HBASE-23604: Clarify AsyncRegistry usage in the code. (#957)

* HBASE-23604: Cleanup AsyncRegistry interface

- Cleans up the method names to make more sense and adds a little
more javadocs for context. In future patches we can revisit
the name of the actual class to make it more self explanatory.

- Does AsyncRegistry -> ConnectionRegistry rename.
"async" ness of the registry is kind of implicit based on
the interface contents and need not be reflected in the name.

Signed-off-by: Nick Dimiduk <ndimiduk@apache.org>
Signed-off-by: stack <stack@apache.org>
Signed-off-by: Viraj Jasani <vjasani@apache.org>

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncConnectionImpl.java

@@ -85,7 +85,7 @@ class AsyncConnectionImpl implements AsyncConnection {
 
   private final User user;
 
-  final AsyncRegistry registry;
+  final ConnectionRegistry registry;
 
   private final int rpcTimeout;
 
@@ -122,7 +122,7 @@ class AsyncConnectionImpl implements AsyncConnection {
 
   private volatile ConnectionOverAsyncConnection conn;
 
-  public AsyncConnectionImpl(Configuration conf, AsyncRegistry registry, String clusterId,
+  public AsyncConnectionImpl(Configuration conf, ConnectionRegistry registry, String clusterId,
       SocketAddress localAddress, User user) {
     this.conf = conf;
     this.user = user;
@@ -136,7 +136,8 @@ class AsyncConnectionImpl implements AsyncConnection {
     } else {
       this.metrics = Optional.empty();
     }
-    this.rpcClient = RpcClientFactory.createClient(conf, clusterId, localAddress, metrics.orElse(null));
+    this.rpcClient = RpcClientFactory.createClient(
+        conf, clusterId, localAddress, metrics.orElse(null));
     this.rpcControllerFactory = RpcControllerFactory.instantiate(conf);
     this.hostnameCanChange = conf.getBoolean(RESOLVE_HOSTNAME_ON_FAIL_KEY, true);
     this.rpcTimeout =
@@ -257,7 +258,7 @@ class AsyncConnectionImpl implements AsyncConnection {
   CompletableFuture<MasterService.Interface> getMasterStub() {
     return ConnectionUtils.getOrFetch(masterStub, masterStubMakeFuture, false, () -> {
       CompletableFuture<MasterService.Interface> future = new CompletableFuture<>();
-      addListener(registry.getMasterAddress(), (addr, error) -> {
+      addListener(registry.getActiveMaster(), (addr, error) -> {
         if (error != null) {
           future.completeExceptionally(error);
         } else if (addr == null) {
@@ -368,7 +369,7 @@ class AsyncConnectionImpl implements AsyncConnection {
   @Override
   public CompletableFuture<Hbck> getHbck() {
     CompletableFuture<Hbck> future = new CompletableFuture<>();
-    addListener(registry.getMasterAddress(), (sn, error) -> {
+    addListener(registry.getActiveMaster(), (sn, error) -> {
       if (error != null) {
         future.completeExceptionally(error);
       } else {

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncMetaRegionLocator.java

@@ -38,14 +38,14 @@ import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesti
 @InterfaceAudience.Private
 class AsyncMetaRegionLocator {
 
-  private final AsyncRegistry registry;
+  private final ConnectionRegistry registry;
 
   private final AtomicReference<RegionLocations> metaRegionLocations = new AtomicReference<>();
 
   private final AtomicReference<CompletableFuture<RegionLocations>> metaRelocateFuture =
     new AtomicReference<>();
 
-  AsyncMetaRegionLocator(AsyncRegistry registry) {
+  AsyncMetaRegionLocator(ConnectionRegistry registry) {
     this.registry = registry;
   }
 
@@ -60,7 +60,7 @@ class AsyncMetaRegionLocator {
    */
   CompletableFuture<RegionLocations> getRegionLocations(int replicaId, boolean reload) {
     return ConnectionUtils.getOrFetch(metaRegionLocations, metaRelocateFuture, reload,
-      registry::getMetaRegionLocation, locs -> isGood(locs, replicaId), "meta region location");
+      registry::getMetaRegionLocations, locs -> isGood(locs, replicaId), "meta region location");
   }
 
   private HRegionLocation getCacheLocation(HRegionLocation loc) {

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncTableRegionLocatorImpl.java

@@ -55,7 +55,7 @@ class AsyncTableRegionLocatorImpl implements AsyncTableRegionLocator {
   @Override
   public CompletableFuture<List<HRegionLocation>> getAllRegionLocations() {
     if (TableName.isMetaTableName(tableName)) {
-      return conn.registry.getMetaRegionLocation()
+      return conn.registry.getMetaRegionLocations()
         .thenApply(locs -> Arrays.asList(locs.getRegionLocations()));
     }
     return AsyncMetaTableAccessor.getTableHRegionLocations(conn.getTable(TableName.META_TABLE_NAME),

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionFactory.java

@@ -279,7 +279,7 @@ public class ConnectionFactory {
   public static CompletableFuture<AsyncConnection> createAsyncConnection(Configuration conf,
       final User user) {
     CompletableFuture<AsyncConnection> future = new CompletableFuture<>();
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(conf);
+    ConnectionRegistry registry = ConnectionRegistryFactory.getRegistry(conf);
     addListener(registry.getClusterId(), (clusterId, error) -> {
       if (error != null) {
         registry.close();

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistry.java

@@ -24,16 +24,17 @@ import org.apache.hadoop.hbase.ServerName;
 import org.apache.yetus.audience.InterfaceAudience;
 
 /**
- * Implementations hold cluster information such as this cluster's id, location of hbase:meta, etc..
+ * Registry for meta information needed for connection setup to a HBase cluster. Implementations
+ * hold cluster information such as this cluster's id, location of hbase:meta, etc..
  * Internal use only.
  */
 @InterfaceAudience.Private
-interface AsyncRegistry extends Closeable {
+interface ConnectionRegistry extends Closeable {
 
   /**
-   * Get the location of meta region.
+   * Get the location of meta region(s).
    */
-  CompletableFuture<RegionLocations> getMetaRegionLocation();
+  CompletableFuture<RegionLocations> getMetaRegionLocations();
 
   /**
    * Should only be called once.
@@ -43,9 +44,9 @@ interface AsyncRegistry extends Closeable {
   CompletableFuture<String> getClusterId();
 
   /**
-   * Get the address of HMaster.
+   * Get the address of active HMaster.
    */
-  CompletableFuture<ServerName> getMasterAddress();
+  CompletableFuture<ServerName> getActiveMaster();
 
   /**
    * Closes this instance and releases any system resources associated with it

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryFactory.java

@@ -1,4 +1,4 @@
-/**
+/*
  * 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
@@ -18,26 +18,28 @@
 package org.apache.hadoop.hbase.client;
 
 import org.apache.hadoop.conf.Configuration;
-import org.apache.yetus.audience.InterfaceAudience;
 import org.apache.hadoop.hbase.util.ReflectionUtils;
+import org.apache.yetus.audience.InterfaceAudience;
 
 /**
- * Get instance of configured Registry.
+ * Factory class to get the instance of configured connection registry.
  */
 @InterfaceAudience.Private
-final class AsyncRegistryFactory {
+final class ConnectionRegistryFactory {
 
-  static final String REGISTRY_IMPL_CONF_KEY = "hbase.client.registry.impl";
+  static final String CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY =
+      "hbase.client.connection.registry.impl";
 
-  private AsyncRegistryFactory() {
+  private ConnectionRegistryFactory() {
   }
 
   /**
-   * @return The cluster registry implementation to use.
+   * @return The connection registry implementation to use.
    */
-  static AsyncRegistry getRegistry(Configuration conf) {
+  static ConnectionRegistry getRegistry(Configuration conf) {
-    Class<? extends AsyncRegistry> clazz =
+    Class<? extends ConnectionRegistry> clazz = conf.getClass(
-        conf.getClass(REGISTRY_IMPL_CONF_KEY, ZKAsyncRegistry.class, AsyncRegistry.class);
+        CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY, ZKConnectionRegistry.class,
+        ConnectionRegistry.class);
     return ReflectionUtils.newInstance(clazz, conf);
   }
 }

hbase-client/src/main/java/org/apache/hadoop/hbase/client/RawAsyncHBaseAdmin.java

@@ -715,7 +715,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
   @Override
   public CompletableFuture<Boolean> isTableAvailable(TableName tableName) {
     if (TableName.isMetaTableName(tableName)) {
-      return connection.registry.getMetaRegionLocation().thenApply(locs -> Stream
+      return connection.registry.getMetaRegionLocations().thenApply(locs -> Stream
         .of(locs.getRegionLocations()).allMatch(loc -> loc != null && loc.getServerName() != null));
     }
     CompletableFuture<Boolean> future = new CompletableFuture<>();
@@ -853,7 +853,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
   @Override
   public CompletableFuture<List<RegionInfo>> getRegions(TableName tableName) {
     if (tableName.equals(META_TABLE_NAME)) {
-      return connection.registry.getMetaRegionLocation()
+      return connection.registry.getMetaRegionLocations()
         .thenApply(locs -> Stream.of(locs.getRegionLocations()).map(HRegionLocation::getRegion)
           .collect(Collectors.toList()));
     } else {
@@ -1081,8 +1081,9 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
     if (TableName.META_TABLE_NAME.equals(tableName)) {
       CompletableFuture<List<HRegionLocation>> future = new CompletableFuture<>();
       // For meta table, we use zk to fetch all locations.
-      AsyncRegistry registry = AsyncRegistryFactory.getRegistry(connection.getConfiguration());
+      ConnectionRegistry registry = ConnectionRegistryFactory.getRegistry(
-      addListener(registry.getMetaRegionLocation(), (metaRegions, err) -> {
+          connection.getConfiguration());
+      addListener(registry.getMetaRegionLocations(), (metaRegions, err) -> {
         if (err != null) {
           future.completeExceptionally(err);
         } else if (metaRegions == null || metaRegions.isEmpty() ||
@@ -1110,7 +1111,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
 
     switch (compactType) {
       case MOB:
-        addListener(connection.registry.getMasterAddress(), (serverName, err) -> {
+        addListener(connection.registry.getActiveMaster(), (serverName, err) -> {
           if (err != null) {
             future.completeExceptionally(err);
             return;
@@ -2349,7 +2350,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
         String encodedName = Bytes.toString(regionNameOrEncodedRegionName);
         if (encodedName.length() < RegionInfo.MD5_HEX_LENGTH) {
           // old format encodedName, should be meta region
-          future = connection.registry.getMetaRegionLocation()
+          future = connection.registry.getMetaRegionLocations()
             .thenApply(locs -> Stream.of(locs.getRegionLocations())
               .filter(loc -> loc.getRegion().getEncodedName().equals(encodedName)).findFirst());
         } else {
@@ -2360,7 +2361,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
         RegionInfo regionInfo =
           MetaTableAccessor.parseRegionInfoFromRegionName(regionNameOrEncodedRegionName);
         if (regionInfo.isMetaRegion()) {
-          future = connection.registry.getMetaRegionLocation()
+          future = connection.registry.getMetaRegionLocations()
             .thenApply(locs -> Stream.of(locs.getRegionLocations())
               .filter(loc -> loc.getRegion().getReplicaId() == regionInfo.getReplicaId())
               .findFirst());
@@ -2933,7 +2934,7 @@ class RawAsyncHBaseAdmin implements AsyncAdmin {
 
     switch (compactType) {
       case MOB:
-        addListener(connection.registry.getMasterAddress(), (serverName, err) -> {
+        addListener(connection.registry.getActiveMaster(), (serverName, err) -> {
           if (err != null) {
             future.completeExceptionally(err);
             return;

hbase-client/src/main/java/org/apache/hadoop/hbase/client/ZKConnectionRegistry.java

@@ -50,15 +50,15 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.ZooKeeperProtos;
  * Zookeeper based registry implementation.
  */
 @InterfaceAudience.Private
-class ZKAsyncRegistry implements AsyncRegistry {
+class ZKConnectionRegistry implements ConnectionRegistry {
 
-  private static final Logger LOG = LoggerFactory.getLogger(ZKAsyncRegistry.class);
+  private static final Logger LOG = LoggerFactory.getLogger(ZKConnectionRegistry.class);
 
   private final ReadOnlyZKClient zk;
 
   private final ZNodePaths znodePaths;
 
-  ZKAsyncRegistry(Configuration conf) {
+  ZKConnectionRegistry(Configuration conf) {
     this.znodePaths = new ZNodePaths(conf);
     this.zk = new ReadOnlyZKClient(conf);
   }
@@ -93,7 +93,7 @@ class ZKAsyncRegistry implements AsyncRegistry {
 
   @Override
   public CompletableFuture<String> getClusterId() {
-    return getAndConvert(znodePaths.clusterIdZNode, ZKAsyncRegistry::getClusterId);
+    return getAndConvert(znodePaths.clusterIdZNode, ZKConnectionRegistry::getClusterId);
   }
 
   @VisibleForTesting
@@ -144,7 +144,7 @@ class ZKAsyncRegistry implements AsyncRegistry {
       int replicaId = znodePaths.getMetaReplicaIdFromZnode(metaReplicaZNode);
       String path = ZNodePaths.joinZNode(znodePaths.baseZNode, metaReplicaZNode);
       if (replicaId == DEFAULT_REPLICA_ID) {
-        addListener(getAndConvert(path, ZKAsyncRegistry::getMetaProto), (proto, error) -> {
+        addListener(getAndConvert(path, ZKConnectionRegistry::getMetaProto), (proto, error) -> {
           if (error != null) {
             future.completeExceptionally(error);
             return;
@@ -162,7 +162,7 @@ class ZKAsyncRegistry implements AsyncRegistry {
           tryComplete(remaining, locs, future);
         });
       } else {
-        addListener(getAndConvert(path, ZKAsyncRegistry::getMetaProto), (proto, error) -> {
+        addListener(getAndConvert(path, ZKConnectionRegistry::getMetaProto), (proto, error) -> {
           if (future.isDone()) {
             return;
           }
@@ -191,7 +191,7 @@ class ZKAsyncRegistry implements AsyncRegistry {
   }
 
   @Override
-  public CompletableFuture<RegionLocations> getMetaRegionLocation() {
+  public CompletableFuture<RegionLocations> getMetaRegionLocations() {
     CompletableFuture<RegionLocations> future = new CompletableFuture<>();
     addListener(
       zk.list(znodePaths.baseZNode)
@@ -217,8 +217,8 @@ class ZKAsyncRegistry implements AsyncRegistry {
   }
 
   @Override
-  public CompletableFuture<ServerName> getMasterAddress() {
+  public CompletableFuture<ServerName> getActiveMaster() {
-    return getAndConvert(znodePaths.masterAddressZNode, ZKAsyncRegistry::getMasterProto)
+    return getAndConvert(znodePaths.masterAddressZNode, ZKConnectionRegistry::getMasterProto)
         .thenApply(proto -> {
           if (proto == null) {
             return null;

hbase-client/src/test/java/org/apache/hadoop/hbase/client/DoNothingConnectionRegistry.java

@@ -27,13 +27,13 @@ import org.apache.yetus.audience.InterfaceAudience;
  * Registry that does nothing. Otherwise, default Registry wants zookeeper up and running.
  */
 @InterfaceAudience.Private
-class DoNothingAsyncRegistry implements AsyncRegistry {
+class DoNothingConnectionRegistry implements ConnectionRegistry {
 
-  public DoNothingAsyncRegistry(Configuration conf) {
+  public DoNothingConnectionRegistry(Configuration conf) {
   }
 
   @Override
-  public CompletableFuture<RegionLocations> getMetaRegionLocation() {
+  public CompletableFuture<RegionLocations> getMetaRegionLocations() {
     return CompletableFuture.completedFuture(null);
   }
 
@@ -43,7 +43,7 @@ class DoNothingAsyncRegistry implements AsyncRegistry {
   }
 
   @Override
-  public CompletableFuture<ServerName> getMasterAddress() {
+  public CompletableFuture<ServerName> getActiveMaster() {
     return CompletableFuture.completedFuture(null);
   }
 

hbase-client/src/test/java/org/apache/hadoop/hbase/client/TestAsyncAdminRpcPriority.java

@@ -142,7 +142,7 @@ public class TestAsyncAdminRpcPriority {
     }).when(adminStub).stopServer(any(HBaseRpcController.class), any(StopServerRequest.class),
       any());
 
-    conn = new AsyncConnectionImpl(CONF, new DoNothingAsyncRegistry(CONF), "test", null,
+    conn = new AsyncConnectionImpl(CONF, new DoNothingConnectionRegistry(CONF), "test", null,
       UserProvider.instantiate(CONF).getCurrent()) {
 
       @Override

hbase-client/src/test/java/org/apache/hadoop/hbase/client/TestAsyncMetaRegionLocatorFailFast.java

@@ -1,4 +1,4 @@
-/**
+/*
  * 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
@@ -43,21 +43,21 @@ public class TestAsyncMetaRegionLocatorFailFast {
 
   private static AsyncMetaRegionLocator LOCATOR;
 
-  private static final class FaultyAsyncRegistry extends DoNothingAsyncRegistry {
+  private static final class FaultyConnectionRegistry extends DoNothingConnectionRegistry {
 
-    public FaultyAsyncRegistry(Configuration conf) {
+    public FaultyConnectionRegistry(Configuration conf) {
       super(conf);
     }
 
     @Override
-    public CompletableFuture<RegionLocations> getMetaRegionLocation() {
+    public CompletableFuture<RegionLocations> getMetaRegionLocations() {
       return FutureUtils.failedFuture(new DoNotRetryRegionException("inject error"));
     }
   }
 
   @BeforeClass
   public static void setUp() {
-    LOCATOR = new AsyncMetaRegionLocator(new FaultyAsyncRegistry(CONF));
+    LOCATOR = new AsyncMetaRegionLocator(new FaultyConnectionRegistry(CONF));
   }
 
   @Test(expected = DoNotRetryIOException.class)

hbase-client/src/test/java/org/apache/hadoop/hbase/client/TestAsyncTableRpcPriority.java

@@ -175,7 +175,7 @@ public class TestAsyncTableRpcPriority {
         return null;
       }
     }).when(stub).get(any(HBaseRpcController.class), any(GetRequest.class), any());
-    conn = new AsyncConnectionImpl(CONF, new DoNothingAsyncRegistry(CONF), "test", null,
+    conn = new AsyncConnectionImpl(CONF, new DoNothingConnectionRegistry(CONF), "test", null,
       UserProvider.instantiate(CONF).getCurrent()) {
 
       @Override

hbase-client/src/test/java/org/apache/hadoop/hbase/client/TestConnectionRegistryLeak.java

@@ -38,17 +38,17 @@ import org.junit.Test;
 import org.junit.experimental.categories.Category;
 
 @Category({ ClientTests.class, SmallTests.class })
-public class TestAsyncRegistryLeak {
+public class TestConnectionRegistryLeak {
 
   @ClassRule
   public static final HBaseClassTestRule CLASS_RULE =
-    HBaseClassTestRule.forClass(TestAsyncRegistryLeak.class);
+    HBaseClassTestRule.forClass(TestConnectionRegistryLeak.class);
 
-  public static final class AsyncRegistryForTest extends DoNothingAsyncRegistry {
+  public static final class ConnectionRegistryForTest extends DoNothingConnectionRegistry {
 
     private boolean closed = false;
 
-    public AsyncRegistryForTest(Configuration conf) {
+    public ConnectionRegistryForTest(Configuration conf) {
       super(conf);
       CREATED.add(this);
     }
@@ -64,14 +64,14 @@ public class TestAsyncRegistryLeak {
     }
   }
 
-  private static final List<AsyncRegistryForTest> CREATED = new ArrayList<>();
+  private static final List<ConnectionRegistryForTest> CREATED = new ArrayList<>();
 
   private static Configuration CONF = HBaseConfiguration.create();
 
   @BeforeClass
   public static void setUp() {
-    CONF.setClass(AsyncRegistryFactory.REGISTRY_IMPL_CONF_KEY, AsyncRegistryForTest.class,
+    CONF.setClass(ConnectionRegistryFactory.CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY,
-      AsyncRegistry.class);
+        ConnectionRegistryForTest.class, ConnectionRegistry.class);
   }
 
   @Test

hbase-server/src/main/java/org/apache/hadoop/hbase/client/AsyncClusterConnectionImpl.java

@@ -50,8 +50,8 @@ import org.apache.hadoop.hbase.shaded.protobuf.generated.HBaseProtos.RegionSpeci
 @InterfaceAudience.Private
 class AsyncClusterConnectionImpl extends AsyncConnectionImpl implements AsyncClusterConnection {
 
-  public AsyncClusterConnectionImpl(Configuration conf, AsyncRegistry registry, String clusterId,
+  public AsyncClusterConnectionImpl(Configuration conf, ConnectionRegistry registry,
-      SocketAddress localAddress, User user) {
+      String clusterId, SocketAddress localAddress, User user) {
     super(conf, registry, clusterId, localAddress, user);
   }
 

hbase-server/src/main/java/org/apache/hadoop/hbase/client/ClusterConnectionFactory.java

@@ -49,7 +49,7 @@ public final class ClusterConnectionFactory {
    */
   public static AsyncClusterConnection createAsyncClusterConnection(Configuration conf,
       SocketAddress localAddress, User user) throws IOException {
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(conf);
+    ConnectionRegistry registry = ConnectionRegistryFactory.getRegistry(conf);
     String clusterId = FutureUtils.get(registry.getClusterId());
     Class<? extends AsyncClusterConnection> clazz =
       conf.getClass(HBASE_SERVER_CLUSTER_CONNECTION_IMPL, AsyncClusterConnectionImpl.class,

hbase-server/src/test/java/org/apache/hadoop/hbase/backup/example/TestZooKeeperTableArchiveClient.java

@@ -21,7 +21,6 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
-
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
@@ -40,7 +39,7 @@ import org.apache.hadoop.hbase.client.ColumnFamilyDescriptor;
 import org.apache.hadoop.hbase.client.ColumnFamilyDescriptorBuilder;
 import org.apache.hadoop.hbase.client.Connection;
 import org.apache.hadoop.hbase.client.ConnectionFactory;
-import org.apache.hadoop.hbase.client.DummyAsyncRegistry;
+import org.apache.hadoop.hbase.client.DummyConnectionRegistry;
 import org.apache.hadoop.hbase.client.Put;
 import org.apache.hadoop.hbase.master.cleaner.BaseHFileCleanerDelegate;
 import org.apache.hadoop.hbase.master.cleaner.DirScanPool;
@@ -92,7 +91,7 @@ public class TestZooKeeperTableArchiveClient {
   private static RegionServerServices rss;
   private static DirScanPool POOL;
 
-  public static final class MockRegistry extends DummyAsyncRegistry {
+  public static final class MockRegistry extends DummyConnectionRegistry {
 
     public MockRegistry(Configuration conf) {
     }
@@ -110,8 +109,8 @@ public class TestZooKeeperTableArchiveClient {
   public static void setupCluster() throws Exception {
     setupConf(UTIL.getConfiguration());
     UTIL.startMiniZKCluster();
-    UTIL.getConfiguration().setClass("hbase.client.registry.impl", MockRegistry.class,
+    UTIL.getConfiguration().setClass(MockRegistry.REGISTRY_IMPL_CONF_KEY, MockRegistry.class,
-      DummyAsyncRegistry.class);
+      DummyConnectionRegistry.class);
     CONNECTION = ConnectionFactory.createConnection(UTIL.getConfiguration());
     archivingClient = new ZKTableArchiveClient(UTIL.getConfiguration(), CONNECTION);
     // make hfile archiving node so we can archive files
@@ -147,9 +146,13 @@ public class TestZooKeeperTableArchiveClient {
 
   @AfterClass
   public static void cleanupTest() throws Exception {
-    CONNECTION.close();
+    if (CONNECTION != null) {
+      CONNECTION.close();
+    }
     UTIL.shutdownMiniZKCluster();
-    POOL.shutdownNow();
+    if (POOL != null) {
+      POOL.shutdownNow();
+    }
   }
 
   /**
@@ -353,6 +356,7 @@ public class TestZooKeeperTableArchiveClient {
    * @throws IOException on failure
    * @throws KeeperException on failure
    */
+  @SuppressWarnings("checkstyle:EmptyBlock")
   private List<BaseHFileCleanerDelegate> turnOnArchiving(String tableName, HFileCleaner cleaner)
       throws IOException, KeeperException {
     // turn on hfile retention

hbase-server/src/test/java/org/apache/hadoop/hbase/client/AbstractTestRegionLocator.java

@@ -58,7 +58,8 @@ public abstract class AbstractTestRegionLocator {
     }
     UTIL.getAdmin().createTable(td, SPLIT_KEYS);
     UTIL.waitTableAvailable(TABLE_NAME);
-    try (AsyncRegistry registry = AsyncRegistryFactory.getRegistry(UTIL.getConfiguration())) {
+    try (ConnectionRegistry registry =
+             ConnectionRegistryFactory.getRegistry(UTIL.getConfiguration())) {
       RegionReplicaTestHelper.waitUntilAllMetaReplicasHavingRegionLocation(UTIL.getConfiguration(),
         registry, REGION_REPLICATION);
     }

hbase-server/src/test/java/org/apache/hadoop/hbase/client/DummyConnectionRegistry.java

@@ -23,14 +23,15 @@ import org.apache.hadoop.hbase.ServerName;
 
 /**
  * Can be overridden in UT if you only want to implement part of the methods in
- * {@link AsyncRegistry}.
+ * {@link ConnectionRegistry}.
  */
-public class DummyAsyncRegistry implements AsyncRegistry {
+public class DummyConnectionRegistry implements ConnectionRegistry {
 
-  public static final String REGISTRY_IMPL_CONF_KEY = AsyncRegistryFactory.REGISTRY_IMPL_CONF_KEY;
+  public static final String REGISTRY_IMPL_CONF_KEY =
+      ConnectionRegistryFactory.CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY;
 
   @Override
-  public CompletableFuture<RegionLocations> getMetaRegionLocation() {
+  public CompletableFuture<RegionLocations> getMetaRegionLocations() {
     return null;
   }
 
@@ -40,7 +41,7 @@ public class DummyAsyncRegistry implements AsyncRegistry {
   }
 
   @Override
-  public CompletableFuture<ServerName> getMasterAddress() {
+  public CompletableFuture<ServerName> getActiveMaster() {
     return null;
   }
 

hbase-server/src/test/java/org/apache/hadoop/hbase/client/RegionReplicaTestHelper.java

@@ -44,7 +44,7 @@ public final class RegionReplicaTestHelper {
 
   // waits for all replicas to have region location
   static void waitUntilAllMetaReplicasHavingRegionLocation(Configuration conf,
-      AsyncRegistry registry, int regionReplication) throws IOException {
+      ConnectionRegistry registry, int regionReplication) throws IOException {
     Waiter.waitFor(conf, conf.getLong("hbase.client.sync.wait.timeout.msec", 60000), 200, true,
       new ExplainingPredicate<IOException>() {
         @Override
@@ -55,7 +55,7 @@ public final class RegionReplicaTestHelper {
         @Override
         public boolean evaluate() throws IOException {
           try {
-            RegionLocations locs = registry.getMetaRegionLocation().get();
+            RegionLocations locs = registry.getMetaRegionLocations().get();
             if (locs.size() < regionReplication) {
               return false;
             }
@@ -66,7 +66,7 @@ public final class RegionReplicaTestHelper {
             }
             return true;
           } catch (Exception e) {
-            TestZKAsyncRegistry.LOG.warn("Failed to get meta region locations", e);
+            TestZKConnectionRegistry.LOG.warn("Failed to get meta region locations", e);
             return false;
           }
         }

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncAdminWithRegionReplicas.java

@@ -53,7 +53,8 @@ public class TestAsyncAdminWithRegionReplicas extends TestAsyncAdminBase {
   public static void setUpBeforeClass() throws Exception {
     TEST_UTIL.getConfiguration().setInt(HConstants.META_REPLICAS_NUM, 3);
     TestAsyncAdminBase.setUpBeforeClass();
-    try (AsyncRegistry registry = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration())) {
+    try (ConnectionRegistry registry =
+             ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration())) {
       RegionReplicaTestHelper
         .waitUntilAllMetaReplicasHavingRegionLocation(TEST_UTIL.getConfiguration(), registry, 3);
     }

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncMetaRegionLocator.java

@@ -44,7 +44,7 @@ public class TestAsyncMetaRegionLocator {
 
   private static final HBaseTestingUtility TEST_UTIL = new HBaseTestingUtility();
 
-  private static AsyncRegistry REGISTRY;
+  private static ConnectionRegistry REGISTRY;
 
   private static AsyncMetaRegionLocator LOCATOR;
 
@@ -53,7 +53,7 @@ public class TestAsyncMetaRegionLocator {
     TEST_UTIL.getConfiguration().setInt(HConstants.META_REPLICAS_NUM, 3);
     TEST_UTIL.startMiniCluster(3);
     TEST_UTIL.waitUntilNoRegionsInTransition();
-    REGISTRY = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    REGISTRY = ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     RegionReplicaTestHelper
       .waitUntilAllMetaReplicasHavingRegionLocation(TEST_UTIL.getConfiguration(), REGISTRY, 3);
     TEST_UTIL.getAdmin().balancerSwitch(false, true);

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncNonMetaRegionLocator.java

@@ -79,7 +79,8 @@ public class TestAsyncNonMetaRegionLocator {
   public static void setUp() throws Exception {
     TEST_UTIL.startMiniCluster(3);
     TEST_UTIL.getAdmin().balancerSwitch(false, true);
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    ConnectionRegistry registry =
+        ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     CONN = new AsyncConnectionImpl(TEST_UTIL.getConfiguration(), registry,
       registry.getClusterId().get(), null, User.getCurrent());
     LOCATOR = new AsyncNonMetaRegionLocator(CONN);

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncNonMetaRegionLocatorConcurrenyLimit.java

@@ -123,7 +123,8 @@ public class TestAsyncNonMetaRegionLocatorConcurrenyLimit {
     conf.setInt(MAX_CONCURRENT_LOCATE_REQUEST_PER_TABLE, MAX_ALLOWED);
     TEST_UTIL.startMiniCluster(3);
     TEST_UTIL.getAdmin().balancerSwitch(false, true);
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    ConnectionRegistry registry =
+        ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     CONN = new AsyncConnectionImpl(TEST_UTIL.getConfiguration(), registry,
       registry.getClusterId().get(), null, User.getCurrent());
     LOCATOR = new AsyncNonMetaRegionLocator(CONN);

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncRegionLocator.java

@@ -98,7 +98,8 @@ public class TestAsyncRegionLocator {
     TEST_UTIL.startMiniCluster(1);
     TEST_UTIL.createTable(TABLE_NAME, FAMILY);
     TEST_UTIL.waitTableAvailable(TABLE_NAME);
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    ConnectionRegistry registry =
+        ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     CONN = new AsyncConnectionImpl(TEST_UTIL.getConfiguration(), registry,
       registry.getClusterId().get(), null, User.getCurrent());
     LOCATOR = CONN.getLocator();

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncSingleRequestRpcRetryingCaller.java

@@ -71,7 +71,8 @@ public class TestAsyncSingleRequestRpcRetryingCaller {
     TEST_UTIL.getAdmin().balancerSwitch(false, true);
     TEST_UTIL.createTable(TABLE_NAME, FAMILY);
     TEST_UTIL.waitTableAvailable(TABLE_NAME);
-    AsyncRegistry registry = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    ConnectionRegistry registry =
+        ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     CONN = new AsyncConnectionImpl(TEST_UTIL.getConfiguration(), registry,
       registry.getClusterId().get(), null, User.getCurrent());
   }

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestAsyncTableUseMetaReplicas.java

@@ -91,7 +91,7 @@ public class TestAsyncTableUseMetaReplicas {
     conf.setStrings(CoprocessorHost.REGION_COPROCESSOR_CONF_KEY,
       FailPrimaryMetaScanCp.class.getName());
     UTIL.startMiniCluster(3);
-    try (AsyncRegistry registry = AsyncRegistryFactory.getRegistry(conf)) {
+    try (ConnectionRegistry registry = ConnectionRegistryFactory.getRegistry(conf)) {
       RegionReplicaTestHelper.waitUntilAllMetaReplicasHavingRegionLocation(conf, registry, 3);
     }
     try (Table table = UTIL.createTable(TABLE_NAME, FAMILY)) {

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestMetaRegionLocationCache.java

@@ -53,13 +53,13 @@ public class TestMetaRegionLocationCache {
       HBaseClassTestRule.forClass(TestMetaRegionLocationCache.class);
 
   private static final HBaseTestingUtility TEST_UTIL = new HBaseTestingUtility();
-  private static AsyncRegistry REGISTRY;
+  private static ConnectionRegistry REGISTRY;
 
   @BeforeClass
   public static void setUp() throws Exception {
     TEST_UTIL.getConfiguration().setInt(HConstants.META_REPLICAS_NUM, 3);
     TEST_UTIL.startMiniCluster(3);
-    REGISTRY = AsyncRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
+    REGISTRY = ConnectionRegistryFactory.getRegistry(TEST_UTIL.getConfiguration());
     RegionReplicaTestHelper.waitUntilAllMetaReplicasHavingRegionLocation(
         TEST_UTIL.getConfiguration(), REGISTRY, 3);
     TEST_UTIL.getAdmin().balancerSwitch(false, true);

hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestZKConnectionRegistry.java

@@ -48,16 +48,16 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 @Category({ MediumTests.class, ClientTests.class })
-public class TestZKAsyncRegistry {
+public class TestZKConnectionRegistry {
 
   @ClassRule
   public static final HBaseClassTestRule CLASS_RULE =
-    HBaseClassTestRule.forClass(TestZKAsyncRegistry.class);
+    HBaseClassTestRule.forClass(TestZKConnectionRegistry.class);
 
-  static final Logger LOG = LoggerFactory.getLogger(TestZKAsyncRegistry.class);
+  static final Logger LOG = LoggerFactory.getLogger(TestZKConnectionRegistry.class);
   static final HBaseTestingUtility TEST_UTIL = new HBaseTestingUtility();
 
-  private static ZKAsyncRegistry REGISTRY;
+  private static ZKConnectionRegistry REGISTRY;
 
   @BeforeClass
   public static void setUp() throws Exception {
@@ -67,7 +67,7 @@ public class TestZKAsyncRegistry {
     // make sure that we do not depend on this config when getting locations for meta replicas, see
     // HBASE-21658.
     conf.setInt(META_REPLICAS_NUM, 1);
-    REGISTRY = new ZKAsyncRegistry(conf);
+    REGISTRY = new ZKConnectionRegistry(conf);
   }
 
   @AfterClass
@@ -84,10 +84,10 @@ public class TestZKAsyncRegistry {
     assertEquals("Expected " + expectedClusterId + ", found=" + clusterId, expectedClusterId,
       clusterId);
     assertEquals(TEST_UTIL.getHBaseCluster().getMaster().getServerName(),
-      REGISTRY.getMasterAddress().get());
+      REGISTRY.getActiveMaster().get());
     RegionReplicaTestHelper
       .waitUntilAllMetaReplicasHavingRegionLocation(TEST_UTIL.getConfiguration(), REGISTRY, 3);
-    RegionLocations locs = REGISTRY.getMetaRegionLocation().get();
+    RegionLocations locs = REGISTRY.getMetaRegionLocations().get();
     assertEquals(3, locs.getRegionLocations().length);
     IntStream.range(0, 3).forEach(i -> {
       HRegionLocation loc = locs.getRegionLocation(i);
@@ -102,7 +102,7 @@ public class TestZKAsyncRegistry {
     try (ReadOnlyZKClient zk1 = REGISTRY.getZKClient()) {
       Configuration otherConf = new Configuration(TEST_UTIL.getConfiguration());
       otherConf.set(HConstants.ZOOKEEPER_QUORUM, "localhost");
-      try (ZKAsyncRegistry otherRegistry = new ZKAsyncRegistry(otherConf)) {
+      try (ZKConnectionRegistry otherRegistry = new ZKConnectionRegistry(otherConf)) {
         ReadOnlyZKClient zk2 = otherRegistry.getZKClient();
         assertNotSame("Using a different configuration / quorum should result in different " +
           "backing zk connection.", zk1, zk2);
@@ -119,9 +119,9 @@ public class TestZKAsyncRegistry {
   public void testNoMetaAvailable() throws InterruptedException {
     Configuration conf = new Configuration(TEST_UTIL.getConfiguration());
     conf.set("zookeeper.znode.metaserver", "whatever");
-    try (ZKAsyncRegistry registry = new ZKAsyncRegistry(conf)) {
+    try (ZKConnectionRegistry registry = new ZKConnectionRegistry(conf)) {
       try {
-        registry.getMetaRegionLocation().get();
+        registry.getMetaRegionLocations().get();
         fail("Should have failed since we set an incorrect meta znode prefix");
       } catch (ExecutionException e) {
         assertThat(e.getCause(), instanceOf(IOException.class));

hbase-server/src/test/java/org/apache/hadoop/hbase/replication/regionserver/TestWALEntrySinkFilter.java

@@ -1,4 +1,4 @@
-/**
+/*
  * 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
@@ -19,7 +19,6 @@ package org.apache.hadoop.hbase.replication.regionserver;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
-
 import java.io.IOException;
 import java.net.SocketAddress;
 import java.util.ArrayList;
@@ -43,8 +42,8 @@ import org.apache.hadoop.hbase.client.AsyncConnection;
 import org.apache.hadoop.hbase.client.AsyncTable;
 import org.apache.hadoop.hbase.client.ClusterConnectionFactory;
 import org.apache.hadoop.hbase.client.DummyAsyncClusterConnection;
-import org.apache.hadoop.hbase.client.DummyAsyncRegistry;
 import org.apache.hadoop.hbase.client.DummyAsyncTable;
+import org.apache.hadoop.hbase.client.DummyConnectionRegistry;
 import org.apache.hadoop.hbase.client.Row;
 import org.apache.hadoop.hbase.security.User;
 import org.apache.hadoop.hbase.testclassification.ReplicationTests;
@@ -57,9 +56,7 @@ import org.junit.experimental.categories.Category;
 import org.junit.rules.TestName;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.apache.hbase.thirdparty.com.google.protobuf.ByteString;
-
 import org.apache.hadoop.hbase.shaded.protobuf.generated.AdminProtos;
 
 /**
@@ -108,12 +105,12 @@ public class TestWALEntrySinkFilter {
   public void testWALEntryFilter() throws IOException {
     Configuration conf = HBaseConfiguration.create();
     // Make it so our filter is instantiated on construction of ReplicationSink.
-    conf.setClass(DummyAsyncRegistry.REGISTRY_IMPL_CONF_KEY, DevNullAsyncRegistry.class,
+    conf.setClass(DummyConnectionRegistry.REGISTRY_IMPL_CONF_KEY, DevNullConnectionRegistry.class,
-      DummyAsyncRegistry.class);
+        DummyConnectionRegistry.class);
     conf.setClass(WALEntrySinkFilter.WAL_ENTRY_FILTER_KEY,
-      IfTimeIsGreaterThanBOUNDARYWALEntrySinkFilterImpl.class, WALEntrySinkFilter.class);
+        IfTimeIsGreaterThanBOUNDARYWALEntrySinkFilterImpl.class, WALEntrySinkFilter.class);
     conf.setClass(ClusterConnectionFactory.HBASE_SERVER_CLUSTER_CONNECTION_IMPL,
-      DevNullAsyncClusterConnection.class, AsyncClusterConnection.class);
+        DevNullAsyncClusterConnection.class, AsyncClusterConnection.class);
     ReplicationSink sink = new ReplicationSink(conf, STOPPABLE);
     // Create some dumb walentries.
     List<AdminProtos.WALEntry> entries = new ArrayList<>();
@@ -190,9 +187,9 @@ public class TestWALEntrySinkFilter {
     }
   }
 
-  public static class DevNullAsyncRegistry extends DummyAsyncRegistry {
+  public static class DevNullConnectionRegistry extends DummyConnectionRegistry {
 
-    public DevNullAsyncRegistry(Configuration conf) {
+    public DevNullConnectionRegistry(Configuration conf) {
     }
 
     @Override