/*
    *  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.mina.core.buffer;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Queue;
  
  import org.apache.mina.util.CircularQueue;
  
  /**
   * An {@link IoBufferAllocator} that caches the buffers which are likely to
   * be reused during auto-expansion of the buffers.
   * <p>
   * In {@link SimpleBufferAllocator}, the underlying {@link ByteBuffer} of
   * the {@link IoBuffer} is reallocated on its capacity change, which means
   * the newly allocated bigger {@link ByteBuffer} replaces the old small
   * {@link ByteBuffer}.  Consequently, the old {@link ByteBuffer} is marked
   * for garbage collection.
   * <p>
   * It's not a problem in most cases as long as the capacity change doesn't
   * happen frequently.  However, once it happens too often, it burdens the
   * VM and the cost of filling the newly allocated {@link ByteBuffer} with
   * {@code NUL} surpass the cost of accessing the cache.  In 2 dual-core
   * Opteron Italy 270 processors, {@link CachedBufferAllocator} outperformed
   * {@link SimpleBufferAllocator} in the following situation:
   * <ul>
   * <li>when a 32 bytes buffer is expanded 4 or more times,</li> 
   * <li>when a 64 bytes buffer is expanded 4 or more times,</li>
   * <li>when a 128 bytes buffer is expanded 2 or more times,</li>
   * <li>and when a 256 bytes or bigger buffer is expanded 1 or more times.</li>
   * </ul>
   * Please note the observation above is subject to change in a different
   * environment.
   * <p>
   * {@link CachedBufferAllocator} uses {@link ThreadLocal} to store the cached
   * buffer, allocates buffers whose capacity is power of 2 only and provides
   * performance advantage if {@link IoBuffer#free()} is called properly.
   *
   * @author The Apache MINA Project (dev@mina.apache.org)
   */
  public class CachedBufferAllocator implements IoBufferAllocator {
  
      private static final int DEFAULT_MAX_POOL_SIZE = 8;
      private static final int DEFAULT_MAX_CACHED_BUFFER_SIZE = 1 << 18; // 256KB
      
      private final int maxPoolSize;
      private final int maxCachedBufferSize;
  
      private final ThreadLocal<Map<Integer, Queue<CachedBuffer>>> heapBuffers;
      private final ThreadLocal<Map<Integer, Queue<CachedBuffer>>> directBuffers;
      
      /**
       * Creates a new instance with the default parameters
       * ({@literal #DEFAULT_MAX_POOL_SIZE} and {@literal #DEFAULT_MAX_CACHED_BUFFER_SIZE}). 
       */
      public CachedBufferAllocator() {
          this(DEFAULT_MAX_POOL_SIZE, DEFAULT_MAX_CACHED_BUFFER_SIZE);
      }
      
      /**
       * Creates a new instance.
       * 
       * @param maxPoolSize the maximum number of buffers with the same capacity per thread.
       *                    <tt>0</tt> disables this limitation.
       * @param maxCachedBufferSize the maximum capacity of a cached buffer.
       *                            A buffer whose capacity is bigger than this value is
       *                            not pooled. <tt>0</tt> disables this limitation.
       */
      public CachedBufferAllocator(int maxPoolSize, int maxCachedBufferSize) {
          if (maxPoolSize < 0) {
              throw new IllegalArgumentException("maxPoolSize: " + maxPoolSize);
          }
          if (maxCachedBufferSize < 0) {
              throw new IllegalArgumentException("maxCachedBufferSize: " + maxCachedBufferSize);
          }
          
          this.maxPoolSize = maxPoolSize;
          this.maxCachedBufferSize = maxCachedBufferSize;
          
         this.heapBuffers = new ThreadLocal<Map<Integer, Queue<CachedBuffer>>>() {
             @Override
             protected Map<Integer, Queue<CachedBuffer>> initialValue() {
                 return newPoolMap();
             }
         };
         this.directBuffers = new ThreadLocal<Map<Integer, Queue<CachedBuffer>>>() {
             @Override
             protected Map<Integer, Queue<CachedBuffer>> initialValue() {
                 return newPoolMap();
             }
         };
     }
     
     /**
      * Returns the maximum number of buffers with the same capacity per thread.
      * <tt>0</tt> means 'no limitation'.
      */
     public int getMaxPoolSize() {
         return maxPoolSize;
     }
 
     /**
      * Returns the maximum capacity of a cached buffer.  A buffer whose
      * capacity is bigger than this value is not pooled.  <tt>0</tt> means
      * 'no limitation'.
      */
     public int getMaxCachedBufferSize() {
         return maxCachedBufferSize;
     }
 
     Map<Integer, Queue<CachedBuffer>> newPoolMap() {
         Map<Integer, Queue<CachedBuffer>> poolMap =
             new HashMap<Integer, Queue<CachedBuffer>>();
         int poolSize = maxPoolSize == 0? DEFAULT_MAX_POOL_SIZE : maxPoolSize;
         for (int i = 0; i < 31; i ++) {
             poolMap.put(1 << i, new CircularQueue<CachedBuffer>(poolSize));
         }
         poolMap.put(0, new CircularQueue<CachedBuffer>(poolSize));
         poolMap.put(Integer.MAX_VALUE, new CircularQueue<CachedBuffer>(poolSize));
         return poolMap;
     }
 
     public IoBuffer allocate(int requestedCapacity, boolean direct) {
         int actualCapacity = IoBuffer.normalizeCapacity(requestedCapacity);
         IoBuffer buf ;
         if (maxCachedBufferSize != 0 && actualCapacity > maxCachedBufferSize) {
             if (direct) {
                 buf = wrap(ByteBuffer.allocateDirect(actualCapacity));
             } else {
                 buf = wrap(ByteBuffer.allocate(actualCapacity));
             }
         } else {
             Queue<CachedBuffer> pool;
             if (direct) {
                 pool = directBuffers.get().get(actualCapacity);
             } else {
                 pool = heapBuffers.get().get(actualCapacity);
             }
             
             // Recycle if possible.
             buf = pool.poll();
             if (buf != null) {
                 buf.clear();
                 buf.setAutoExpand(false);
                 buf.order(ByteOrder.BIG_ENDIAN);
             } else {
                 if (direct) {
                     buf = wrap(ByteBuffer.allocateDirect(actualCapacity));
                 } else {
                     buf = wrap(ByteBuffer.allocate(actualCapacity));
                 }
             }
         }
         
         buf.limit(requestedCapacity);
         return buf;
     }
     
     public ByteBuffer allocateNioBuffer(int capacity, boolean direct) {
         return allocate(capacity, direct).buf();
     }
     
     public IoBuffer wrap(ByteBuffer nioBuffer) {
         return new CachedBuffer(nioBuffer);
     }
 
     public void dispose() {
         // Do nothing
     }
     
     private class CachedBuffer extends AbstractIoBuffer {
         private final Thread ownerThread;
         private ByteBuffer buf;
 
         protected CachedBuffer(ByteBuffer buf) {
             super(CachedBufferAllocator.this, buf.capacity());
             this.ownerThread = Thread.currentThread();
             this.buf = buf;
             buf.order(ByteOrder.BIG_ENDIAN);
         }
         
         protected CachedBuffer(CachedBuffer parent, ByteBuffer buf) {
             super(parent);
             this.ownerThread = Thread.currentThread();
             this.buf = buf;
         }
 
         @Override
         public ByteBuffer buf() {
             if (buf == null) {
                 throw new IllegalStateException("Buffer has been freed already.");
             }
             return buf;
         }
         
         @Override
         protected void buf(ByteBuffer buf) {
             ByteBuffer oldBuf = this.buf;
             this.buf = buf;
             free(oldBuf);
         }
 
         @Override
         protected IoBuffer duplicate0() {
             return new CachedBuffer(this, buf().duplicate());
         }
 
         @Override
         protected IoBuffer slice0() {
             return new CachedBuffer(this, buf().slice());
         }
 
         @Override
         protected IoBuffer asReadOnlyBuffer0() {
             return new CachedBuffer(this, buf().asReadOnlyBuffer());
         }
 
         @Override
         public byte[] array() {
             return buf().array();
         }
 
         @Override
         public int arrayOffset() {
             return buf().arrayOffset();
         }
 
         @Override
         public boolean hasArray() {
             return buf().hasArray();
         }
 
         @Override
         public void free() {
             free(buf);
             buf = null;
         }
         
         private void free(ByteBuffer oldBuf) {
             if (oldBuf == null || oldBuf.capacity() > maxCachedBufferSize ||
                 oldBuf.isReadOnly() || isDerived() ||
                 Thread.currentThread() != ownerThread) {
                 return;
             }
 
             // Add to the cache.
             Queue<CachedBuffer> pool;
             if (oldBuf.isDirect()) {
                 pool = directBuffers.get().get(oldBuf.capacity());
             } else {
                 pool = heapBuffers.get().get(oldBuf.capacity());
             }
             
             if (pool == null) {
                 return;
             }
 
             // Restrict the size of the pool to prevent OOM.
             if (maxPoolSize == 0 || pool.size() < maxPoolSize) {
                 pool.offer(new CachedBuffer(oldBuf));
             }
         }
     }
 }