IntentPerfCollector Synch issue fix

Change-Id: I7bd56459476dd87e6c29127b4e17366c23416768
diff --git a/apps/test/intent-perf/src/main/java/org/onosproject/intentperf/IntentPerfCollector.java b/apps/test/intent-perf/src/main/java/org/onosproject/intentperf/IntentPerfCollector.java
index 8c160e8..cae5455 100644
--- a/apps/test/intent-perf/src/main/java/org/onosproject/intentperf/IntentPerfCollector.java
+++ b/apps/test/intent-perf/src/main/java/org/onosproject/intentperf/IntentPerfCollector.java
@@ -106,7 +106,7 @@
     /**
      * Clears all previously accumulated data.
      */
-    public void clearSamples() {
+    public synchronized void clearSamples() {
         newestTime = 0;
         overall = new Sample(0, nodes.length);
         current = new Sample(0, nodes.length);