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

(cherry picked from commit 4356e8a5ef)

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

@@ -212,6 +212,9 @@ 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

@@ -154,25 +154,22 @@ 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);
       }
 
-    synchronized(this) {
       updateAttrCache();
       if (getAllMetrics) {
         updateInfoCache();