! all: improve the metric recorders infrastructure

1 files changed, 41 insertions, 0 deletions

diff --git a/kamon-system-metrics/src/main/scala/kamon/system/sigar/DiffRecordingHistogram.scala b/kamon-system-metrics/src/main/scala/kamon/system/sigar/DiffRecordingHistogram.scala
new file mode 100644
index 00000000..94aa76d1
--- /dev/null
+++ b/kamon-system-metrics/src/main/scala/kamon/system/sigar/DiffRecordingHistogram.scala
@@ -0,0 +1,41 @@
+package kamon.system.sigar
+
+import java.util.concurrent.atomic.AtomicLong
+
+import kamon.metric.instrument.{ CollectionContext, Histogram }
+
+/**
+ *  Wrapper Histogram for cases in which the recorded values should always be the difference
+ *  between the current value and the last recorded value. This is not thread-safe and only
+ *  to be used with Sigar-based metrics that are securely updated within an actor.
+ */
+class DiffRecordingHistogram(wrappedHistogram: Histogram) extends Histogram {
+  @volatile private var _recordedAtLeastOnce = false
+  private val _lastObservedValue = new AtomicLong(0)
+
+  private def processRecording(value: Long, count: Long): Unit = {
+    if (_recordedAtLeastOnce)
+      wrappedHistogram.record(value - _lastObservedValue.getAndSet(value), count)
+    else {
+      _lastObservedValue.set(value)
+      _recordedAtLeastOnce = true
+    }
+  }
+
+  def record(value: Long): Unit =
+    processRecording(value, 1)
+
+  def record(value: Long, count: Long): Unit =
+    processRecording(value, count)
+
+  def cleanup: Unit =
+    wrappedHistogram.cleanup
+
+  def collect(context: CollectionContext): Histogram.Snapshot =
+    wrappedHistogram.collect(context)
+}
+
+object DiffRecordingHistogram {
+  def apply(histogram: Histogram): DiffRecordingHistogram =
+    new DiffRecordingHistogram(histogram)
+}
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