! 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, 18 insertions, 14 deletions

diff --git a/kamon-newrelic/src/main/scala/kamon/newrelic/package.scala b/kamon-newrelic/src/main/scala/kamon/newrelic/package.scala
index f6e377c7..89a8b15b 100644
--- a/kamon-newrelic/src/main/scala/kamon/newrelic/package.scala
+++ b/kamon-newrelic/src/main/scala/kamon/newrelic/package.scala
@@ -16,26 +16,30 @@
 
 package kamon
 
-import kamon.metrics.{ Scale, MetricSnapshotLike }
+import kamon.metric.instrument.{ Counter, Histogram }
+import kamon.metric.{ MetricSnapshot, Scale }
 
 package object newrelic {
 
-  def toNewRelicMetric(scale: Scale)(name: String, scope: Option[String], snapshot: MetricSnapshotLike): NewRelic.Metric = {
-    var total: Double = 0D
-    var sumOfSquares: Double = 0D
+  def toNewRelicMetric(scale: Scale)(name: String, scope: Option[String], snapshot: MetricSnapshot): NewRelic.Metric = {
+    snapshot match {
+      case hs: Histogram.Snapshot ⇒
+        var total: Double = 0D
+        var sumOfSquares: Double = 0D
+        val scaledMin = Scale.convert(hs.scale, scale, hs.min)
+        val scaledMax = Scale.convert(hs.scale, scale, hs.max)
 
-    val measurementLevels = snapshot.measurements.iterator
-    while (measurementLevels.hasNext) {
-      val level = measurementLevels.next()
-      val scaledValue = Scale.convert(snapshot.scale, scale, level.value)
+        hs.recordsIterator.foreach { record ⇒
+          val scaledValue = Scale.convert(hs.scale, scale, record.level)
 
-      total += scaledValue * level.count
-      sumOfSquares += (scaledValue * scaledValue) * level.count
-    }
+          total += scaledValue * record.count
+          sumOfSquares += (scaledValue * scaledValue) * record.count
+        }
 
-    val scaledMin = Scale.convert(snapshot.scale, scale, snapshot.min)
-    val scaledMax = Scale.convert(snapshot.scale, scale, snapshot.max)
+        NewRelic.Metric(name, scope, hs.numberOfMeasurements, total, total, scaledMin, scaledMax, sumOfSquares)
 
-    NewRelic.Metric(name, scope, snapshot.numberOfMeasurements, total, total, scaledMin, scaledMax, sumOfSquares)
+      case cs: Counter.Snapshot ⇒
+        NewRelic.Metric(name, scope, cs.count, cs.count, cs.count, 0, cs.count, cs.count * cs.count)
+    }
   }
 }