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.kafka.common.utils;
  
  import java.nio.ByteBuffer;
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * Simple non-threadsafe interface for caching byte buffers. This is suitable for simple cases like ensuring that
   * a given KafkaConsumer reuses the same decompression buffer when iterating over fetched records. For small record
   * batches, allocating a potentially large buffer (64 KB for LZ4) will dominate the cost of decompressing and
   * iterating over the records in the batch.
   */
  public abstract class BufferSupplier implements AutoCloseable {
  
      public static final BufferSupplier NO_CACHING = new BufferSupplier() {
          @Override
          public ByteBuffer get(int capacity) {
              return ByteBuffer.allocate(capacity);
          }
  
          @Override
          public void release(ByteBuffer buffer) {}
  
          @Override
          public void close() {}
      };
  
      public static BufferSupplier create() {
          return new DefaultSupplier();
      }
  
      /**
       * Supply a buffer with the required capacity. This may return a cached buffer or allocate a new instance.
       */
      public abstract ByteBuffer get(int capacity);
  
      /**
       * Return the provided buffer to be reused by a subsequent call to `get`.
       */
      public abstract void release(ByteBuffer buffer);
  
      /**
       * Release all resources associated with this supplier.
       */
      public abstract void close();
  
      private static class DefaultSupplier extends BufferSupplier {
          // We currently use a single block size, so optimise for that case
          private final Map<Integer, Deque<ByteBuffer>> bufferMap = new HashMap<>(1);
  
          @Override
          public ByteBuffer get(int size) {
              Deque<ByteBuffer> bufferQueue = bufferMap.get(size);
              if (bufferQueue == null || bufferQueue.isEmpty())
                  return ByteBuffer.allocate(size);
              else
                  return bufferQueue.pollFirst();
          }
  
          @Override
          public void release(ByteBuffer buffer) {
              buffer.clear();
              // We currently keep a single buffer in flight, so optimise for that case
              Deque<ByteBuffer> bufferQueue = bufferMap.computeIfAbsent(buffer.capacity(), k -> new ArrayDeque<>(1));
              bufferQueue.addLast(buffer);
          }
  
          @Override
          public void close() {
              bufferMap.clear();
          }
      }
  
      /**
       * Simple buffer supplier for single-threaded usage. It caches a single buffer, which grows
       * monotonically as needed to fulfill the allocation request.
       */
      public static class GrowableBufferSupplier extends BufferSupplier {
          private ByteBuffer cachedBuffer;
  
          @Override
          public ByteBuffer get(int minCapacity) {
              if (cachedBuffer != null && cachedBuffer.capacity() >= minCapacity) {
                  ByteBuffer res = cachedBuffer;
                  cachedBuffer = null;
                  return res;
              } else {
                  cachedBuffer = null;
                  return ByteBuffer.allocate(minCapacity);
              }
          }
  
          @Override
          public void release(ByteBuffer buffer) {
              buffer.clear();
              cachedBuffer = buffer;
          }
  
          @Override
          public void close() {
              cachedBuffer = null;
          }
      }
  
  }
  