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.Queue;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.cassandra.io.compress.BufferType;
  import org.apache.cassandra.utils.memory.MemoryUtil;
  import org.jctools.queues.MpmcArrayQueue;
  
  /**
   * A very simple Bytebuffer pool with a fixed allocation size and a cached max allocation count. Will allow
   * you to go past the "max", freeing all buffers allocated beyond the max buffer count on release.
   *
   * Has a reusable thread local ByteBuffer that users can make use of.
   */
  public class SimpleCachedBufferPool
  {
      private final ThreadLocalByteBufferHolder bufferHolder;
  
      private final Queue<ByteBuffer> bufferPool;
  
      /**
       * The number of buffers currently used.
       */
      private AtomicInteger usedBuffers = new AtomicInteger(0);
  
      /**
       * Maximum number of buffers in the compression pool. Any buffers above this count that are allocated will be cleaned
       * upon release rather than held and re-used.
       */
      private final int maxBufferPoolSize;
  
      /**
       * Size of individual buffer segments on allocation.
       */
      private final int bufferSize;
  
      private final BufferType preferredReusableBufferType;
  
      public SimpleCachedBufferPool(int maxBufferPoolSize, int bufferSize, BufferType preferredReusableBufferType)
      {
          // We want to use a bounded queue to ensure that we do not pool more buffers than maxBufferPoolSize
          this.bufferPool = new MpmcArrayQueue<>(maxBufferPoolSize);
          this.maxBufferPoolSize = maxBufferPoolSize;
          this.bufferSize = bufferSize;
          this.preferredReusableBufferType = preferredReusableBufferType;
          this.bufferHolder = new ThreadLocalByteBufferHolder(preferredReusableBufferType);
      }
  
      public ByteBuffer createBuffer()
      {
          usedBuffers.incrementAndGet();
          ByteBuffer buf = bufferPool.poll();
          if (buf != null)
          {
              buf.clear();
              return buf;
          }
          return preferredReusableBufferType.allocate(bufferSize);
      }
  
      public ByteBuffer getThreadLocalReusableBuffer(int size)
      {
          return bufferHolder.getBuffer(size);
      }
  
      public void releaseBuffer(ByteBuffer buffer)
      {
          assert buffer != null;
          assert preferredReusableBufferType == BufferType.typeOf(buffer);
  
          usedBuffers.decrementAndGet();
  
          // We use a bounded queue. By consequence if we have reached the maximum size for the buffer pool
          // offer will return false and we know that we can simply get rid of the buffer.
          if (!bufferPool.offer(buffer))
              MemoryUtil.clean(buffer);
      }
  
      /**
       * Empties the buffer pool.
       */
      public void emptyBufferPool()
      {
          ByteBuffer buffer = bufferPool.poll();
          while(buffer != null)
          {
              MemoryUtil.clean(buffer);
              buffer = bufferPool.poll();
          }
      }
  
      /**
       * Checks if the number of used buffers has exceeded the maximum number of cached buffers.
       *
       * @return {@code true} if the number of used buffers has exceeded the maximum number of cached buffers,
       * {@code false} otherwise.
       */
      public boolean atLimit()
      {
          return usedBuffers.get() >= maxBufferPoolSize;
      }
  
      @Override
      public String toString()
      {
          return new StringBuilder()
                 .append("SimpleBufferPool:")
                 .append(" usedBuffers:").append(usedBuffers.get())
                 .append(", maxBufferPoolSize:").append(maxBufferPoolSize)
                 .append(", bufferSize:").append(bufferSize)
                 .toString();
      }
  }
  