! 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, 75 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/metric/EntityMetrics.scala b/kamon-core/src/main/scala/kamon/metric/EntityMetrics.scala
new file mode 100644
index 00000000..325dd216
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/EntityMetrics.scala
@@ -0,0 +1,75 @@
+/*
+ * =========================================================================================
+ * 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 java.nio.{ LongBuffer }
+import akka.actor.ActorSystem
+import com.typesafe.config.Config
+
+trait MetricGroupCategory {
+  def name: String
+}
+
+trait MetricGroupIdentity {
+  def name: String
+  def category: MetricGroupCategory
+}
+
+trait MetricIdentity {
+  def name: String
+}
+
+trait CollectionContext {
+  def buffer: LongBuffer
+}
+
+object CollectionContext {
+  def default: CollectionContext = new CollectionContext {
+    val buffer: LongBuffer = LongBuffer.allocate(10000)
+  }
+}
+
+trait MetricGroupRecorder {
+  def collect(context: CollectionContext): MetricGroupSnapshot
+  def cleanup: Unit
+}
+
+trait MetricSnapshot {
+  type SnapshotType
+
+  def merge(that: SnapshotType, context: CollectionContext): SnapshotType
+}
+
+trait MetricGroupSnapshot {
+  type GroupSnapshotType
+
+  def metrics: Map[MetricIdentity, MetricSnapshot]
+  def merge(that: GroupSnapshotType, context: CollectionContext): GroupSnapshotType
+}
+
+private[kamon] trait MetricRecorder {
+  type SnapshotType <: MetricSnapshot
+
+  def collect(context: CollectionContext): SnapshotType
+  def cleanup: Unit
+}
+
+trait MetricGroupFactory {
+  type GroupRecorder <: MetricGroupRecorder
+  def create(config: Config, system: ActorSystem): GroupRecorder
+}
+