HADOOP-3957. Change MutableQuantiles to use a shared thread for rolling over metrics. Contributed by Andrew Wang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1390210 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -244,6 +244,9 @@ Trunk (Unreleased)
     required context item is not configured
     (Brahma Reddy Battula via harsh)
 
+    HADOOP-3957. Change MutableQuantiles to use a shared thread for rolling
+    over metrics. (Andrew Wang via todd)
+
   OPTIMIZATIONS
 
     HADOOP-7761. Improve the performance of raw comparisons. (todd)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/lib/MutableQuantiles.java

@@ -35,6 +35,7 @@ import org.apache.hadoop.metrics2.util.Quantile;
 import org.apache.hadoop.metrics2.util.SampleQuantiles;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
 
 /**
  * Watches a stream of long values, maintaining online estimates of specific
@@ -60,8 +61,9 @@ public class MutableQuantiles extends MutableMetric {
   @VisibleForTesting
   protected Map<Quantile, Long> previousSnapshot = null;
 
-  private final ScheduledExecutorService scheduler = Executors
-      .newScheduledThreadPool(1);
+  private static final ScheduledExecutorService scheduler = Executors
+      .newScheduledThreadPool(1, new ThreadFactoryBuilder().setDaemon(true)
+          .setNameFormat("MutableQuantiles-%d").build());
 
   /**
    * Instantiates a new {@link MutableQuantiles} for a metric that rolls itself