ThriftClientProvider.java

/*
 * Copyright © 2012-2014 Cask Data, Inc.
 *
 * Licensed 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 co.cask.tephra.distributed;

import org.apache.thrift.TException;

import java.util.concurrent.TimeoutException;

/**
 * This interface is used to provide thrift tx service clients:
 * there is only one (singleton)
 * tx service per JVM, but many threads may use it concurrently.
 * However, being a thrift client, it is not thread-safe. In
 * order to avoid serializing all tx calls by synchronizing
 * on the tx service client, we employ a pool of clients. But
 * in different scenarios there are different strategies for
 * pooling: If there are many short-lived threads, it is wise
 * to have a shared pool between all threads. But if there are
 * few long-lived threads, it may be better to have thread-local
 * client for each thread.
 *
 * This interface provides an abstraction of the pooling strategy.
 */
public interface ThriftClientProvider {

  /**
   * Initialize the provider. At this point, it should be verified
   * that tx service is up and running and getClient() can
   * create new clients when necessary.
   */
  void initialize() throws TException;

  /**
   * Retrieve an AutoCloseable wrapper around  tx client for exclusive use by the
   * current thread. The client must be closed (returned) to the provider after use.
   * @return an tx client, connected and fully functional
   */
  CloseableThriftClient getCloseableClient() throws TException,
    TimeoutException, InterruptedException;

  /**
   * Release an tx client back to the provider's pool, if the client is valid.
   * If the client becomes disfunctional, for instance, due to a socket
   * exception. The provider must make sure to close the client, and it
   * must remove the client from its arsenal and be prepared to create
   * a new client subsequently.
   *
   * @param client The client to return
   */
  void returnClient(TransactionServiceThriftClient client);
}