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 accord.utils.btree;
  
  public class TinyThreadLocalPool<V> extends ThreadLocal<TinyThreadLocalPool.TinyPool<V>>
  {
      protected TinyPool<V> initialValue()
      {
          return new TinyPool<>();
      }
  
      // a super-simple pool containing at most two items; useful because we primarily use btrees in a two-tier hierarchy
      // so a single thread local item would be insufficient, but an arbitrary length queue too much
      public static class TinyPool<V>
      {
          final Thread thread;
          Object val1, val2, val3;
  
          public TinyPool()
          {
              this.thread = Thread.currentThread();
          }
  
          public void offer(V value)
          {
              if (Thread.currentThread() == thread)
                  offerSafe(value);
          }
          private void offerSafe(V value)
          {
              if (val1 == null) val1 = value;
              else if (val2 == null) val2 = value;
              else if (val3 == null) val3 = value;
          }
          public V poll()
          {
              Object result;
              if (val1 != null)
              {
                  result = val1;
                  val1 = null;
              }
              else if (val2 != null)
              {
                  result = val2;
                  val2 = null;
              }
              else if (val3 != null)
              {
                  result = val3;
                  val3 = null;
              }
              else result = null;
              return (V) result;
          }
      }
  
      public void offer(V value)
      {
          get().offer(value);
      }
  
      public V poll()
      {
          return get().poll();
      }
  }
  