1 files changed, 52 insertions, 0 deletions
diff --git a/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHdrRecorder.scala b/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHdrRecorder.scala
new file mode 100644
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+++ b/kamon-core/src/main/scala/kamon/metrics/instruments/ContinuousHdrRecorder.scala
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+/*
+ * =========================================================================================
+ * 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.HdrRecorder
+import kamon.metrics.{ Scale, MetricSnapshotLike }
+
+/**
+ *  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 ContinuousHdrRecorder(highestTrackableValue: Long, significantValueDigits: Int, scale: Scale)
+    extends HdrRecorder(highestTrackableValue, significantValueDigits, scale) {
+
+  @volatile private var lastRecordedValue: Long = 0
+
+  override def record(value: Long): Unit = {
+    lastRecordedValue = value
+    super.record(value)
+  }
+
+  override def collect(): MetricSnapshotLike = {
+    val snapshot = super.collect()
+    super.record(lastRecordedValue)
+
+    snapshot
+  }
+}
+
+object ContinuousHdrRecorder {
+  def apply(highestTrackableValue: Long, significantValueDigits: Int, scale: Scale) =
+    new ContinuousHdrRecorder(highestTrackableValue, significantValueDigits, scale)
+}
+\ No newline at end of file