! 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, 35 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/instrumentation/hdrhistogram/AtomicHistogramFieldsAccessor.scala b/kamon-core/src/main/scala/kamon/instrumentation/hdrhistogram/AtomicHistogramFieldsAccessor.scala
new file mode 100644
index 00000000..e79090a8
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/instrumentation/hdrhistogram/AtomicHistogramFieldsAccessor.scala
@@ -0,0 +1,35 @@
+/*
+ * =========================================================================================
+ * Copyright © 2013-2014 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 org.HdrHistogram
+
+import java.util.concurrent.atomic.{ AtomicLongArray, AtomicLongFieldUpdater }
+
+trait AtomicHistogramFieldsAccessor {
+  self: AtomicHistogram ⇒
+
+  def countsArray(): AtomicLongArray = self.counts
+
+  def unitMagnitude(): Int = self.unitMagnitude
+
+  def subBucketHalfCount(): Int = self.subBucketHalfCount
+
+  def subBucketHalfCountMagnitude(): Int = self.subBucketHalfCountMagnitude
+}
+
+object AtomicHistogramFieldsAccessor {
+  def totalCountUpdater(): AtomicLongFieldUpdater[AtomicHistogram] = AtomicHistogram.totalCountUpdater
+}