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/**
 * 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 } interner.
 * 

* 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 { 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); /** * Returns {@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. *

* 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; } }





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