! 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, 109 insertions, 0 deletions

diff --git a/kamon-core/src/test/scala/kamon/metric/TickMetricSnapshotBufferSpec.scala b/kamon-core/src/test/scala/kamon/metric/TickMetricSnapshotBufferSpec.scala
new file mode 100644
index 00000000..ee851672
--- /dev/null
+++ b/kamon-core/src/test/scala/kamon/metric/TickMetricSnapshotBufferSpec.scala
@@ -0,0 +1,109 @@
+/*
+ * =========================================================================================
+ * 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.metric
+
+import com.typesafe.config.ConfigFactory
+import kamon.Kamon
+import kamon.metric.instrument.Histogram
+import kamon.metric.instrument.Histogram.MutableRecord
+import org.scalatest.{ Matchers, WordSpecLike }
+import akka.testkit.{ ImplicitSender, TestKitBase }
+import akka.actor.ActorSystem
+import scala.concurrent.duration._
+import kamon.metric.Subscriptions.TickMetricSnapshot
+
+class TickMetricSnapshotBufferSpec extends TestKitBase with WordSpecLike with Matchers with ImplicitSender {
+  implicit lazy val system: ActorSystem = ActorSystem("trace-metrics-spec", ConfigFactory.parseString(
+    """
+      |kamon.metrics {
+      |  tick-interval = 1 hour
+      |  filters = [
+      |    {
+      |      trace {
+      |        includes = [ "*" ]
+      |        excludes = [ "non-tracked-trace"]
+      |      }
+      |    }
+      |  ]
+      |}
+    """.stripMargin))
+
+  "the TickMetricSnapshotBuffer" should {
+    "merge TickMetricSnapshots received until the flush timeout is reached and fix the from/to fields" in new SnapshotFixtures {
+      val buffer = system.actorOf(TickMetricSnapshotBuffer.props(3 seconds, testActor))
+
+      buffer ! firstEmpty
+      buffer ! secondEmpty
+      buffer ! thirdEmpty
+
+      within(2 seconds)(expectNoMsg())
+      val mergedSnapshot = expectMsgType[TickMetricSnapshot]
+
+      mergedSnapshot.from should equal(1000)
+      mergedSnapshot.to should equal(4000)
+      mergedSnapshot.metrics should be('empty)
+    }
+
+    "merge empty and non-empty snapshots" in new SnapshotFixtures {
+      val buffer = system.actorOf(TickMetricSnapshotBuffer.props(3 seconds, testActor))
+
+      buffer ! firstNonEmpty
+      buffer ! secondNonEmpty
+      buffer ! thirdEmpty
+
+      within(2 seconds)(expectNoMsg())
+      val mergedSnapshot = expectMsgType[TickMetricSnapshot]
+
+      mergedSnapshot.from should equal(1000)
+      mergedSnapshot.to should equal(4000)
+      mergedSnapshot.metrics should not be ('empty)
+
+      val testMetricSnapshot = mergedSnapshot.metrics(testTraceIdentity).metrics(TraceMetrics.ElapsedTime).asInstanceOf[Histogram.Snapshot]
+      testMetricSnapshot.min should equal(10)
+      testMetricSnapshot.max should equal(300)
+      testMetricSnapshot.numberOfMeasurements should equal(6)
+      testMetricSnapshot.recordsIterator.toStream should contain allOf (
+        MutableRecord(10, 3),
+        MutableRecord(20, 1),
+        MutableRecord(30, 1),
+        MutableRecord(300, 1))
+
+    }
+  }
+
+  trait SnapshotFixtures {
+    val collectionContext = CollectionContext.default
+    val testTraceIdentity = TraceMetrics("buffer-spec-test-trace")
+    val traceRecorder = Kamon(Metrics).register(testTraceIdentity, TraceMetrics.Factory).get
+
+    val firstEmpty = TickMetricSnapshot(1000, 2000, Map.empty)
+    val secondEmpty = TickMetricSnapshot(2000, 3000, Map.empty)
+    val thirdEmpty = TickMetricSnapshot(3000, 4000, Map.empty)
+
+    traceRecorder.elapsedTime.record(10L)
+    traceRecorder.elapsedTime.record(20L)
+    traceRecorder.elapsedTime.record(30L)
+    val firstNonEmpty = TickMetricSnapshot(1000, 2000, Map(
+      (testTraceIdentity -> traceRecorder.collect(collectionContext))))
+
+    traceRecorder.elapsedTime.record(10L)
+    traceRecorder.elapsedTime.record(10L)
+    traceRecorder.elapsedTime.record(300L)
+    val secondNonEmpty = TickMetricSnapshot(1000, 2000, Map(
+      (testTraceIdentity -> traceRecorder.collect(collectionContext))))
+  }
+}