org.apache.activemq.artemis.utils.AbstractPool Maven / Gradle / Ivy
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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 org.apache.activemq.artemis.shaded.io.netty.buffer.ByteBuf;
import org.apache.activemq.artemis.shaded.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;
}
}