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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.channel.socket.nio;
  
  import org.jboss.netty.util.ExternalResourceReleasable;
  import org.jboss.netty.util.internal.ByteBufferUtil;
  
  import java.nio.ByteBuffer;
  
  final class SocketReceiveBufferAllocator implements ExternalResourceReleasable {
  
      private ByteBuffer buf;
      private int exceedCount;
      private final int maxExceedCount;
      private final int percentual;
  
      SocketReceiveBufferAllocator() {
          this(16, 80);
      }
  
      SocketReceiveBufferAllocator(int maxExceedCount, int percentual) {
          this.maxExceedCount = maxExceedCount;
          this.percentual = percentual;
      }
  
      ByteBuffer get(int size) {
          if (buf == null) {
              return newBuffer(size);
          }
          if (buf.capacity() < size) {
              return newBuffer(size);
          }
          if (buf.capacity() * percentual / 100 > size) {
              if (++exceedCount == maxExceedCount) {
                 return newBuffer(size);
              } else {
                  buf.clear();
              }
          } else {
              exceedCount = 0;
              buf.clear();
          }
          return buf;
      }
  
      private ByteBuffer newBuffer(int size) {
          if (buf != null) {
              exceedCount = 0;
              ByteBufferUtil.destroy(buf);
          }
          buf = ByteBuffer.allocateDirect(normalizeCapacity(size));
          return buf;
      }
  
      private static int normalizeCapacity(int capacity) {
          // Normalize to multiple of 1024
          int q = capacity >>> 10;
          int r = capacity & 1023;
          if (r != 0) {
              q ++;
          }
          return q << 10;
      }
  
      public void releaseExternalResources() {
          if (buf != null) {
              ByteBufferUtil.destroy(buf);
          }
      }
  }