/**
    *
    * 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.executor;
  
  import java.io.IOException;
  import java.io.Writer;
  import java.lang.management.ThreadInfo;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.executor.EventHandler.EventHandlerListener;
  import org.apache.hadoop.hbase.monitoring.ThreadMonitoring;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Maps;
  import com.google.common.util.concurrent.ThreadFactoryBuilder;
  
  /**
   * This is a generic executor service. This component abstracts a
   * threadpool, a queue to which {@link EventType}s can be submitted,
   * and a <code>Runnable</code> that handles the object that is added to the queue.
   *
   * <p>In order to create a new service, create an instance of this class and
   * then do: <code>instance.startExecutorService("myService");</code>.  When done
   * call {@link #shutdown()}.
   *
   * <p>In order to use the service created above, call
   * {@link #submit(EventHandler)}. Register pre- and post- processing listeners
   * by registering your implementation of {@link EventHandler.EventHandlerListener}
   * with {@link #registerListener(EventType, EventHandler.EventHandlerListener)}.  Be sure
   * to deregister your listener when done via {@link #unregisterListener(EventType)}.
   */
  @InterfaceAudience.Private
  public class ExecutorService {
    private static final Log LOG = LogFactory.getLog(ExecutorService.class);
  
    // hold the all the executors created in a map addressable by their names
    private final ConcurrentHashMap<String, Executor> executorMap =
      new ConcurrentHashMap<String, Executor>();
  
    // listeners that are called before and after an event is processed
    private ConcurrentHashMap<EventType, EventHandlerListener> eventHandlerListeners =
      new ConcurrentHashMap<EventType, EventHandlerListener>();
  
    // Name of the server hosting this executor service.
    private final String servername;
  
    /**
     * Default constructor.
     * @param servername Name of the hosting server.
     */
    public ExecutorService(final String servername) {
      super();
      this.servername = servername;
    }
  
    /**
     * Start an executor service with a given name. If there was a service already
     * started with the same name, this throws a RuntimeException.
     * @param name Name of the service to start.
     */
    @VisibleForTesting
    public void startExecutorService(String name, int maxThreads) {
      if (this.executorMap.get(name) != null) {
        throw new RuntimeException("An executor service with the name " + name +
          " is already running!");
      }
      Executor hbes = new Executor(name, maxThreads, this.eventHandlerListeners);
      if (this.executorMap.putIfAbsent(name, hbes) != null) {
        throw new RuntimeException("An executor service with the name " + name +
        " is already running (2)!");
     }
     LOG.debug("Starting executor service name=" + name +
       ", corePoolSize=" + hbes.threadPoolExecutor.getCorePoolSize() +
       ", maxPoolSize=" + hbes.threadPoolExecutor.getMaximumPoolSize());
   }
 
   boolean isExecutorServiceRunning(String name) {
     return this.executorMap.containsKey(name);
   }
 
   public void shutdown() {
     for(Entry<String, Executor> entry: this.executorMap.entrySet()) {
       List<Runnable> wasRunning =
         entry.getValue().threadPoolExecutor.shutdownNow();
       if (!wasRunning.isEmpty()) {
         LOG.info(entry.getValue() + " had " + wasRunning + " on shutdown");
       }
     }
     this.executorMap.clear();
   }
 
   Executor getExecutor(final ExecutorType type) {
     return getExecutor(type.getExecutorName(this.servername));
   }
 
   Executor getExecutor(String name) {
     Executor executor = this.executorMap.get(name);
     return executor;
   }
 
   @VisibleForTesting
   public ThreadPoolExecutor getExecutorThreadPool(final ExecutorType type) {
     return getExecutor(type).getThreadPoolExecutor();
   }
 
   public void startExecutorService(final ExecutorType type, final int maxThreads) {
     String name = type.getExecutorName(this.servername);
     if (isExecutorServiceRunning(name)) {
       LOG.debug("Executor service " + toString() + " already running on " +
         this.servername);
       return;
     }
     startExecutorService(name, maxThreads);
   }
 
   public void submit(final EventHandler eh) {
     Executor executor = getExecutor(eh.getEventType().getExecutorServiceType());
     if (executor == null) {
       // This happens only when events are submitted after shutdown() was
       // called, so dropping them should be "ok" since it means we're
       // shutting down.
       LOG.error("Cannot submit [" + eh + "] because the executor is missing." +
         " Is this process shutting down?");
     } else {
       executor.submit(eh);
     }
   }
 
   /**
    * Subscribe to updates before and after processing instances of
    * {@link EventType}.  Currently only one listener per
    * event type.
    * @param type Type of event we're registering listener for
    * @param listener The listener to run.
    */
   public void registerListener(final EventType type,
       final EventHandlerListener listener) {
     this.eventHandlerListeners.put(type, listener);
   }
 
   /**
    * Stop receiving updates before and after processing instances of
    * {@link EventType}
    * @param type Type of event we're registering listener for
    * @return The listener we removed or null if we did not remove it.
    */
   public EventHandlerListener unregisterListener(final EventType type) {
     return this.eventHandlerListeners.remove(type);
   }
 
   public Map<String, ExecutorStatus> getAllExecutorStatuses() {
     Map<String, ExecutorStatus> ret = Maps.newHashMap();
     for (Map.Entry<String, Executor> e : executorMap.entrySet()) {
       ret.put(e.getKey(), e.getValue().getStatus());
     }
     return ret;
   }
 
   /**
    * Executor instance.
    */
   static class Executor {
     // how long to retain excess threads
     static final long keepAliveTimeInMillis = 1000;
     // the thread pool executor that services the requests
     final TrackingThreadPoolExecutor threadPoolExecutor;
     // work queue to use - unbounded queue
     final BlockingQueue<Runnable> q = new LinkedBlockingQueue<Runnable>();
     private final String name;
     private final Map<EventType, EventHandlerListener> eventHandlerListeners;
     private static final AtomicLong seqids = new AtomicLong(0);
     private final long id;
 
     protected Executor(String name, int maxThreads,
         final Map<EventType, EventHandlerListener> eventHandlerListeners) {
       this.id = seqids.incrementAndGet();
       this.name = name;
       this.eventHandlerListeners = eventHandlerListeners;
       // create the thread pool executor
       this.threadPoolExecutor = new TrackingThreadPoolExecutor(
           maxThreads, maxThreads,
           keepAliveTimeInMillis, TimeUnit.MILLISECONDS, q);
       // name the threads for this threadpool
       ThreadFactoryBuilder tfb = new ThreadFactoryBuilder();
       tfb.setNameFormat(this.name + "-%d");
       this.threadPoolExecutor.setThreadFactory(tfb.build());
     }
 
     /**
      * Submit the event to the queue for handling.
      * @param event
      */
     void submit(final EventHandler event) {
       // If there is a listener for this type, make sure we call the before
       // and after process methods.
       EventHandlerListener listener =
         this.eventHandlerListeners.get(event.getEventType());
       if (listener != null) {
         event.setListener(listener);
       }
       this.threadPoolExecutor.execute(event);
     }
 
     TrackingThreadPoolExecutor getThreadPoolExecutor() {
       return threadPoolExecutor;
     }
 
     @Override
     public String toString() {
       return getClass().getSimpleName() + "-" + id + "-" + name;
     }
 
     public ExecutorStatus getStatus() {
       List<EventHandler> queuedEvents = Lists.newArrayList();
       for (Runnable r : q) {
         if (!(r instanceof EventHandler)) {
           LOG.warn("Non-EventHandler " + r + " queued in " + name);
           continue;
         }
         queuedEvents.add((EventHandler)r);
       }
 
       List<RunningEventStatus> running = Lists.newArrayList();
       for (Map.Entry<Thread, Runnable> e :
           threadPoolExecutor.getRunningTasks().entrySet()) {
         Runnable r = e.getValue();
         if (!(r instanceof EventHandler)) {
           LOG.warn("Non-EventHandler " + r + " running in " + name);
           continue;
         }
         running.add(new RunningEventStatus(e.getKey(), (EventHandler)r));
       }
 
       return new ExecutorStatus(this, queuedEvents, running);
     }
   }
 
   /**
    * A subclass of ThreadPoolExecutor that keeps track of the Runnables that
    * are executing at any given point in time.
    */
   static class TrackingThreadPoolExecutor extends ThreadPoolExecutor {
     private ConcurrentMap<Thread, Runnable> running = Maps.newConcurrentMap();
 
     public TrackingThreadPoolExecutor(int corePoolSize, int maximumPoolSize,
         long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
       super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
     }
 
     @Override
     protected void afterExecute(Runnable r, Throwable t) {
       super.afterExecute(r, t);
       running.remove(Thread.currentThread());
     }
 
     @Override
     protected void beforeExecute(Thread t, Runnable r) {
       Runnable oldPut = running.put(t, r);
       assert oldPut == null : "inconsistency for thread " + t;
       super.beforeExecute(t, r);
     }
 
     /**
      * @return a map of the threads currently running tasks
      * inside this executor. Each key is an active thread,
      * and the value is the task that is currently running.
      * Note that this is not a stable snapshot of the map.
      */
     public ConcurrentMap<Thread, Runnable> getRunningTasks() {
       return running;
     }
   }
 
   /**
    * A snapshot of the status of a particular executor. This includes
    * the contents of the executor's pending queue, as well as the
    * threads and events currently being processed.
    *
    * This is a consistent snapshot that is immutable once constructed.
    */
   public static class ExecutorStatus {
     final Executor executor;
     final List<EventHandler> queuedEvents;
     final List<RunningEventStatus> running;
 
     ExecutorStatus(Executor executor,
         List<EventHandler> queuedEvents,
         List<RunningEventStatus> running) {
       this.executor = executor;
       this.queuedEvents = queuedEvents;
       this.running = running;
     }
 
     /**
      * Dump a textual representation of the executor's status
      * to the given writer.
      *
      * @param out the stream to write to
      * @param indent a string prefix for each line, used for indentation
      */
     public void dumpTo(Writer out, String indent) throws IOException {
       out.write(indent + "Status for executor: " + executor + "\n");
       out.write(indent + "=======================================\n");
       out.write(indent + queuedEvents.size() + " events queued, " +
           running.size() + " running\n");
       if (!queuedEvents.isEmpty()) {
         out.write(indent + "Queued:\n");
         for (EventHandler e : queuedEvents) {
           out.write(indent + "  " + e + "\n");
         }
         out.write("\n");
       }
       if (!running.isEmpty()) {
         out.write(indent + "Running:\n");
         for (RunningEventStatus stat : running) {
           out.write(indent + "  Running on thread '" +
               stat.threadInfo.getThreadName() +
               "': " + stat.event + "\n");
           out.write(ThreadMonitoring.formatThreadInfo(
               stat.threadInfo, indent + "  "));
           out.write("\n");
         }
       }
       out.flush();
     }
   }
 
   /**
    * The status of a particular event that is in the middle of being
    * handled by an executor.
    */
   public static class RunningEventStatus {
     final ThreadInfo threadInfo;
     final EventHandler event;
 
     public RunningEventStatus(Thread t, EventHandler event) {
       this.threadInfo = ThreadMonitoring.getThreadInfo(t);
       this.event = event;
     }
   }
 }