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.activemq.artemis.utils;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.util.internal.MathUtil;
  
  /**
   * Thread-safe {@code <T>} interner.
   * <p>
   * Differently from {@link String#intern()} it contains a fixed amount of entries and when used by concurrent threads it
   * doesn't ensure the uniqueness of the entries ie the same entry could be allocated multiple times by concurrent
   * calls.
   */
  public abstract class AbstractPool<I, O> {
  
     public static final int DEFAULT_POOL_CAPACITY = 32;
  
     private final O[] entries;
     private final int mask;
     private final int shift;
  
     public AbstractPool() {
        this(DEFAULT_POOL_CAPACITY);
     }
  
     public AbstractPool(final int capacity) {
        entries = (O[]) new Object[MathUtil.findNextPositivePowerOfTwo(capacity)];
        mask = entries.length - 1;
        //log2 of entries.length
        shift = 31 - Integer.numberOfLeadingZeros(entries.length);
     }
  
     /**
      * Create a new entry.
      */
     protected abstract O create(I value);
  
     /**
      * {@return {@code true} if the {@code entry} content is equal to {@code value};}
      */
     protected abstract boolean isEqual(O entry, I value);
  
     protected int hashCode(I value) {
        return value.hashCode();
     }
  
     /**
      * Returns and interned entry if possible, a new one otherwise.
      * <p>
      * The {@code byteBuf}'s {@link ByteBuf#readerIndex()} is incremented by {@code length} after it.
      */
     public final O getOrCreate(final I value) {
        if (value == null) {
           return null;
        }
        final int hashCode = hashCode(value);
        //fast % operation with power of 2 entries.length
        final int firstIndex = hashCode & mask;
        final O firstEntry = entries[firstIndex];
        if (isEqual(firstEntry, value)) {
           return firstEntry;
        }
        final int secondIndex = (hashCode >> shift) & mask;
        final O secondEntry = entries[secondIndex];
        if (isEqual(secondEntry, value)) {
           return secondEntry;
        }
        final O internedEntry = create(value);
        final int entryIndex = firstEntry == null ? firstIndex : secondIndex;
        entries[entryIndex] = internedEntry;
        return internedEntry;
     }
  }
  