YARN-9552. FairScheduler: NODE_UPDATE can cause NoSuchElementException. Contributed by Peter Bacsko.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/AppSchedulingInfo.java

@@ -499,12 +499,15 @@ public List<SchedulingRequest> getAllSchedulingRequests() {
   public PendingAsk getNextPendingAsk() {
     readLock.lock();
     try {
-      SchedulerRequestKey firstRequestKey = schedulerKeys.first();
+      if (!schedulerKeys.isEmpty()) {
-      return getPendingAsk(firstRequestKey, ResourceRequest.ANY);
+        SchedulerRequestKey firstRequestKey = schedulerKeys.first();
+        return getPendingAsk(firstRequestKey, ResourceRequest.ANY);
+      } else {
+        return null;
+      }
     } finally {
       readLock.unlock();
     }
-
   }
 
   public PendingAsk getPendingAsk(SchedulerRequestKey schedulerKey) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FSAppAttempt.java

@@ -926,8 +926,8 @@ private boolean isOverAMShareLimit() {
     if (!isAmRunning() && !getUnmanagedAM()) {
       // Return true if we have not ask, or queue is not be able to run app's AM
       PendingAsk ask = appSchedulingInfo.getNextPendingAsk();
-      if (ask.getCount() == 0 || !getQueue().canRunAppAM(
+      if (ask != null && (ask.getCount() == 0 || !getQueue().canRunAppAM(
-          ask.getPerAllocationResource())) {
+          ask.getPerAllocationResource()))) {
         return true;
       }
     }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFSAppAttempt.java

@@ -19,7 +19,10 @@
 package org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.yarn.api.records.Resource;
@@ -33,9 +36,13 @@
 import static org.mockito.Mockito.spy;
 
 import org.apache.hadoop.yarn.api.records.ApplicationAttemptId;
+import org.apache.hadoop.yarn.api.records.ApplicationId;
+import org.apache.hadoop.yarn.api.records.ApplicationSubmissionContext;
+import org.apache.hadoop.yarn.api.records.LogAggregationContext;
 import org.apache.hadoop.yarn.api.records.Priority;
 import org.apache.hadoop.yarn.server.resourcemanager.RMContext;
 import org.apache.hadoop.yarn.server.resourcemanager.placement.ApplicationPlacementContext;
+import org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMApp;
 import org.apache.hadoop.yarn.server.resourcemanager.rmnode.RMNode;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.NodeType;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.QueueMetrics;
@@ -344,6 +351,39 @@ public void testHeadroomWithBlackListedNodes() {
     assertEquals(clusterResource, spyApp.getHeadroom());
   }
 
+  /**
+   * Ensure that no pending ask request inside appSchedulingInfo
+   * does not result in an error.
+   */
+  @Test
+  public void testNoNextPendingAsk() {
+    FSLeafQueue queue = Mockito.mock(FSLeafQueue.class);
+    ApplicationAttemptId applicationAttemptId = createAppAttemptId(1, 1);
+    RMContext rmContext = Mockito.mock(RMContext.class);
+    ConcurrentMap<ApplicationId, RMApp> rmApps = new ConcurrentHashMap<>();
+    RMApp rmApp = Mockito.mock(RMApp.class);
+    rmApps.put(applicationAttemptId.getApplicationId(), rmApp);
+    ApplicationSubmissionContext appContext =
+        Mockito.mock(ApplicationSubmissionContext.class);
+    Mockito.when(appContext.getUnmanagedAM()).thenReturn(false);
+    Mockito.when(appContext.getLogAggregationContext())
+        .thenReturn(Mockito.mock(LogAggregationContext.class));
+    Mockito.when(rmApp.getApplicationSchedulingEnvs())
+        .thenReturn(new HashMap<>());
+    Mockito.when(rmApp.getApplicationSubmissionContext())
+      .thenReturn(appContext);
+    Mockito.when(rmContext.getRMApps()).thenReturn(rmApps);
+    FSAppAttempt schedulerApp =
+        new FSAppAttempt(scheduler, applicationAttemptId, "user1", queue,
+            null, rmContext);
+    schedulerApp.setAmRunning(false);
+    FSSchedulerNode schedulerNode = Mockito.mock(FSSchedulerNode.class);
+
+    Resource resource = schedulerApp.assignContainer(schedulerNode);
+
+    assertEquals(Resources.none(), resource);
+  }
+
   private static long min(long value1, long value2, long value3) {
     return Math.min(Math.min(value1, value2), value3);
   }