! 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, 87 insertions, 0 deletions

diff --git a/kamon-core/src/test/scala/kamon/instrumentation/akka/ActorCellInstrumentationSpec.scala b/kamon-core/src/test/scala/kamon/instrumentation/akka/ActorCellInstrumentationSpec.scala
new file mode 100644
index 00000000..0f682500
--- /dev/null
+++ b/kamon-core/src/test/scala/kamon/instrumentation/akka/ActorCellInstrumentationSpec.scala
@@ -0,0 +1,87 @@
+/* ===================================================
+ * 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.instrumentation.akka
+
+import akka.actor.{ Actor, ActorSystem, Props }
+import akka.pattern.{ ask, pipe }
+import akka.routing.RoundRobinPool
+import akka.testkit.{ ImplicitSender, TestKit }
+import akka.util.Timeout
+import kamon.trace.TraceRecorder
+import org.scalatest.WordSpecLike
+
+import scala.concurrent.duration._
+
+class ActorCellInstrumentationSpec extends TestKit(ActorSystem("actor-cell-instrumentation-spec")) with WordSpecLike
+    with ImplicitSender {
+
+  implicit val executionContext = system.dispatcher
+
+  "the message passing instrumentation" should {
+    "propagate the TraceContext using bang" in new EchoActorFixture {
+      val testTraceContext = TraceRecorder.withNewTraceContext("bang-reply") {
+        ctxEchoActor ! "test"
+        TraceRecorder.currentContext
+      }
+
+      expectMsg(testTraceContext)
+    }
+
+    "propagate the TraceContext using tell" in new EchoActorFixture {
+      val testTraceContext = TraceRecorder.withNewTraceContext("tell-reply") {
+        ctxEchoActor.tell("test", testActor)
+        TraceRecorder.currentContext
+      }
+
+      expectMsg(testTraceContext)
+    }
+
+    "propagate the TraceContext using ask" in new EchoActorFixture {
+      implicit val timeout = Timeout(1 seconds)
+      val testTraceContext = TraceRecorder.withNewTraceContext("ask-reply") {
+        // The pipe pattern use Futures internally, so FutureTracing test should cover the underpinnings of it.
+        (ctxEchoActor ? "test") pipeTo (testActor)
+        TraceRecorder.currentContext
+      }
+
+      expectMsg(testTraceContext)
+    }
+
+    "propagate the TraceContext to actors behind a router" in new RoutedEchoActorFixture {
+      val testTraceContext = TraceRecorder.withNewTraceContext("router-reply") {
+        ctxEchoActor ! "test"
+        TraceRecorder.currentContext
+      }
+
+      expectMsg(testTraceContext)
+    }
+  }
+
+  trait EchoActorFixture {
+    val ctxEchoActor = system.actorOf(Props[TraceContextEcho])
+  }
+
+  trait RoutedEchoActorFixture extends EchoActorFixture {
+    override val ctxEchoActor = system.actorOf(Props[TraceContextEcho].withRouter(RoundRobinPool(nrOfInstances = 1)))
+  }
+}
+
+class TraceContextEcho extends Actor {
+  def receive = {
+    case msg: String ⇒ sender ! TraceRecorder.currentContext
+  }
+}
+