YARN-7052. RM SchedulingMonitor gives no indication why the spawned thread crashed. Contributed by Eric Payne

(cherry picked from commit 39a9dc8e4a6e1d13658867ad756878d3dd6352b0)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/SchedulingMonitor.java

@@ -102,9 +102,11 @@ public class SchedulingMonitor extends AbstractService {
       try {
         //invoke the preemption policy
         invokePolicy();
-      } catch (YarnRuntimeException e) {
-        LOG.error("YarnRuntimeException raised while executing preemption"
-            + " checker, skip this run..., exception=", e);
+      } catch (Throwable t) {
+        // The preemption monitor does not alter structures nor do structures
+        // persist across invocations. Therefore, log, skip, and retry.
+        LOG.error("Exception raised while executing preemption"
+            + " checker, skip this run..., exception=", t);
       }
     }
   }