content: /**
   * 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.activemq.transport.nio;
  
  import java.io.IOException;
  import java.nio.channels.spi.AbstractSelectableChannel;
  import java.util.LinkedList;
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.Executor;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.RejectedExecutionHandler;
  import java.util.concurrent.SynchronousQueue;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  
  /**
   * The SelectorManager will manage one Selector and the thread that checks the
   * selector.
   *
   * We may need to consider running more than one thread to check the selector if
   * servicing the selector takes too long.
   */
  public final class SelectorManager {
  
      public static final SelectorManager SINGLETON = new SelectorManager();
  
      private Executor selectorExecutor = createDefaultExecutor();
      private Executor channelExecutor = selectorExecutor;
      private final LinkedList<SelectorWorker> freeWorkers = new LinkedList<SelectorWorker>();
      private int maxChannelsPerWorker = -1;
  
      protected ExecutorService createDefaultExecutor() {
          ThreadPoolExecutor rc = new ThreadPoolExecutor(getDefaultCorePoolSize(), getDefaultMaximumPoolSize(), getDefaultKeepAliveTime(), TimeUnit.SECONDS, newWorkQueue(),
              new ThreadFactory() {
  
                  private long i = 0;
  
                  @Override
                  public Thread newThread(Runnable runnable) {
                      Thread t = new Thread(runnable, "ActiveMQ NIO Worker " + (i++));
                      t.setDaemon(true);
                      return t;
                  }
              }, newRejectionHandler());
  
          return rc;
      }
  
      private RejectedExecutionHandler newRejectionHandler() {
          return canRejectWork() ? new ThreadPoolExecutor.AbortPolicy() : new ThreadPoolExecutor.CallerRunsPolicy();
      }
  
      private BlockingQueue<Runnable> newWorkQueue() {
          final int workQueueCapicity = getDefaultWorkQueueCapacity();
          return workQueueCapicity > 0 ? new LinkedBlockingQueue<Runnable>(workQueueCapicity) : new SynchronousQueue<Runnable>();
      }
  
      private static boolean canRejectWork() {
          return Boolean.getBoolean("org.apache.activemq.transport.nio.SelectorManager.rejectWork");
      }
  
      private static int getDefaultWorkQueueCapacity() {
          return Integer.getInteger("org.apache.activemq.transport.nio.SelectorManager.workQueueCapacity", 0);
      }
  
      private static int getDefaultCorePoolSize() {
          return Integer.getInteger("org.apache.activemq.transport.nio.SelectorManager.corePoolSize", 10);
      }
  
      private static int getDefaultMaximumPoolSize() {
          return Integer.getInteger("org.apache.activemq.transport.nio.SelectorManager.maximumPoolSize", 1024);
      }
  
      private static int getDefaultKeepAliveTime() {
          return Integer.getInteger("org.apache.activemq.transport.nio.SelectorManager.keepAliveTime", 30);
      }
  
      private static int getDefaultMaxChannelsPerWorker() {
          return Integer.getInteger("org.apache.activemq.transport.nio.SelectorManager.maxChannelsPerWorker", 1024);
      }
  
      public static SelectorManager getInstance() {
          return SINGLETON;
      }
  
      public interface Listener {
          void onSelect(SelectorSelection selector);
  
          void onError(SelectorSelection selection, Throwable error);
      }
  
      public synchronized SelectorSelection register(AbstractSelectableChannel selectableChannel, Listener listener) throws IOException {
          SelectorSelection selection = null;
          while (selection == null) {
              if (freeWorkers.size() > 0) {
                  SelectorWorker worker = freeWorkers.getFirst();
                  if (worker.isReleased()) {
                      freeWorkers.remove(worker);
                  } else {
                      worker.retain();
                      selection = new SelectorSelection(worker, selectableChannel, listener);
                  }
              } else {
                  // Worker starts /w retain count of 1
                  SelectorWorker worker = new SelectorWorker(this);
                  freeWorkers.addFirst(worker);
                  selection = new SelectorSelection(worker, selectableChannel, listener);
              }
          }
  
          return selection;
      }
  
      synchronized void onWorkerFullEvent(SelectorWorker worker) {
          freeWorkers.remove(worker);
      }
  
      public synchronized void onWorkerEmptyEvent(SelectorWorker worker) {
          freeWorkers.remove(worker);
      }
  
      public synchronized void onWorkerNotFullEvent(SelectorWorker worker) {
          freeWorkers.addFirst(worker);
      }
  
      public Executor getChannelExecutor() {
          return channelExecutor;
      }
  
      public void setChannelExecutor(Executor channelExecutor) {
          this.channelExecutor = channelExecutor;
      }
  
      public int getMaxChannelsPerWorker() {
          return maxChannelsPerWorker >= 0 ? maxChannelsPerWorker : getDefaultMaxChannelsPerWorker();
      }
  
      public void setMaxChannelsPerWorker(int maxChannelsPerWorker) {
          this.maxChannelsPerWorker = maxChannelsPerWorker;
      }
  
      public Executor getSelectorExecutor() {
          return selectorExecutor;
      }
  
      public void setSelectorExecutor(Executor selectorExecutor) {
          this.selectorExecutor = selectorExecutor;
      }
  }
  