content: /*
   * 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.cassandra.io.util;
  
  import java.nio.ByteBuffer;
  import java.util.EnumMap;
  
  import io.netty.util.concurrent.FastThreadLocal;
  
  import org.apache.cassandra.io.compress.BufferType;
  import org.apache.cassandra.utils.memory.MemoryUtil;
  
  /**
   * Utility class that allow buffers to be reused by storing them in a thread local instance.
   */
  public final class ThreadLocalByteBufferHolder
  {
      private static final EnumMap<BufferType, FastThreadLocal<ByteBuffer>> reusableBBHolder = new EnumMap<>(BufferType.class);
      // Convenience variable holding a ref to the current resuableBB to avoid map lookups
      private final FastThreadLocal<ByteBuffer> reusableBB;
  
      static
      {
          for (BufferType bbType : BufferType.values())
          {
              reusableBBHolder.put(bbType, new FastThreadLocal<ByteBuffer>()
              {
                  protected ByteBuffer initialValue()
                  {
                      return ByteBuffer.allocate(0);
                  }
              });
          }
      };
  
      /**
       * The type of buffer that will be returned
       */
      private final BufferType bufferType;
  
      public ThreadLocalByteBufferHolder(BufferType bufferType)
      {
          this.bufferType = bufferType;
          this.reusableBB = reusableBBHolder.get(bufferType);
      }
  
      /**
       * Returns the buffer for the current thread.
       *
       * <p>If the buffer for the current thread does not have a capacity large enough. A new buffer with the requested
       *  size will be instatiated an will replace the existing one.</p>
       *
       * @param size the buffer size
       * @return the buffer for the current thread.
       */
      public ByteBuffer getBuffer(int size)
      {
          ByteBuffer buffer = reusableBB.get();
          if (buffer.capacity() < size)
          {
              MemoryUtil.clean(buffer);
              buffer = bufferType.allocate(size);
              reusableBB.set(buffer);
          }
          buffer.clear().limit(size);
          return buffer;
      }
  }
  