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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * 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.druid.segment;

import java.io.Closeable;
import java.util.Optional;

/**
 * Interface for an object that may have a reference acquired in the form of a {@link Closeable}. This is intended to be
 * used with an implementation of {@link ReferenceCountingCloseableObject}, or anything else that wishes to provide
 * a method to account for the acquire and release of a reference to the object.
 */
public interface ReferenceCountedObject
{
  /**
   * This method is expected to increment a reference count and provide a {@link Closeable} that decrements the
   * reference count when closed. This is likely just a wrapper around
   * {@link ReferenceCountingCloseableObject#incrementReferenceAndDecrementOnceCloseable()}, but may also include any
   * other associated references which should be incremented when this method is called, and decremented/released by the
   * closeable.
   *
   * IMPORTANT NOTE: to fulfill the contract of this method, implementors must return a closeable to indicate that the
   * reference can be acquired, even if there is nothing to close. Implementors should avoid allowing this method or the
   * {@link Closeable} it creates to throw exceptions.
   *
   * For callers: if this method returns non-empty, IT MUST BE CLOSED, else reference counts can potentially leak.
   */
  Optional acquireReferences();
}