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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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.buffer;
  
  import java.lang.ref.ReferenceQueue;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  /**
   * A {@link ChannelBufferFactory} which pre-allocates a large chunk of direct
   * buffer and returns its slice on demand.  Direct buffers are reclaimed via
   * {@link ReferenceQueue} in most JDK implementations, and therefore they are
   * deallocated less efficiently than an ordinary heap buffer.  Consequently,
   * a user will get {@link OutOfMemoryError} when one tries to allocate small
   * direct buffers more often than the GC throughput of direct buffers, which
   * is much lower than the GC throughput of heap buffers.  This factory avoids
   * this problem by allocating a large chunk of pre-allocated direct buffer and
   * reducing the number of the garbage collected internal direct buffer objects.
   */
  public class DirectChannelBufferFactory extends AbstractChannelBufferFactory {
  
      private static final DirectChannelBufferFactory INSTANCE_BE =
          new DirectChannelBufferFactory(ByteOrder.BIG_ENDIAN);
  
      private static final DirectChannelBufferFactory INSTANCE_LE =
          new DirectChannelBufferFactory(ByteOrder.LITTLE_ENDIAN);
  
      public static ChannelBufferFactory getInstance() {
          return INSTANCE_BE;
      }
  
      public static ChannelBufferFactory getInstance(ByteOrder defaultEndianness) {
          if (defaultEndianness == ByteOrder.BIG_ENDIAN) {
              return INSTANCE_BE;
          } else if (defaultEndianness == ByteOrder.LITTLE_ENDIAN) {
              return INSTANCE_LE;
          } else if (defaultEndianness == null) {
              throw new NullPointerException("defaultEndianness");
          } else {
              throw new IllegalStateException("Should not reach here");
          }
      }
  
      private final Object bigEndianLock = new Object();
      private final Object littleEndianLock = new Object();
      private final int preallocatedBufCapacity;
      private ChannelBuffer preallocatedBEBuf;
      private int preallocatedBEBufPos;
      private ChannelBuffer preallocatedLEBuf;
      private int preallocatedLEBufPos;
  
      /**
       * Creates a new factory whose default {@link ByteOrder} is
       * {@link ByteOrder#BIG_ENDIAN}.
       */
      public DirectChannelBufferFactory() {
          this(ByteOrder.BIG_ENDIAN);
      }
  
      /**
       * Creates a new factory whose default {@link ByteOrder} is
       * {@link ByteOrder#BIG_ENDIAN}.
       */
      public DirectChannelBufferFactory(int preallocatedBufferCapacity) {
          this(ByteOrder.BIG_ENDIAN, preallocatedBufferCapacity);
      }
  
      /**
       * Creates a new factory with the specified default {@link ByteOrder}.
       *
       * @param defaultOrder the default {@link ByteOrder} of this factory
       */
      public DirectChannelBufferFactory(ByteOrder defaultOrder) {
          this(defaultOrder, 1048576);
      }
  
      /**
       * Creates a new factory with the specified default {@link ByteOrder}.
       *
       * @param defaultOrder the default {@link ByteOrder} of this factory
       */
      public DirectChannelBufferFactory(ByteOrder defaultOrder, int preallocatedBufferCapacity) {
          super(defaultOrder);
          if (preallocatedBufferCapacity <= 0) {
              throw new IllegalArgumentException(
                      "preallocatedBufCapacity must be greater than 0: " + preallocatedBufferCapacity);
         }
 
         preallocatedBufCapacity = preallocatedBufferCapacity;
     }
 
     public ChannelBuffer getBuffer(ByteOrder order, int capacity) {
         if (order == null) {
             throw new NullPointerException("order");
         }
         if (capacity < 0) {
             throw new IllegalArgumentException("capacity: " + capacity);
         }
         if (capacity == 0) {
             return ChannelBuffers.EMPTY_BUFFER;
         }
         if (capacity >= preallocatedBufCapacity) {
             return ChannelBuffers.directBuffer(order, capacity);
         }
 
         ChannelBuffer slice;
         if (order == ByteOrder.BIG_ENDIAN) {
             slice = allocateBigEndianBuffer(capacity);
         } else {
             slice = allocateLittleEndianBuffer(capacity);
         }
         slice.clear();
         return slice;
     }
 
     public ChannelBuffer getBuffer(ByteOrder order, byte[] array, int offset, int length) {
         if (array == null) {
             throw new NullPointerException("array");
         }
         if (offset < 0) {
             throw new IndexOutOfBoundsException("offset: " + offset);
         }
         if (length == 0) {
             return ChannelBuffers.EMPTY_BUFFER;
         }
         if (offset + length > array.length) {
             throw new IndexOutOfBoundsException("length: " + length);
         }
 
         ChannelBuffer buf = getBuffer(order, length);
         buf.writeBytes(array, offset, length);
         return buf;
     }
 
     public ChannelBuffer getBuffer(ByteBuffer nioBuffer) {
         if (!nioBuffer.isReadOnly() && nioBuffer.isDirect()) {
             return ChannelBuffers.wrappedBuffer(nioBuffer);
         }
 
         ChannelBuffer buf = getBuffer(nioBuffer.order(), nioBuffer.remaining());
         int pos = nioBuffer.position();
         buf.writeBytes(nioBuffer);
         nioBuffer.position(pos);
         return buf;
     }
 
     private ChannelBuffer allocateBigEndianBuffer(int capacity) {
         ChannelBuffer slice;
         synchronized (bigEndianLock) {
             if (preallocatedBEBuf == null) {
                 preallocatedBEBuf = ChannelBuffers.directBuffer(ByteOrder.BIG_ENDIAN, preallocatedBufCapacity);
                 slice = preallocatedBEBuf.slice(0, capacity);
                 preallocatedBEBufPos = capacity;
             } else if (preallocatedBEBuf.capacity() - preallocatedBEBufPos >= capacity) {
                 slice = preallocatedBEBuf.slice(preallocatedBEBufPos, capacity);
                 preallocatedBEBufPos += capacity;
             } else {
                 preallocatedBEBuf = ChannelBuffers.directBuffer(ByteOrder.BIG_ENDIAN, preallocatedBufCapacity);
                 slice = preallocatedBEBuf.slice(0, capacity);
                 preallocatedBEBufPos = capacity;
             }
         }
         return slice;
     }
 
     private ChannelBuffer allocateLittleEndianBuffer(int capacity) {
         ChannelBuffer slice;
         synchronized (littleEndianLock) {
             if (preallocatedLEBuf == null) {
                 preallocatedLEBuf = ChannelBuffers.directBuffer(ByteOrder.LITTLE_ENDIAN, preallocatedBufCapacity);
                 slice = preallocatedLEBuf.slice(0, capacity);
                 preallocatedLEBufPos = capacity;
             } else if (preallocatedLEBuf.capacity() - preallocatedLEBufPos >= capacity) {
                 slice = preallocatedLEBuf.slice(preallocatedLEBufPos, capacity);
                 preallocatedLEBufPos += capacity;
             } else {
                 preallocatedLEBuf = ChannelBuffers.directBuffer(ByteOrder.LITTLE_ENDIAN, preallocatedBufCapacity);
                 slice = preallocatedLEBuf.slice(0, capacity);
                 preallocatedLEBufPos = capacity;
             }
         }
         return slice;
     }
 }