/*
    * Copyright 2009 Red Hat, Inc.
    *
    * Red Hat 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.jboss.netty.handler.execution;
  
  import java.lang.reflect.Method;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.Executor;
  import java.util.concurrent.Executors;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.RejectedExecutionHandler;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelEvent;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelState;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.channel.WriteCompletionEvent;
  import org.jboss.netty.logging.InternalLogger;
  import org.jboss.netty.logging.InternalLoggerFactory;
  import org.jboss.netty.util.DefaultObjectSizeEstimator;
  import org.jboss.netty.util.ObjectSizeEstimator;
  import org.jboss.netty.util.internal.ConcurrentIdentityHashMap;
  import org.jboss.netty.util.internal.LinkedTransferQueue;
  import org.jboss.netty.util.internal.SharedResourceMisuseDetector;
  
  /**
   * A {@link ThreadPoolExecutor} which blocks the task submission when there's
   * too many tasks in the queue.  Both per-{@link Channel} and per-{@link Executor}
   * limitation can be applied.
   * <p>
   * When a task (i.e. {@link Runnable}) is submitted,
   * {@link MemoryAwareThreadPoolExecutor} calls {@link ObjectSizeEstimator#estimateSize(Object)}
   * to get the estimated size of the task in bytes to calculate the amount of
   * memory occupied by the unprocessed tasks.
   * <p>
   * If the total size of the unprocessed tasks exceeds either per-{@link Channel}
   * or per-{@link Executor} threshold, any further {@link #execute(Runnable)}
   * call will block until the tasks in the queue are processed so that the total
   * size goes under the threshold.
   *
   * <h3>Using an alternative task size estimation strategy</h3>
   *
   * Although the default implementation does its best to guess the size of an
   * object of unknown type, it is always good idea to to use an alternative
   * {@link ObjectSizeEstimator} implementation instead of the
   * {@link DefaultObjectSizeEstimator} to avoid incorrect task size calculation,
   * especially when:
   * <ul>
   *   <li>you are using {@link MemoryAwareThreadPoolExecutor} independently from
   *       {@link ExecutionHandler},</li>
   *   <li>you are submitting a task whose type is not {@link ChannelEventRunnable}, or</li>
   *   <li>the message type of the {@link MessageEvent} in the {@link ChannelEventRunnable}
   *       is not {@link ChannelBuffer}.</li>
   * </ul>
   * Here is an example that demonstrates how to implement an {@link ObjectSizeEstimator}
   * which understands a user-defined object:
   * <pre>
   * public class MyRunnable implements {@link Runnable} {
   *
   *     <b>private final byte[] data;</b>
   *
   *     public MyRunnable(byte[] data) {
   *         this.data = data;
   *     }
   *
   *     public void run() {
   *         // Process 'data' ..
   *     }
   * }
   *
   * public class MyObjectSizeEstimator extends {@link DefaultObjectSizeEstimator} {
   *
   *     {@literal @Override}
   *     public int estimateSize(Object o) {
   *         if (<b>o instanceof MyRunnable</b>) {
   *             <b>return ((MyRunnable) o).data.length + 8;</b>
   *         }
   *         return super.estimateSize(o);
   *     }
   * }
  *
  * {@link ThreadPoolExecutor} pool = new {@link MemoryAwareThreadPoolExecutor}(
  *         16, 65536, 1048576, 30, {@link TimeUnit}.SECONDS,
  *         <b>new MyObjectSizeEstimator()</b>,
  *         {@link Executors}.defaultThreadFactory());
  *
  * <b>pool.execute(new MyRunnable(data));</b>
  * </pre>
  *
  * <h3>Event execution order</h3>
  *
  * Please note that this executor does not maintain the order of the
  * {@link ChannelEvent}s for the same {@link Channel}.  For example,
  * you can even receive a {@code "channelClosed"} event before a
  * {@code "messageReceived"} event, as depicted by the following diagram.
  *
  * For example, the events can be processed as depicted below:
  *
  * <pre>
  *           --------------------------------&gt; Timeline --------------------------------&gt;
  *
  * Thread X: --- Channel A (Event 2) --- Channel A (Event 1) ---------------------------&gt;
  *
  * Thread Y: --- Channel A (Event 3) --- Channel B (Event 2) --- Channel B (Event 3) ---&gt;
  *
  * Thread Z: --- Channel B (Event 1) --- Channel B (Event 4) --- Channel A (Event 4) ---&gt;
  * </pre>
  *
  * To maintain the event order, you must use {@link OrderedMemoryAwareThreadPoolExecutor}.
  *
  * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
  * @author <a href="http://gleamynode.net/">Trustin Lee</a>
  *
  * @version $Rev: 2351 $, $Date: 2010-08-26 11:55:10 +0900 (Thu, 26 Aug 2010) $
  *
  * @apiviz.has org.jboss.netty.util.ObjectSizeEstimator oneway - -
  * @apiviz.has org.jboss.netty.handler.execution.ChannelEventRunnable oneway - - executes
  */
 public class MemoryAwareThreadPoolExecutor extends ThreadPoolExecutor {
 
     private static final InternalLogger logger =
         InternalLoggerFactory.getInstance(MemoryAwareThreadPoolExecutor.class);
 
     private static final SharedResourceMisuseDetector misuseDetector =
         new SharedResourceMisuseDetector(MemoryAwareThreadPoolExecutor.class);
 
     private volatile Settings settings;
 
     private final ConcurrentMap<Channel, AtomicLong> channelCounters =
         new ConcurrentIdentityHashMap<Channel, AtomicLong>();
     private final Limiter totalLimiter;
 
     /**
      * Creates a new instance.
      *
      * @param corePoolSize          the maximum number of active threads
      * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
      *                              Specify {@code 0} to disable.
      * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
      *                              Specify {@code 0} to disable.
      */
     public MemoryAwareThreadPoolExecutor(
             int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize) {
 
         this(corePoolSize, maxChannelMemorySize, maxTotalMemorySize, 30, TimeUnit.SECONDS);
     }
 
     /**
      * Creates a new instance.
      *
      * @param corePoolSize          the maximum number of active threads
      * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
      *                              Specify {@code 0} to disable.
      * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
      *                              Specify {@code 0} to disable.
      * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
      * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
      */
     public MemoryAwareThreadPoolExecutor(
             int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
             long keepAliveTime, TimeUnit unit) {
 
         this(corePoolSize, maxChannelMemorySize, maxTotalMemorySize, keepAliveTime, unit, Executors.defaultThreadFactory());
     }
 
     /**
      * Creates a new instance.
      *
      * @param corePoolSize          the maximum number of active threads
      * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
      *                              Specify {@code 0} to disable.
      * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
      *                              Specify {@code 0} to disable.
      * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
      * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
      * @param threadFactory         the {@link ThreadFactory} of this pool
      */
     public MemoryAwareThreadPoolExecutor(
             int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
             long keepAliveTime, TimeUnit unit, ThreadFactory threadFactory) {
 
         this(corePoolSize, maxChannelMemorySize, maxTotalMemorySize, keepAliveTime, unit, new DefaultObjectSizeEstimator(), threadFactory);
     }
 
     /**
      * Creates a new instance.
      *
      * @param corePoolSize          the maximum number of active threads
      * @param maxChannelMemorySize  the maximum total size of the queued events per channel.
      *                              Specify {@code 0} to disable.
      * @param maxTotalMemorySize    the maximum total size of the queued events for this pool
      *                              Specify {@code 0} to disable.
      * @param keepAliveTime         the amount of time for an inactive thread to shut itself down
      * @param unit                  the {@link TimeUnit} of {@code keepAliveTime}
      * @param threadFactory         the {@link ThreadFactory} of this pool
      * @param objectSizeEstimator   the {@link ObjectSizeEstimator} of this pool
      */
     public MemoryAwareThreadPoolExecutor(
             int corePoolSize, long maxChannelMemorySize, long maxTotalMemorySize,
             long keepAliveTime, TimeUnit unit, ObjectSizeEstimator objectSizeEstimator,
             ThreadFactory threadFactory) {
 
         super(corePoolSize, corePoolSize, keepAliveTime, unit,
               new LinkedTransferQueue<Runnable>(), threadFactory, new NewThreadRunsPolicy());
 
         if (objectSizeEstimator == null) {
             throw new NullPointerException("objectSizeEstimator");
         }
         if (maxChannelMemorySize < 0) {
             throw new IllegalArgumentException(
                     "maxChannelMemorySize: " + maxChannelMemorySize);
         }
         if (maxTotalMemorySize < 0) {
             throw new IllegalArgumentException(
                     "maxTotalMemorySize: " + maxTotalMemorySize);
         }
 
         // Call allowCoreThreadTimeOut(true) using reflection
         // because it is not supported in Java 5.
         try {
             Method m = getClass().getMethod("allowCoreThreadTimeOut", new Class[] { boolean.class });
             m.invoke(this, Boolean.TRUE);
         } catch (Throwable t) {
             // Java 5
             logger.debug(
                     "ThreadPoolExecutor.allowCoreThreadTimeOut() is not " +
                     "supported in this platform.");
         }
 
         settings = new Settings(
                 objectSizeEstimator, maxChannelMemorySize);
 
         if (maxTotalMemorySize == 0) {
             totalLimiter = null;
         } else {
             totalLimiter = new Limiter(maxTotalMemorySize);
         }
 
         // Misuse check
         misuseDetector.increase();
     }
 
     @Override
     protected void terminated() {
         super.terminated();
         misuseDetector.decrease();
     }
 
     /**
      * Returns the {@link ObjectSizeEstimator} of this pool.
      */
     public ObjectSizeEstimator getObjectSizeEstimator() {
         return settings.objectSizeEstimator;
     }
 
     /**
      * Sets the {@link ObjectSizeEstimator} of this pool.
      */
     public void setObjectSizeEstimator(ObjectSizeEstimator objectSizeEstimator) {
         if (objectSizeEstimator == null) {
             throw new NullPointerException("objectSizeEstimator");
         }
 
         settings = new Settings(
                 objectSizeEstimator,
                 settings.maxChannelMemorySize);
     }
 
     /**
      * Returns the maximum total size of the queued events per channel.
      */
     public long getMaxChannelMemorySize() {
         return settings.maxChannelMemorySize;
     }
 
     /**
      * Sets the maximum total size of the queued events per channel.
      * Specify {@code 0} to disable.
      */
     public void setMaxChannelMemorySize(long maxChannelMemorySize) {
         if (maxChannelMemorySize < 0) {
             throw new IllegalArgumentException(
                     "maxChannelMemorySize: " + maxChannelMemorySize);
         }
 
         if (getTaskCount() > 0) {
             throw new IllegalStateException(
                     "can't be changed after a task is executed");
         }
 
         settings = new Settings(
                 settings.objectSizeEstimator,
                 maxChannelMemorySize);
     }
 
     /**
      * Returns the maximum total size of the queued events for this pool.
      */
     public long getMaxTotalMemorySize() {
         return totalLimiter.limit;
     }
 
     /**
      * @deprecated <tt>maxTotalMemorySize</tt> is not modifiable anymore.
      */
     @Deprecated
     public void setMaxTotalMemorySize(long maxTotalMemorySize) {
         if (maxTotalMemorySize < 0) {
             throw new IllegalArgumentException(
                     "maxTotalMemorySize: " + maxTotalMemorySize);
         }
 
         if (getTaskCount() > 0) {
             throw new IllegalStateException(
                     "can't be changed after a task is executed");
         }
     }
 
     @Override
     public void execute(Runnable command) {
         if (!(command instanceof ChannelEventRunnable)) {
             command = new MemoryAwareRunnable(command);
         }
 
         increaseCounter(command);
         doExecute(command);
     }
 
     /**
      * Put the actual execution logic here.  The default implementation simply
      * calls {@link #doUnorderedExecute(Runnable)}.
      */
     protected void doExecute(Runnable task) {
         doUnorderedExecute(task);
     }
 
     /**
      * Executes the specified task without maintaining the event order.
      */
     protected final void doUnorderedExecute(Runnable task) {
         super.execute(task);
     }
 
     @Override
     public boolean remove(Runnable task) {
         boolean removed = super.remove(task);
         if (removed) {
             decreaseCounter(task);
         }
         return removed;
     }
 
     @Override
     protected void beforeExecute(Thread t, Runnable r) {
         super.beforeExecute(t, r);
         decreaseCounter(r);
     }
 
     protected void increaseCounter(Runnable task) {
         if (!shouldCount(task)) {
             return;
         }
 
         Settings settings = this.settings;
         long maxChannelMemorySize = settings.maxChannelMemorySize;
 
         int increment = settings.objectSizeEstimator.estimateSize(task);
 
         if (task instanceof ChannelEventRunnable) {
             ChannelEventRunnable eventTask = (ChannelEventRunnable) task;
             eventTask.estimatedSize = increment;
             Channel channel = eventTask.getEvent().getChannel();
             long channelCounter = getChannelCounter(channel).addAndGet(increment);
             //System.out.println("IC: " + channelCounter + ", " + increment);
             if (maxChannelMemorySize != 0 && channelCounter >= maxChannelMemorySize && channel.isOpen()) {
                 if (channel.isReadable()) {
                     //System.out.println("UNREADABLE");
                     ChannelHandlerContext ctx = eventTask.getContext();
                     if (ctx.getHandler() instanceof ExecutionHandler) {
                         // readSuspended = true;
                         ctx.setAttachment(Boolean.TRUE);
                     }
                     channel.setReadable(false);
                 }
             }
         } else {
             ((MemoryAwareRunnable) task).estimatedSize = increment;
         }
 
         if (totalLimiter != null) {
             totalLimiter.increase(increment);
         }
     }
 
     protected void decreaseCounter(Runnable task) {
         if (!shouldCount(task)) {
             return;
         }
 
         Settings settings = this.settings;
         long maxChannelMemorySize = settings.maxChannelMemorySize;
 
         int increment;
         if (task instanceof ChannelEventRunnable) {
             increment = ((ChannelEventRunnable) task).estimatedSize;
         } else {
             increment = ((MemoryAwareRunnable) task).estimatedSize;
         }
 
         if (totalLimiter != null) {
             totalLimiter.decrease(increment);
         }
 
         if (task instanceof ChannelEventRunnable) {
             ChannelEventRunnable eventTask = (ChannelEventRunnable) task;
             Channel channel = eventTask.getEvent().getChannel();
             long channelCounter = getChannelCounter(channel).addAndGet(-increment);
             //System.out.println("DC: " + channelCounter + ", " + increment);
             if (maxChannelMemorySize != 0 && channelCounter < maxChannelMemorySize && channel.isOpen()) {
                 if (!channel.isReadable()) {
                     //System.out.println("READABLE");
                     ChannelHandlerContext ctx = eventTask.getContext();
                     if (ctx.getHandler() instanceof ExecutionHandler) {
                         // readSuspended = false;
                         ctx.setAttachment(null);
                     }
                     channel.setReadable(true);
                 }
             }
         }
     }
 
     private AtomicLong getChannelCounter(Channel channel) {
         AtomicLong counter = channelCounters.get(channel);
         if (counter == null) {
             counter = new AtomicLong();
             AtomicLong oldCounter = channelCounters.putIfAbsent(channel, counter);
             if (oldCounter != null) {
                 counter = oldCounter;
             }
         }
 
         // Remove the entry when the channel closes.
         if (!channel.isOpen()) {
             channelCounters.remove(channel);
         }
         return counter;
     }
 
     /**
      * Returns {@code true} if and only if the specified {@code task} should
      * be counted to limit the global and per-channel memory consumption.
      * To override this method, you must call {@code super.shouldCount()} to
      * make sure important tasks are not counted.
      */
     protected boolean shouldCount(Runnable task) {
         if (task instanceof ChannelEventRunnable) {
             ChannelEventRunnable r = (ChannelEventRunnable) task;
             ChannelEvent e = r.getEvent();
             if (e instanceof WriteCompletionEvent) {
                 return false;
             } else if (e instanceof ChannelStateEvent) {
                 if (((ChannelStateEvent) e).getState() == ChannelState.INTEREST_OPS) {
                     return false;
                 }
             }
         }
         return true;
     }
 
     private static final class Settings {
         final ObjectSizeEstimator objectSizeEstimator;
         final long maxChannelMemorySize;
 
         Settings(ObjectSizeEstimator objectSizeEstimator,
                  long maxChannelMemorySize) {
             this.objectSizeEstimator = objectSizeEstimator;
             this.maxChannelMemorySize = maxChannelMemorySize;
         }
     }
 
     private static final class NewThreadRunsPolicy implements RejectedExecutionHandler {
         NewThreadRunsPolicy() {
             super();
         }
 
         public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
             try {
                 final Thread t = new Thread(r, "Temporary task executor");
                 t.start();
             } catch (Throwable e) {
                 throw new RejectedExecutionException(
                         "Failed to start a new thread", e);
             }
         }
     }
 
     private static final class MemoryAwareRunnable implements Runnable {
         final Runnable task;
         int estimatedSize;
 
         MemoryAwareRunnable(Runnable task) {
             this.task = task;
         }
 
         public void run() {
             task.run();
         }
     }
 
 
     private static class Limiter {
 
         final long limit;
         private long counter;
         private int waiters;
 
         Limiter(long limit) {
             super();
             this.limit = limit;
         }
 
         synchronized void increase(long amount) {
             while (counter >= limit) {
                 waiters ++;
                 try {
                     wait();
                 } catch (InterruptedException e) {
                     // Ignore
                 } finally {
                     waiters --;
                 }
             }
             counter += amount;
         }
 
         synchronized void decrease(long amount) {
             counter -= amount;
             if (counter < limit && waiters > 0) {
                 notifyAll();
             }
         }
     }
 }