, permanent) ⇒ subscribe(category, selection, permanent)
+    case FlushMetrics                              ⇒ flush()
+  }
+
+  def subscribe(category: MetricGroupCategory, selection: String, permanent: Boolean): Unit = {
+    val filter = MetricGroupFilter(category, new GlobPathFilter(selection))
+    if (permanent) {
+      val receivers = subscribedPermanently.get(filter).getOrElse(Nil)
+      subscribedPermanently = subscribedPermanently.updated(filter, sender :: receivers)
+
+    } else {
+      val receivers = subscribedForOneShot.get(filter).getOrElse(Nil)
+      subscribedForOneShot = subscribedForOneShot.updated(filter, sender :: receivers)
+    }
+
+  }
+
+  def flush(): Unit = {
+    val currentTick = System.currentTimeMillis()
+    val snapshots = Kamon(Metrics).collect
+
+    dispatchSelectedMetrics(lastTick, currentTick, subscribedPermanently, snapshots)
+    dispatchSelectedMetrics(lastTick, currentTick, subscribedForOneShot, snapshots)
+
+    lastTick = currentTick
+    subscribedForOneShot = Map.empty
+  }
+
+  def dispatchSelectedMetrics(lastTick: Long, currentTick: Long, subscriptions: Map[MetricGroupFilter, List[ActorRef]],
+    snapshots: Map[MetricGroupIdentity, MetricGroupSnapshot]): Unit = {
+
+    for ((filter, receivers) ← subscriptions) yield {
+      val selection = snapshots.filter(group ⇒ filter.accept(group._1))
+      val tickMetrics = TickMetricSnapshot(lastTick, currentTick, selection)
+
+      receivers.foreach(_ ! tickMetrics)
+    }
+  }
+}
+
+object Subscriptions {
+  case object FlushMetrics
+  case class Subscribe(category: MetricGroupCategory, selection: String, permanently: Boolean = false)
+  case class TickMetricSnapshot(from: Long, to: Long, metrics: Map[MetricGroupIdentity, MetricGroupSnapshot])
+
+  case class MetricGroupFilter(category: MetricGroupCategory, globFilter: GlobPathFilter) {
+    def accept(identity: MetricGroupIdentity): Boolean = {
+      category.equals(identity.category) && globFilter.accept(identity.name)
+    }
+  }
+}
+
+class TickMetricSnapshotBuffer(flushInterval: FiniteDuration, receiver: ActorRef) extends Actor {
+  val flushSchedule = context.system.scheduler.schedule(flushInterval, flushInterval, self, FlushBuffer)(context.dispatcher)
+  val collectionContext = CollectionContext.default
+
+  def receive = empty
+
+  def empty: Actor.Receive = {
+    case tick: TickMetricSnapshot ⇒ context become (buffering(tick))
+    case FlushBuffer              ⇒ // Nothing to flush.
+  }
+
+  def buffering(buffered: TickMetricSnapshot): Actor.Receive = {
+    case TickMetricSnapshot(_, to, tickMetrics) ⇒
+      val combinedMetrics = combineMaps(buffered.metrics, tickMetrics)(mergeMetricGroup)
+      val combinedSnapshot = TickMetricSnapshot(buffered.from, to, combinedMetrics)
+
+      context become (buffering(combinedSnapshot))
+
+    case FlushBuffer ⇒
+      receiver ! buffered
+      context become (empty)
+
+  }
+
+  override def postStop(): Unit = {
+    flushSchedule.cancel()
+    super.postStop()
+  }
+
+  def mergeMetricGroup(left: MetricGroupSnapshot, right: MetricGroupSnapshot) = left.merge(right.asInstanceOf[left.GroupSnapshotType], collectionContext).asInstanceOf[MetricGroupSnapshot] // ??? //Combined(combineMaps(left.metrics, right.metrics)((l, r) ⇒ l.merge(r, collectionContext)))
+}
+
+object TickMetricSnapshotBuffer {
+  case object FlushBuffer
+
+  def props(flushInterval: FiniteDuration, receiver: ActorRef): Props =
+    Props[TickMetricSnapshotBuffer](new TickMetricSnapshotBuffer(flushInterval, receiver))
+}