/**
 * 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.hdfs.storageservice.server;

import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdfs.storageservice.Response;
import org.apache.hadoop.hdfs.storageservice.server.NameNodeHandler.RequestCallable;

import java.io.Closeable;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/** Handles request execution, manages throttling and reordering */
class RequestCallableExecutor implements Closeable {
  private final BlockingQueue<Runnable> requestsQueue;
  private final ThreadPoolExecutor underlyingExecutor;
  private final ListeningExecutorService callExecutor;

  public RequestCallableExecutor(Configuration con) {
    requestsQueue = new SynchronousQueue<Runnable>();
    // TODO: this needs to be scalable and externally configurable
    underlyingExecutor = new ThreadPoolExecutor(1, 1, 1L, TimeUnit.SECONDS, requestsQueue);
    callExecutor = MoreExecutors.listeningDecorator(underlyingExecutor);
  }

  @Override
  public void close() {
    underlyingExecutor.shutdown();
  }

  public <T> Response<T> submit(RequestCallable<T> requestCallable) {
    return new Response<T>(callExecutor.submit(requestCallable));
  }
}