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.utils.concurrent;
  
  import java.util.ArrayDeque;
  import java.util.Collection;
  import java.util.Objects;
  import java.util.function.Supplier;
  
  
  interface LightweightRecyclerPoolHolder<T>
  {
      ArrayDeque<T> get();
  }
  
  /**
   * A simple thread local object reuse facility with limited capacity and no attempt at rebalancing pooling between
   * threads. This is meant to be put in place where churn is high, but single object allocation and footprint are not
   * so high to justify a more sophisticated approach.
   *
   * @param <T>
   * @see ThreadLocals#createLightweightRecycler(int)
   */
  public interface LightweightRecycler<T> extends LightweightRecyclerPoolHolder<T>
  {
      /**
       * @return a reusable instance, or null if none is available
       */
      default T reuse()
      {
          return get().pollFirst();
      }
  
      /**
       * @return a reusable instance, or allocate one via the provided supplier
       */
      default T reuseOrAllocate(Supplier<T> supplier)
      {
          final T reuse = reuse();
          return reuse != null ? reuse : supplier.get();
      }
  
      /**
       * @param t to be recycled, if t is a collection it will be cleared before recycling, but not cleared if not
       *          recycled
       * @return true if t was recycled, false otherwise
       */
      default boolean tryRecycle(T t)
      {
          Objects.requireNonNull(t);
  
          final ArrayDeque<T> pool = get();
          if (pool.size() < capacity())
          {
              if (t instanceof Collection)
                  ((Collection<?>) t).clear();
              pool.offerFirst(t);
              return true;
          }
          else
          {
              return false;
          }
      }
  
      /**
       * @return current count of available instances for reuse
       */
      default int available()
      {
          return get().size();
      }
  
  
      /**
       * @return maximum capacity of the recycler
       */
      int capacity();
  }
  