! 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.

4 files changed, 18 insertions, 29 deletions

diff --git a/kamon-spray/src/main/scala/spray/can/client/ClientRequestInstrumentation.scala b/kamon-spray/src/main/scala/spray/can/client/ClientRequestInstrumentation.scala
index d7d9cf09..d787bda4 100644
--- a/kamon-spray/src/main/scala/spray/can/client/ClientRequestInstrumentation.scala
+++ b/kamon-spray/src/main/scala/spray/can/client/ClientRequestInstrumentation.scala
@@ -21,7 +21,7 @@ import org.aspectj.lang.ProceedingJoinPoint
 import spray.http.{ HttpHeader, HttpResponse, HttpMessageEnd, HttpRequest }
 import spray.http.HttpHeaders.{ RawHeader, Host }
 import kamon.trace.{ TraceRecorder, SegmentCompletionHandleAware }
-import kamon.metrics.TraceMetrics.HttpClientRequest
+import kamon.metric.TraceMetrics.HttpClientRequest
 import kamon.Kamon
 import kamon.spray.{ ClientSegmentCollectionStrategy, Spray }
 import akka.actor.ActorRef
@@ -30,7 +30,6 @@ import akka.util.Timeout
 
 @Aspect
 class ClientRequestInstrumentation {
-  import ClientRequestInstrumentation._
 
   @DeclareMixin("spray.can.client.HttpHostConnector.RequestContext")
   def mixin: SegmentCompletionHandleAware = SegmentCompletionHandleAware.default
@@ -51,7 +50,7 @@ class ClientRequestInstrumentation {
         if (sprayExtension.clientSegmentCollectionStrategy == ClientSegmentCollectionStrategy.Internal) {
           val requestAttributes = basicRequestAttributes(request)
           val clientRequestName = sprayExtension.assignHttpClientRequestName(request)
-          val completionHandle = traceContext.startSegment(HttpClientRequest(clientRequestName, SprayTime), requestAttributes)
+          val completionHandle = traceContext.startSegment(HttpClientRequest(clientRequestName), requestAttributes)
 
           ctx.segmentCompletionHandle = Some(completionHandle)
         }
@@ -102,7 +101,7 @@ class ClientRequestInstrumentation {
         if (sprayExtension.clientSegmentCollectionStrategy == ClientSegmentCollectionStrategy.Pipelining) {
           val requestAttributes = basicRequestAttributes(request)
           val clientRequestName = sprayExtension.assignHttpClientRequestName(request)
-          val completionHandle = traceContext.startSegment(HttpClientRequest(clientRequestName, UserTime), requestAttributes)
+          val completionHandle = traceContext.startSegment(HttpClientRequest(clientRequestName), requestAttributes)
 
           responseFuture.onComplete { result ⇒
             completionHandle.finish(Map.empty)
@@ -139,8 +138,3 @@ class ClientRequestInstrumentation {
     pjp.proceed(Array(modifiedHeaders))
   }
 }
-
-object ClientRequestInstrumentation {
-  val SprayTime = "SprayTime"
-  val UserTime = "UserTime"
-}
diff --git a/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala b/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
index 9469924a..54329645 100644
--- a/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
+++ b/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
@@ -26,13 +26,12 @@ import com.typesafe.config.ConfigFactory
 import spray.can.Http
 import spray.http.HttpHeaders.RawHeader
 import kamon.Kamon
-import kamon.metrics.{ TraceMetrics, Metrics }
+import kamon.metric.{ TraceMetrics, Metrics }
 import spray.client.pipelining
-import kamon.metrics.Subscriptions.TickMetricSnapshot
-import spray.can.client.ClientRequestInstrumentation
+import kamon.metric.Subscriptions.TickMetricSnapshot
 import scala.concurrent.duration._
 import akka.pattern.pipe
-import kamon.metrics.TraceMetrics.TraceMetricSnapshot
+import kamon.metric.TraceMetrics.{ HttpClientRequest, TraceMetricsSnapshot }
 
 class ClientRequestInstrumentationSpec extends TestKitBase with WordSpecLike with Matchers with RequestBuilding with TestServer {
   implicit lazy val system: ActorSystem = ActorSystem("client-request-instrumentation-spec", ConfigFactory.parseString(
@@ -149,7 +148,7 @@ class ClientRequestInstrumentationSpec extends TestKitBase with WordSpecLike wit
         val traceMetrics = expectTraceMetrics("pipelining-strategy-client-request", metricListener, 3 seconds)
         traceMetrics.elapsedTime.numberOfMeasurements should be(1L)
         traceMetrics.segments should not be empty
-        val recordedSegment = traceMetrics.segments.find { case (k, v) ⇒ k.tag == ClientRequestInstrumentation.UserTime } map (_._2)
+        val recordedSegment = traceMetrics.segments.find { case (k, v) ⇒ k.isInstanceOf[HttpClientRequest] } map (_._2)
         recordedSegment should not be empty
         recordedSegment map { segmentMetrics ⇒
           segmentMetrics.numberOfMeasurements should be(1L)
@@ -190,7 +189,7 @@ class ClientRequestInstrumentationSpec extends TestKitBase with WordSpecLike wit
         val traceMetrics = expectTraceMetrics("internal-strategy-client-request", metricListener, 3 seconds)
         traceMetrics.elapsedTime.numberOfMeasurements should be(1L)
         traceMetrics.segments should not be empty
-        val recordedSegment = traceMetrics.segments.find { case (k, v) ⇒ k.tag == ClientRequestInstrumentation.SprayTime } map (_._2)
+        val recordedSegment = traceMetrics.segments.find { case (k, v) ⇒ k.isInstanceOf[HttpClientRequest] } map (_._2)
         recordedSegment should not be empty
         recordedSegment map { segmentMetrics ⇒
           segmentMetrics.numberOfMeasurements should be(1L)
@@ -199,14 +198,14 @@ class ClientRequestInstrumentationSpec extends TestKitBase with WordSpecLike wit
     }
   }
 
-  def expectTraceMetrics(traceName: String, listener: TestProbe, timeout: FiniteDuration): TraceMetricSnapshot = {
+  def expectTraceMetrics(traceName: String, listener: TestProbe, timeout: FiniteDuration): TraceMetricsSnapshot = {
     val tickSnapshot = within(timeout) {
       listener.expectMsgType[TickMetricSnapshot]
     }
 
     val metricsOption = tickSnapshot.metrics.get(TraceMetrics(traceName))
     metricsOption should not be empty
-    metricsOption.get.asInstanceOf[TraceMetricSnapshot]
+    metricsOption.get.asInstanceOf[TraceMetricsSnapshot]
   }
 
   def enableInternalSegmentCollectionStrategy(): Unit = setSegmentCollectionStrategy(ClientSegmentCollectionStrategy.Internal)
diff --git a/kamon-spray/src/test/scala/kamon/spray/ServerRequestInstrumentationSpec.scala b/kamon-spray/src/test/scala/kamon/spray/ServerRequestInstrumentationSpec.scala
index 7edbbe11..ab9116fd 100644
--- a/kamon-spray/src/test/scala/kamon/spray/ServerRequestInstrumentationSpec.scala
+++ b/kamon-spray/src/test/scala/kamon/spray/ServerRequestInstrumentationSpec.scala
@@ -24,10 +24,11 @@ import kamon.Kamon
 import org.scalatest.concurrent.{ PatienceConfiguration, ScalaFutures }
 import spray.http.HttpHeaders.RawHeader
 import spray.http.{ HttpResponse, HttpRequest }
-import kamon.metrics.{ TraceMetrics, Metrics }
-import kamon.metrics.Subscriptions.TickMetricSnapshot
+import kamon.metric.{ TraceMetrics, Metrics }
+import kamon.metric.Subscriptions.TickMetricSnapshot
 import com.typesafe.config.ConfigFactory
-import kamon.metrics.TraceMetrics.ElapsedTime
+import kamon.metric.TraceMetrics.ElapsedTime
+import kamon.metric.instrument.Histogram
 
 class ServerRequestInstrumentationSpec extends TestKitBase with WordSpecLike with Matchers with RequestBuilding
     with ScalaFutures with PatienceConfiguration with TestServer {
@@ -122,7 +123,7 @@ class ServerRequestInstrumentationSpec extends TestKitBase with WordSpecLike wit
       traceMetrics should not be empty
 
       traceMetrics map { metrics ⇒
-        metrics(ElapsedTime).numberOfMeasurements should be(1L)
+        metrics(ElapsedTime).asInstanceOf[Histogram.Snapshot].numberOfMeasurements should be(1L)
       }
     }
 
diff --git a/kamon-spray/src/test/scala/kamon/spray/TestServer.scala b/kamon-spray/src/test/scala/kamon/spray/TestServer.scala
index 81242133..65506770 100644
--- a/kamon-spray/src/test/scala/kamon/spray/TestServer.scala
+++ b/kamon-spray/src/test/scala/kamon/spray/TestServer.scala
@@ -29,11 +29,9 @@ trait TestServer {
   def buildClientConnectionAndServer: (ActorRef, TestProbe) = {
     val serverHandler = TestProbe()
     IO(Http).tell(Http.Bind(listener = serverHandler.ref, interface = "127.0.0.1", port = 0), serverHandler.ref)
-    val bound = within(10 seconds) {
-      serverHandler.expectMsgType[Bound]
-    }
-
+    val bound = serverHandler.expectMsgType[Bound](10 seconds)
     val client = clientConnection(bound)
+
     serverHandler.expectMsgType[Http.Connected]
     serverHandler.reply(Http.Register(serverHandler.ref))
 
@@ -50,10 +48,7 @@ trait TestServer {
   def buildSHostConnectorAndServer: (ActorRef, TestProbe) = {
     val serverHandler = TestProbe()
     IO(Http).tell(Http.Bind(listener = serverHandler.ref, interface = "127.0.0.1", port = 0), serverHandler.ref)
-    val bound = within(10 seconds) {
-      serverHandler.expectMsgType[Bound]
-    }
-
+    val bound = serverHandler.expectMsgType[Bound](10 seconds)
     val client = httpHostConnector(bound)
 
     (client, serverHandler)