/**
    *
    * 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.client;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.concurrent.ExecutorService;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.Abortable;
  import org.apache.hadoop.hbase.TableName;
  
  /**
   * A cluster connection encapsulating lower level individual connections to actual servers and
   * a connection to zookeeper. Connections are instantiated through the {@link ConnectionFactory}
   * class. The lifecycle of the connection is managed by the caller, who has to {@link #close()}
   * the connection to release the resources.
   *
   * <p> The connection object contains logic to find the master, locate regions out on the cluster,
   * keeps a cache of locations and then knows how to re-calibrate after they move. The individual
   * connections to servers, meta cache, zookeeper connection, etc are all shared by the
   * {@link Table} and {@link Admin} instances obtained from this connection.
   *
   * <p> Connection creation is a heavy-weight operation. Connection implementations are thread-safe,
   * so that the client can create a connection once, and share it with different threads.
   * {@link Table} and {@link Admin} instances, on the other hand, are light-weight and are not
   * thread-safe.  Typically, a single connection per client application is instantiated and every
   * thread will obtain its own Table instance. Caching or pooling of {@link Table} and {@link Admin}
   * is not recommended.
   *
   * <p>This class replaces {@link HConnection}, which is now deprecated.
   * @see ConnectionFactory
   * @since 0.99.0
   */
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public interface Connection extends Abortable, Closeable {
  
    /*
     * Implementation notes:
     *  - Only allow new style of interfaces:
     *   -- All table names are passed as TableName. No more byte[] and string arguments
     *   -- Most of the classes with names H is deprecated in favor of non-H versions
     *   (Table, Connection vs HConnection, etc)
     *   -- Only real client-facing public methods are allowed
     *  - Connection should contain only getTable(), getAdmin() kind of general methods.
     */
  
    /**
     * @return Configuration instance being used by this Connection instance.
     */
    Configuration getConfiguration();
  
    /**
     * Retrieve a Table implementation for accessing a table.
     * The returned Table is not thread safe, a new instance should be created for each using thread.
     * This is a lightweight operation, pooling or caching of the returned Table
     * is neither required nor desired.
     * <p>
     * The caller is responsible for calling {@link Table#close()} on the returned
     * table instance.
     * <p>
     * Since 0.98.1 this method no longer checks table existence. An exception
     * will be thrown if the table does not exist only when the first operation is
     * attempted.
     * @param tableName the name of the table
     * @return a Table to use for interactions with this table
     */
    Table getTable(TableName tableName) throws IOException;
  
    /**
     * Retrieve a Table implementation for accessing a table.
     * The returned Table is not thread safe, a new instance should be created for each using thread.
     * This is a lightweight operation, pooling or caching of the returned Table
     * is neither required nor desired.
     * <p>
     * The caller is responsible for calling {@link Table#close()} on the returned
     * table instance.
     * <p>
     * Since 0.98.1 this method no longer checks table existence. An exception
     * will be thrown if the table does not exist only when the first operation is
    * attempted.
    *
    * @param tableName the name of the table
    * @param pool The thread pool to use for batch operations, null to use a default pool.
    * @return a Table to use for interactions with this table
    */
   Table getTable(TableName tableName, ExecutorService pool)  throws IOException;
 
   /**
    * <p>
    * Retrieve a {@link BufferedMutator} for performing client-side buffering of writes. The
    * {@link BufferedMutator} returned by this method is thread-safe. This BufferedMutator will
    * use the Connection's ExecutorService. This object can be used for long lived operations.
    * </p>
    * <p>
    * The caller is responsible for calling {@link BufferedMutator#close()} on
    * the returned {@link BufferedMutator} instance.
    * </p>
    * <p>
    * This accessor will use the connection's ExecutorService and will throw an
    * exception in the main thread when an asynchronous exception occurs.
    *
    * @param tableName the name of the table
    *
    * @return a {@link BufferedMutator} for the supplied tableName.
    */
   public BufferedMutator getBufferedMutator(TableName tableName) throws IOException;
 
   /**
    * Retrieve a {@link BufferedMutator} for performing client-side buffering of writes. The
    * {@link BufferedMutator} returned by this method is thread-safe. This object can be used for
    * long lived table operations. The caller is responsible for calling
    * {@link BufferedMutator#close()} on the returned {@link BufferedMutator} instance.
    *
    * @param params details on how to instantiate the {@code BufferedMutator}.
    * @return a {@link BufferedMutator} for the supplied tableName.
    */
   public BufferedMutator getBufferedMutator(BufferedMutatorParams params) throws IOException;
 
   /**
    * Retrieve a RegionLocator implementation to inspect region information on a table. The returned
    * RegionLocator is not thread-safe, so a new instance should be created for each using thread.
    *
    * This is a lightweight operation.  Pooling or caching of the returned RegionLocator is neither
    * required nor desired.
    * <br>
    * The caller is responsible for calling {@link RegionLocator#close()} on the returned
    * RegionLocator instance.
    *
    * RegionLocator needs to be unmanaged
    *
    * @param tableName Name of the table who's region is to be examined
    * @return A RegionLocator instance
    */
   public RegionLocator getRegionLocator(TableName tableName) throws IOException;
 
   /**
    * Retrieve an Admin implementation to administer an HBase cluster.
    * The returned Admin is not guaranteed to be thread-safe.  A new instance should be created for
    * each using thread.  This is a lightweight operation.  Pooling or caching of the returned
    * Admin is not recommended.
    * <br>
    * The caller is responsible for calling {@link Admin#close()} on the returned
    * Admin instance.
    *
    * @return an Admin instance for cluster administration
    */
   Admin getAdmin() throws IOException;
 
   @Override
   public void close() throws IOException;
 
   /**
    * Returns whether the connection is closed or not.
    * @return true if this connection is closed
    */
   boolean isClosed();
 }