HADOOP-11361. Fix a race condition in MetricsSourceAdapter.updateJmxCache. Contributed by Brahma Reddy Battula.

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

@@ -674,6 +674,9 @@ Release 2.8.0 - UNRELEASED
     HADOOP-11962. Sasl message with MD5 challenge text shouldn't be LOG out
     even in debug level. (Junping Du via wheat9)
 
+    HADOOP-11361. Fix a race condition in MetricsSourceAdapter.updateJmxCache.
+    (Brahma Reddy Battula via ozawa)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/MetricsSourceAdapter.java

@@ -154,31 +154,28 @@ class MetricsSourceAdapter implements DynamicMBean {
 
   private void updateJmxCache() {
     boolean getAllMetrics = false;
-    synchronized(this) {
+    synchronized (this) {
       if (Time.now() - jmxCacheTS >= jmxCacheTTL) {
         // temporarilly advance the expiry while updating the cache
         jmxCacheTS = Time.now() + jmxCacheTTL;
         if (lastRecs == null) {
           getAllMetrics = true;
         }
-      }
-      else {
+      } else {
         return;
       }
-    }
 
-    if (getAllMetrics) {
-      MetricsCollectorImpl builder = new MetricsCollectorImpl();
-      getMetrics(builder, true);
-    }
+      if (getAllMetrics) {
+        MetricsCollectorImpl builder = new MetricsCollectorImpl();
+        getMetrics(builder, true);
+      }
 
-    synchronized(this) {
       updateAttrCache();
       if (getAllMetrics) {
         updateInfoCache();
       }
       jmxCacheTS = Time.now();
-      lastRecs = null;  // in case regular interval update is not running
+      lastRecs = null; // in case regular interval update is not running
     }
   }