Rebased ScopeImpl to use CopyOnWriteArrayList instead of `Concurr…

…entLinkedQueue`, to avoid read path peanlty of the CLQ, since reporting list is "write once, read many" use-case

core/src/main/java/com/uber/m3/tally/ScopeImpl.java

@@ -29,7 +29,7 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.ScheduledExecutorService;
 
 /**
@@ -49,7 +49,7 @@ class ScopeImpl implements Scope {
     private final ConcurrentHashMap<String, GaugeImpl> gauges = new ConcurrentHashMap<>();
     private final ConcurrentHashMap<String, HistogramImpl> histograms = new ConcurrentHashMap<>();
 
-    private final ConcurrentLinkedQueue<Reportable> reportingQueue = new ConcurrentLinkedQueue<>();
+    private final CopyOnWriteArrayList<Reportable> reportingList = new CopyOnWriteArrayList<>();
 
     private final ConcurrentHashMap<String, TimerImpl> timers = new ConcurrentHashMap<>();
 
@@ -137,15 +137,15 @@ public void close() {
     }
 
     <T extends Reportable> void addToReportingQueue(T metric) {
-        reportingQueue.add(metric);
+        reportingList.add(metric);
     }
 
     /**
      * Reports using the specified reporter.
      * @param reporter the reporter to report
      */
     void report(StatsReporter reporter) {
-        for (Reportable metric : reportingQueue) {
+        for (Reportable metric : reportingList) {
             metric.report(tags, reporter);
         }
     }