From cd1e2519140211253120d49c8457e34833c6a3e9 Mon Sep 17 00:00:00 2001
From: Ivan Topolnjak <ivantopo@gmail.com>
Date: Wed, 13 Aug 2014 00:13:21 -0400
Subject: = core: ensure that MinMaxCounters never record values bellow zero,
 fixes #71

---
 .../src/main/java/kamon/jsr166/LongMaxUpdater.java |  6 ++--
 .../kamon/metric/instrument/MinMaxCounter.scala    | 17 +++++----
 .../metric/instrument/MinMaxCounterSpec.scala      | 40 ++++++++++++++++++++--
 3 files changed, 50 insertions(+), 13 deletions(-)

diff --git a/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java b/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java
index e4ba8807..fc9ea4e5 100644
--- a/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java
+++ b/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java
@@ -114,17 +114,17 @@ public class LongMaxUpdater extends Striped64 implements Serializable {
      *
      * @return the maximum
      */
-    public long maxThenReset() {
+    public long maxThenReset(long newValue) {
         Cell[] as = cells;
         long max = base;
-        base = Long.MIN_VALUE;
+        base = newValue;
         if (as != null) {
             int n = as.length;
             for (int i = 0; i < n; ++i) {
                 Cell a = as[i];
                 if (a != null) {
                     long v = a.value;
-                    a.value = Long.MIN_VALUE;
+                    a.value = newValue;
                     if (v > max)
                         max = v;
                 }
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala b/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
index 13dea8fe..4882d2aa 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
@@ -33,6 +33,7 @@ trait MinMaxCounter extends MetricRecorder {
   def increment(times: Long): Unit
   def decrement()
   def decrement(times: Long)
+  def refreshValues(): Unit
 }
 
 object MinMaxCounter {
@@ -95,19 +96,21 @@ class PaddedMinMaxCounter(underlyingHistogram: Histogram) extends MinMaxCounter
   def refreshValues(): Unit = {
     val currentValue = {
       val value = sum.get()
-      if (value < 0) 0 else value
+      if (value <= 0) 0 else value
     }
 
     val currentMin = {
-      val minAbs = abs(min.maxThenReset())
-      if (minAbs <= currentValue) minAbs else 0
+      val rawMin = min.maxThenReset(-currentValue)
+      if (rawMin >= 0)
+        0
+      else
+        abs(rawMin)
     }
 
+    val currentMax = max.maxThenReset(currentValue)
+
     underlyingHistogram.record(currentValue)
     underlyingHistogram.record(currentMin)
-    underlyingHistogram.record(max.maxThenReset())
-
-    max.update(currentValue)
-    min.update(-currentValue)
+    underlyingHistogram.record(currentMax)
   }
 }
diff --git a/kamon-core/src/test/scala/kamon/metric/instrument/MinMaxCounterSpec.scala b/kamon-core/src/test/scala/kamon/metric/instrument/MinMaxCounterSpec.scala
index cb03664c..2c11adc3 100644
--- a/kamon-core/src/test/scala/kamon/metric/instrument/MinMaxCounterSpec.scala
+++ b/kamon-core/src/test/scala/kamon/metric/instrument/MinMaxCounterSpec.scala
@@ -17,14 +17,15 @@ package kamon.metric.instrument
 
 import java.nio.LongBuffer
 
-import akka.actor.ActorSystem
+import akka.actor._
+import akka.testkit.TestProbe
 import com.typesafe.config.ConfigFactory
 import kamon.metric.CollectionContext
 import kamon.metric.instrument.Histogram.MutableRecord
 import org.scalatest.{ Matchers, WordSpecLike }
 
 class MinMaxCounterSpec extends WordSpecLike with Matchers {
-  val system = ActorSystem("min-max-counter-spec")
+  implicit val system = ActorSystem("min-max-counter-spec")
   val minMaxCounterConfig = ConfigFactory.parseString(
     """
       |refresh-interval = 1 hour
@@ -83,7 +84,7 @@ class MinMaxCounterSpec extends WordSpecLike with Matchers {
         MutableRecord(2, 3)) // min, max and current
     }
 
-    "report zero as the min and current values if they current value fell bellow zero" in new MinMaxCounterFixture {
+    "report zero as the min and current values if the current value fell bellow zero" in new MinMaxCounterFixture {
       mmCounter.decrement(3)
 
       val snapshot = collectCounterSnapshot()
@@ -93,6 +94,22 @@ class MinMaxCounterSpec extends WordSpecLike with Matchers {
       snapshot.recordsIterator.toStream should contain(
         MutableRecord(0, 3)) // min, max and current (even while current really is -3
     }
+
+    "never record values bellow zero in very busy situations" in new MinMaxCounterFixture {
+      val monitor = TestProbe()
+      val workers = for (workers ← 1 to 50) yield {
+        system.actorOf(Props(new MinMaxCounterUpdateActor(mmCounter, monitor.ref)))
+      }
+
+      workers foreach (_ ! "increment")
+      for (refresh ← 1 to 1000) {
+        collectCounterSnapshot()
+        Thread.sleep(10)
+      }
+
+      monitor.expectNoMsg()
+      workers foreach (_ ! PoisonPill)
+    }
   }
 
   trait MinMaxCounterFixture {
@@ -106,3 +123,20 @@ class MinMaxCounterSpec extends WordSpecLike with Matchers {
     def collectCounterSnapshot(): Histogram.Snapshot = mmCounter.collect(collectionContext)
   }
 }
+
+class MinMaxCounterUpdateActor(mmc: MinMaxCounter, monitor: ActorRef) extends Actor {
+  val x = Array.ofDim[Int](4)
+  def receive = {
+    case "increment" ⇒
+      mmc.increment()
+      self ! "decrement"
+    case "decrement" ⇒
+      mmc.decrement()
+      self ! "increment"
+      try {
+        mmc.refreshValues()
+      } catch {
+        case _: IndexOutOfBoundsException ⇒ monitor ! "failed"
+      }
+  }
+}
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