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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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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.cassandra.utils.concurrent;

/**
 * An object that needs ref counting does the two following:
 *   - defines a Tidy object that will cleanup once it's gone,
 *     (this must retain no references to the object we're tracking (only its resources and how to clean up))
 * Then, one of two options:
 * 1) Construct a Ref directly pointing to it, and always use this Ref; or
 * 2)
 *   - implements RefCounted
 *   - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours
 *   - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
 *     (to ensure the selfRef is collected with the object, so that leaks may be detected and corrected)
 */
public interface RefCounted
{
    /**
     * @return the a new Ref() to the managed object, incrementing its refcount, or null if it is already released
     */
    public Ref tryRef();

    public Ref ref();

    public static interface Tidy
    {
        void tidy() throws Exception;
        String name();
    }
}