! 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, 77 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/TraceMetrics.scala b/kamon-core/src/main/scala/kamon/metric/TraceMetrics.scala
new file mode 100644
index 00000000..1ee1eab4
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/TraceMetrics.scala
@@ -0,0 +1,77 @@
+/*
+ * =========================================================================================
+ * 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.ActorSystem
+import kamon.metric.instrument.{ Histogram }
+
+import scala.collection.concurrent.TrieMap
+import com.typesafe.config.Config
+
+case class TraceMetrics(name: String) extends MetricGroupIdentity {
+  val category = TraceMetrics
+}
+
+object TraceMetrics extends MetricGroupCategory {
+  val name = "trace"
+
+  case object ElapsedTime extends MetricIdentity { val name = "elapsed-time" }
+  case class HttpClientRequest(name: String) extends MetricIdentity
+
+  case class TraceMetricRecorder(elapsedTime: Histogram, private val segmentRecorderFactory: () ⇒ Histogram)
+      extends MetricGroupRecorder {
+
+    private val segments = TrieMap[MetricIdentity, Histogram]()
+
+    def segmentRecorder(segmentIdentity: MetricIdentity): Histogram =
+      segments.getOrElseUpdate(segmentIdentity, segmentRecorderFactory.apply())
+
+    def collect(context: CollectionContext): TraceMetricsSnapshot =
+      TraceMetricsSnapshot(
+        elapsedTime.collect(context),
+        segments.map { case (identity, recorder) ⇒ (identity, recorder.collect(context)) }.toMap)
+
+    def cleanup: Unit = {}
+  }
+
+  case class TraceMetricsSnapshot(elapsedTime: Histogram.Snapshot, segments: Map[MetricIdentity, Histogram.Snapshot])
+      extends MetricGroupSnapshot {
+
+    type GroupSnapshotType = TraceMetricsSnapshot
+
+    def merge(that: TraceMetricsSnapshot, context: CollectionContext): TraceMetricsSnapshot =
+      TraceMetricsSnapshot(elapsedTime.merge(that.elapsedTime, context), Map.empty)
+
+    def metrics: Map[MetricIdentity, MetricSnapshot] = segments + (ElapsedTime -> elapsedTime)
+  }
+
+  val Factory = new MetricGroupFactory {
+    type GroupRecorder = TraceMetricRecorder
+
+    def create(config: Config, system: ActorSystem): TraceMetricRecorder = {
+
+      val settings = config.getConfig("precision.trace")
+      val elapsedTimeConfig = settings.getConfig("elapsed-time")
+      val segmentConfig = settings.getConfig("segment")
+
+      new TraceMetricRecorder(
+        Histogram.fromConfig(elapsedTimeConfig),
+        () ⇒ Histogram.fromConfig(segmentConfig))
+    }
+  }
+
+}