HBASE-26643 LoadBalancer should not return empty map (#4005)

Signed-off-by: Yulin Niu <niuyulin@apache.org>

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BaseLoadBalancer.java

@@ -292,7 +292,7 @@ public abstract class BaseLoadBalancer implements LoadBalancer {
     int numServers = servers == null ? 0 : servers.size();
     if (numServers == 0) {
       LOG.warn("Wanted to do round robin assignment but no servers to assign to");
-      return Collections.emptyMap();
+      return Collections.singletonMap(BOGUS_SERVER_NAME, new ArrayList<>(regions));
     }
 
     // TODO: instead of retainAssignment() and roundRobinAssignment(), we should just run the
@@ -432,7 +432,7 @@ public abstract class BaseLoadBalancer implements LoadBalancer {
     int numServers = servers == null ? 0 : servers.size();
     if (numServers == 0) {
       LOG.warn("Wanted to do retain assignment but no servers to assign to");
-      return Collections.emptyMap();
+      return Collections.singletonMap(BOGUS_SERVER_NAME, new ArrayList<>(regions.keySet()));
     }
     if (numServers == 1) { // Only one server, nothing fancy we can do here
       ServerName server = servers.get(0);

hbase-server/src/test/java/org/apache/hadoop/hbase/master/procedure/TestCreateTableNoRegionServer.java

@@ -0,0 +1,167 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.procedure;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HBaseTestingUtility;
+import org.apache.hadoop.hbase.StartMiniClusterOption;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.Admin;
+import org.apache.hadoop.hbase.client.ColumnFamilyDescriptorBuilder;
+import org.apache.hadoop.hbase.client.Put;
+import org.apache.hadoop.hbase.client.Table;
+import org.apache.hadoop.hbase.client.TableDescriptor;
+import org.apache.hadoop.hbase.client.TableDescriptorBuilder;
+import org.apache.hadoop.hbase.master.HMaster;
+import org.apache.hadoop.hbase.master.assignment.AssignmentManager;
+import org.apache.hadoop.hbase.procedure2.Procedure;
+import org.apache.hadoop.hbase.testclassification.MasterTests;
+import org.apache.hadoop.hbase.testclassification.MediumTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.metrics2.impl.JmxCacheBuster;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProcedureProtos.CreateTableState;
+
+@Category({ MasterTests.class, MediumTests.class })
+public class TestCreateTableNoRegionServer {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestCreateTableNoRegionServer.class);
+
+  private static final Logger LOG = LoggerFactory.getLogger(TestCreateTableNoRegionServer.class);
+
+  private static final HBaseTestingUtility UTIL = new HBaseTestingUtility();
+
+  private static TableName TABLE_NAME = TableName.valueOf("test");
+  
+  private static byte[] FAMILY = Bytes.toBytes("f1");
+
+  private static CountDownLatch ARRIVE;
+
+  private static CountDownLatch RESUME;
+
+  public static final class HMasterForTest extends HMaster {
+
+    public HMasterForTest(Configuration conf) throws IOException {
+      super(conf);
+    }
+
+    private boolean isInAssignRegionsState() {
+      try {
+        for (StackTraceElement e : Thread.currentThread().getStackTrace()) {
+          if (e.getClassName().equals(CreateTableProcedure.class.getName()) &&
+            e.getMethodName().equals("executeFromState")) {
+            for (Procedure<?> proc : getProcedures()) {
+              if (proc instanceof CreateTableProcedure && !proc.isFinished() &&
+                ((CreateTableProcedure) proc)
+                  .getCurrentStateId() == CreateTableState.CREATE_TABLE_ASSIGN_REGIONS_VALUE) {
+                return true;
+              }
+            }
+          }
+        }
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+      return false;
+    }
+
+    @Override
+    public AssignmentManager getAssignmentManager() {
+      if (ARRIVE != null && isInAssignRegionsState()) {
+        ARRIVE.countDown();
+        ARRIVE = null;
+        try {
+          RESUME.await();
+        } catch (InterruptedException e) {
+        }
+      }
+      return super.getAssignmentManager();
+    }
+  }
+
+  @BeforeClass
+  public static void setUp() throws Exception {
+    UTIL.startMiniCluster(
+      StartMiniClusterOption.builder().masterClass(HMasterForTest.class).build());
+    // this may cause dead lock if there is no live region server and want to start a new server.
+    // In JmxCacheBuster we will reinitialize the metrics system so it will get some metrics which
+    // will need to access meta, since there is no region server, the request will hang there for a
+    // long time while holding the lock of MetricsSystemImpl, but when start a new region server, we
+    // also need to update metrics in handleReportForDutyResponse, since we are all in the same
+    // process and uses the same metrics instance, we hit dead lock.
+    JmxCacheBuster.stop();
+  }
+
+  @AfterClass
+  public static void tearDown() throws Exception {
+    UTIL.shutdownMiniCluster();
+  }
+
+  @Test
+  public void testCreate() throws Exception {
+    TableDescriptor td = TableDescriptorBuilder.newBuilder(TABLE_NAME)
+      .setColumnFamily(ColumnFamilyDescriptorBuilder.of(FAMILY)).build();
+    Admin admin = UTIL.getAdmin();
+    ARRIVE = new CountDownLatch(1);
+    RESUME = new CountDownLatch(1);
+    Future<Void> future = admin.createTableAsync(td);
+    ARRIVE.await();
+
+    UTIL.getMiniHBaseCluster().stopRegionServer(0).join();
+
+    // make sure we the region server is done.
+    UTIL.waitFor(30000,
+      () -> UTIL.getMiniHBaseCluster().getMaster().getServerManager().getOnlineServers().isEmpty());
+    RESUME.countDown();
+
+    Thread.sleep(10000);
+    // the procedure should still be in the CREATE_TABLE_ASSIGN_REGIONS state, but here, we just
+    // warn it as it may cause more serious problem later.
+    for (Procedure<?> proc : UTIL.getMiniHBaseCluster().getMaster().getProcedures()) {
+      if (proc instanceof CreateTableProcedure && !proc.isFinished() &&
+        ((CreateTableProcedure) proc)
+          .getCurrentStateId() != CreateTableState.CREATE_TABLE_ASSIGN_REGIONS_VALUE) {
+        LOG.warn("Create table procedure {} assigned regions without a region server!", proc);
+      }
+    }
+    UTIL.getMiniHBaseCluster().startRegionServer();
+    // the creation should finally be done
+    future.get(30, TimeUnit.SECONDS);
+    // make sure we could put to the table
+    try (Table table = UTIL.getConnection().getTableBuilder(TABLE_NAME, null)
+      .setOperationTimeout(5000).build()) {
+      table.put(new Put(Bytes.toBytes(0)).addColumn(FAMILY,
+        Bytes.toBytes("q"), Bytes.toBytes(0)));
+    }
+  }
+}