YARN-6376. Exceptions caused by synchronous putEntities requests can be swallowed (Haibo Chen via Varun Saxena)

(cherry picked from commit b58777a9c9a5b6f2e4bcfd2b3bede33f25f80dec)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-timelineservice/src/main/java/org/apache/hadoop/yarn/server/timelineservice/collector/TimelineCollector.java

@@ -137,8 +137,14 @@ public TimelineWriteResponse putEntities(TimelineEntities entities,
           + callerUgi + ")");
     }
 
-    TimelineWriteResponse response = writeTimelineEntities(entities);
-    flushBufferedTimelineEntities();
+    TimelineWriteResponse response;
+    // synchronize on the writer object so that no other threads can
+    // flush the writer buffer concurrently and swallow any exception
+    // caused by the timeline enitites that are being put here.
+    synchronized (writer) {
+      response = writeTimelineEntities(entities);
+      flushBufferedTimelineEntities();
+    }
 
     return response;
   }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-timelineservice/src/main/java/org/apache/hadoop/yarn/server/timelineservice/collector/TimelineCollectorManager.java

@@ -259,7 +259,12 @@ public WriterFlushTask(TimelineWriter writer) {
 
     public void run() {
       try {
-        writer.flush();
+        // synchronize on the writer object to avoid flushing timeline
+        // entities placed on the buffer by synchronous putEntities
+        // requests.
+        synchronized (writer) {
+          writer.flush();
+        }
       } catch (Throwable th) {
         // we need to handle all exceptions or subsequent execution may be
         // suppressed