! 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, 88 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/DispatcherMetrics.scala b/kamon-core/src/main/scala/kamon/metric/DispatcherMetrics.scala
new file mode 100644
index 00000000..fbce783c
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/DispatcherMetrics.scala
@@ -0,0 +1,88 @@
+/*
+ * =========================================================================================
+ * Copyright © 2013-2014 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 com.typesafe.config.Config
+import kamon.metric.instrument.{ Histogram, HdrHistogram }
+
+case class DispatcherMetrics(name: String) extends MetricGroupIdentity {
+  val category = DispatcherMetrics
+}
+
+object DispatcherMetrics extends MetricGroupCategory {
+  val name = "dispatcher"
+
+  case object MaximumPoolSize extends MetricIdentity { val name = "maximum-pool-size" }
+  case object RunningThreadCount extends MetricIdentity { val name = "running-thread-count" }
+  case object QueueTaskCount extends MetricIdentity { val name = "queued-task-count" }
+  case object PoolSize extends MetricIdentity { val name = "pool-size" }
+
+  case class DispatcherMetricRecorder(maximumPoolSize: Histogram, runningThreadCount: Histogram,
+    queueTaskCount: Histogram, poolSize: Histogram)
+      extends MetricGroupRecorder {
+
+    def collect(context: CollectionContext): MetricGroupSnapshot =
+      DispatcherMetricSnapshot(
+        maximumPoolSize.collect(context),
+        runningThreadCount.collect(context),
+        queueTaskCount.collect(context),
+        poolSize.collect(context))
+
+    def cleanup: Unit = {}
+
+  }
+
+  case class DispatcherMetricSnapshot(maximumPoolSize: Histogram.Snapshot, runningThreadCount: Histogram.Snapshot,
+      queueTaskCount: Histogram.Snapshot, poolSize: Histogram.Snapshot) extends MetricGroupSnapshot {
+
+    type GroupSnapshotType = DispatcherMetricSnapshot
+
+    def merge(that: DispatcherMetricSnapshot, context: CollectionContext): DispatcherMetricSnapshot =
+      DispatcherMetricSnapshot(
+        maximumPoolSize.merge(that.maximumPoolSize, context),
+        runningThreadCount.merge(that.runningThreadCount, context),
+        queueTaskCount.merge(that.queueTaskCount, context),
+        poolSize.merge(that.poolSize, context))
+
+    lazy val metrics: Map[MetricIdentity, MetricSnapshot] = Map(
+      (MaximumPoolSize -> maximumPoolSize),
+      (RunningThreadCount -> runningThreadCount),
+      (QueueTaskCount -> queueTaskCount),
+      (PoolSize -> poolSize))
+  }
+
+  val Factory = new MetricGroupFactory {
+    type GroupRecorder = DispatcherMetricRecorder
+
+    def create(config: Config, system: ActorSystem): DispatcherMetricRecorder = {
+      val settings = config.getConfig("precision.dispatcher")
+
+      val maximumPoolSizeConfig = settings.getConfig("maximum-pool-size")
+      val runningThreadCountConfig = settings.getConfig("running-thread-count")
+      val queueTaskCountConfig = settings.getConfig("queued-task-count")
+      val poolSizeConfig = settings.getConfig("pool-size")
+
+      new DispatcherMetricRecorder(
+        Histogram.fromConfig(maximumPoolSizeConfig),
+        Histogram.fromConfig(runningThreadCountConfig),
+        Histogram.fromConfig(queueTaskCountConfig),
+        Histogram.fromConfig(poolSizeConfig))
+    }
+  }
+}
+