! 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, 89 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/ActorMetrics.scala b/kamon-core/src/main/scala/kamon/metric/ActorMetrics.scala
new file mode 100644
index 00000000..bb412f79
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/ActorMetrics.scala
@@ -0,0 +1,89 @@
+/*
+ * =========================================================================================
+ * 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.{ MinMaxCounter, Counter, Histogram }
+
+case class ActorMetrics(name: String) extends MetricGroupIdentity {
+  val category = ActorMetrics
+}
+
+object ActorMetrics extends MetricGroupCategory {
+  val name = "actor"
+
+  case object ProcessingTime extends MetricIdentity { val name = "processing-time" }
+  case object MailboxSize extends MetricIdentity { val name = "mailbox-size" }
+  case object TimeInMailbox extends MetricIdentity { val name = "time-in-mailbox" }
+  case object Errors extends MetricIdentity { val name = "errors" }
+
+  case class ActorMetricsRecorder(processingTime: Histogram, timeInMailbox: Histogram, mailboxSize: MinMaxCounter,
+      errors: Counter) extends MetricGroupRecorder {
+
+    def collect(context: CollectionContext): ActorMetricSnapshot =
+      ActorMetricSnapshot(
+        processingTime.collect(context),
+        timeInMailbox.collect(context),
+        mailboxSize.collect(context),
+        errors.collect(context))
+
+    def cleanup: Unit = {
+      processingTime.cleanup
+      mailboxSize.cleanup
+      timeInMailbox.cleanup
+      errors.cleanup
+    }
+  }
+
+  case class ActorMetricSnapshot(processingTime: Histogram.Snapshot, timeInMailbox: Histogram.Snapshot,
+      mailboxSize: Histogram.Snapshot, errors: Counter.Snapshot) extends MetricGroupSnapshot {
+
+    type GroupSnapshotType = ActorMetricSnapshot
+
+    def merge(that: ActorMetricSnapshot, context: CollectionContext): ActorMetricSnapshot =
+      ActorMetricSnapshot(
+        processingTime.merge(that.processingTime, context),
+        timeInMailbox.merge(that.timeInMailbox, context),
+        mailboxSize.merge(that.mailboxSize, context),
+        errors.merge(that.errors, context))
+
+    lazy val metrics: Map[MetricIdentity, MetricSnapshot] = Map(
+      (ProcessingTime -> processingTime),
+      (MailboxSize -> mailboxSize),
+      (TimeInMailbox -> timeInMailbox),
+      (Errors -> errors))
+  }
+
+  val Factory = new MetricGroupFactory {
+    type GroupRecorder = ActorMetricsRecorder
+
+    def create(config: Config, system: ActorSystem): ActorMetricsRecorder = {
+      val settings = config.getConfig("precision.actor")
+
+      val processingTimeConfig = settings.getConfig("processing-time")
+      val timeInMailboxConfig = settings.getConfig("time-in-mailbox")
+      val mailboxSizeConfig = settings.getConfig("mailbox-size")
+
+      new ActorMetricsRecorder(
+        Histogram.fromConfig(processingTimeConfig),
+        Histogram.fromConfig(timeInMailboxConfig),
+        MinMaxCounter.fromConfig(mailboxSizeConfig, system),
+        Counter())
+    }
+  }
+}