From af11bfdbf7b452b28bd64ed560432dc0d02c85dd Mon Sep 17 00:00:00 2001
From: Ivan Topolnak <itopolnak@despegar.com>
Date: Wed, 9 Apr 2014 16:13:29 -0300
Subject: = core: workaround border cases where mailbox size counting might
 fall bellow zero

---
 .../scala/akka/instrumentation/ActorMessagePassingTracing.scala  | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kamon-core/src/main/scala/akka/instrumentation/ActorMessagePassingTracing.scala b/kamon-core/src/main/scala/akka/instrumentation/ActorMessagePassingTracing.scala
index 85a47ee3..87ad4f92 100644
--- a/kamon-core/src/main/scala/akka/instrumentation/ActorMessagePassingTracing.scala
+++ b/kamon-core/src/main/scala/akka/instrumentation/ActorMessagePassingTracing.scala
@@ -59,7 +59,10 @@ class BehaviourInvokeTracing {
         am ⇒
           am.processingTime.record(System.nanoTime() - timestampBeforeProcessing)
           am.timeInMailbox.record(timestampBeforeProcessing - contextAndTimestamp.captureNanoTime)
-          am.mailboxSize.record(cellWithMetrics.queueSize.decrementAndGet())
+
+          val currentMailboxSize = cellWithMetrics.queueSize.decrementAndGet()
+          if(currentMailboxSize >= 0)
+            am.mailboxSize.record(currentMailboxSize)
       }
     }
   }
@@ -72,7 +75,9 @@ class BehaviourInvokeTracing {
     val cellWithMetrics = cell.asInstanceOf[ActorCellMetrics]
     cellWithMetrics.actorMetricsRecorder.map {
       am ⇒
-        am.mailboxSize.record(cellWithMetrics.queueSize.incrementAndGet())
+        val currentMailboxSize = cellWithMetrics.queueSize.incrementAndGet()
+        if(currentMailboxSize >= 0)
+          am.mailboxSize.record(currentMailboxSize)
     }
   }
 
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