YARN-10260. Allow transitioning queue from DRAINING to RUNNING state. Contributed by Bilwa S T

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

@@ -1359,10 +1359,6 @@ public abstract class AbstractCSQueue implements CSQueue {
       if (getState() == QueueState.RUNNING) {
         LOG.info("The specified queue:" + getQueuePath()
             + " is already in the RUNNING state.");
-      } else if (getState() == QueueState.DRAINING) {
-        throw new YarnException(
-            "The queue:" + getQueuePath() + " is in the Stopping process. "
-            + "Please wait for the queue getting fully STOPPED.");
       } else {
         CSQueue parent = getParent();
         if (parent == null || parent.getState() == QueueState.RUNNING) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/TestQueueState.java

@@ -157,6 +157,23 @@ public class TestQueueState {
     Assert.assertEquals(QueueState.DRAINING, cs.getQueue(Q2).getState());
     Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q3).getState());
 
+    // set Q2 state to RUNNING and do reinitialize.
+    // Q2 should transit from DRAINING to RUNNING
+    csConf.setState(Q2_PATH, QueueState.RUNNING);
+    conf = new YarnConfiguration(csConf);
+    cs.reinitialize(conf, rmContext);
+    Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q1).getState());
+    Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q2).getState());
+    Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q3).getState());
+
+    // set Q2 state to stop and do reinitialize.
+    csConf.setState(Q2_PATH, QueueState.STOPPED);
+    conf = new YarnConfiguration(csConf);
+    cs.reinitialize(conf, rmContext);
+    Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q1).getState());
+    Assert.assertEquals(QueueState.DRAINING, cs.getQueue(Q2).getState());
+    Assert.assertEquals(QueueState.RUNNING, cs.getQueue(Q3).getState());
+
     // set Q1 state to stop and do reinitialize.
     csConf.setState(Q1_PATH, QueueState.STOPPED);
     conf = new YarnConfiguration(csConf);