From 9534d698ccf7e7c368db5e896abdb5d13ce27a48 Mon Sep 17 00:00:00 2001
From: Ivan Topolnak <itopolnak@despegar.com>
Date: Mon, 3 Feb 2014 15:10:40 -0300
Subject: continuous hdr tracking instrument, special for mailbox size metrics

---
 .../main/scala/kamon/metrics/ActorMetrics.scala    |  3 +-
 .../ContinuousHighDynamicRangeRecorder.scala       | 50 ++++++++++++++++++++++
 .../spray/ClientRequestInstrumentationSpec.scala   |  2 -
 3 files changed, 52 insertions(+), 3 deletions(-)
 create mode 100644 kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHighDynamicRangeRecorder.scala

diff --git a/kamon-core/src/main/scala/kamon/metrics/ActorMetrics.scala b/kamon-core/src/main/scala/kamon/metrics/ActorMetrics.scala
index 66d3f888..a00b443e 100644
--- a/kamon-core/src/main/scala/kamon/metrics/ActorMetrics.scala
+++ b/kamon-core/src/main/scala/kamon/metrics/ActorMetrics.scala
@@ -17,6 +17,7 @@
 package kamon.metrics
 
 import com.typesafe.config.Config
+import kamon.metrics.instruments.ContinuousHighDynamicRangeRecorder
 import org.HdrHistogram.HighDynamicRangeRecorder
 
 object ActorMetrics extends MetricGroupIdentity.Category with MetricGroupFactory {
@@ -60,7 +61,7 @@ object ActorMetrics extends MetricGroupIdentity.Category with MetricGroupFactory
 
     new ActorMetricRecorder(
       HighDynamicRangeRecorder(processingTimeHdrConfig),
-      HighDynamicRangeRecorder(mailboxSizeHdrConfig),
+      ContinuousHighDynamicRangeRecorder(mailboxSizeHdrConfig),
       HighDynamicRangeRecorder(timeInMailboxHdrConfig))
   }
 }
diff --git a/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHighDynamicRangeRecorder.scala b/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHighDynamicRangeRecorder.scala
new file mode 100644
index 00000000..533e06b1
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHighDynamicRangeRecorder.scala
@@ -0,0 +1,50 @@
+/*
+ * =========================================================================================
+ * 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.metrics.instruments
+
+import org.HdrHistogram.HighDynamicRangeRecorder
+import org.HdrHistogram.HighDynamicRangeRecorder.Configuration
+import kamon.metrics.MetricSnapshot
+
+/**
+ *  This recorder keeps track of the last value recoded and automatically adds it after collecting a snapshot. This is
+ *  useful in cases where the absence of recordings does not necessarily mean the absence of values. For example, if this
+ *  recorder is used for recording the mailbox size of an actor, and it only gets updated upon message enqueue o dequeue,
+ *  the absence of recordings during 1 second means that the size hasn't change (example: the actor being blocked doing
+ *  some work) and it should keep its last known value, instead of dropping to zero and then going back to the real value
+ *  after a new event is processed.
+ *
+ */
+class ContinuousHighDynamicRangeRecorder(configuration: Configuration) extends HighDynamicRangeRecorder(configuration) {
+  @volatile private var lastRecordedValue: Long = 0
+
+  override def record(value: Long): Unit = {
+    lastRecordedValue = value
+    super.record(value)
+  }
+
+  override def collect(): MetricSnapshot = {
+    val snapshot = super.collect()
+    super.record(lastRecordedValue)
+
+    snapshot
+  }
+}
+
+object ContinuousHighDynamicRangeRecorder {
+  def apply(configuration: Configuration) = new ContinuousHighDynamicRangeRecorder(configuration)
+}
\ No newline at end of file
diff --git a/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala b/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
index 8163e25c..0b1db1b7 100644
--- a/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
+++ b/kamon-spray/src/test/scala/kamon/spray/ClientRequestInstrumentationSpec.scala
@@ -74,13 +74,11 @@ class ClientRequestInstrumentationSpec extends TestKitBase with WordSpecLike wit
       }
     }
 
-
     "record the elapsed time for a http request when using the pipelining sendReceive and tag it as UserTime" in {
 
       val metricListener = TestProbe()
       Kamon(Metrics)(system).subscribe(TraceMetrics, "*", metricListener.ref, permanently = true)
 
-
       val (hostConnector, server) = buildSHostConnectorAndServer
       val client = TestProbe()
       val pipeline = pipelining.sendReceive(hostConnector)(system.dispatcher, 10 seconds)
-- 
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