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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.locator;

import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.utils.FBUtilities;
import java.util.function.Predicate;

public class InOurDcTester
{
    private static ReplicaTester replicas;
    private static EndpointTester endpoints;

    final String dc;
    final IEndpointSnitch snitch;

    private InOurDcTester(String dc, IEndpointSnitch snitch)
    {
        this.dc = dc;
        this.snitch = snitch;
    }

    boolean stale()
    {
        return dc != DatabaseDescriptor.getLocalDataCenter()
                || snitch != DatabaseDescriptor.getEndpointSnitch()
                // this final clause checks if somehow the snitch/localDc have got out of whack;
                // presently, this is possible but very unlikely, but this check will also help
                // resolve races on these global fields as well
                || !dc.equals(snitch.getLocalDatacenter());
    }

    private static final class ReplicaTester extends InOurDcTester implements Predicate
    {
        private ReplicaTester(String dc, IEndpointSnitch snitch)
        {
            super(dc, snitch);
        }

        @Override
        public boolean test(Replica replica)
        {
            return dc.equals(snitch.getDatacenter(replica.endpoint()));
        }
    }

    private static final class EndpointTester extends InOurDcTester implements Predicate
    {
        private EndpointTester(String dc, IEndpointSnitch snitch)
        {
            super(dc, snitch);
        }

        @Override
        public boolean test(InetAddressAndPort endpoint)
        {
            return dc.equals(snitch.getDatacenter(endpoint));
        }
    }

    public static Predicate replicas()
    {
        ReplicaTester cur = replicas;
        if (cur == null || cur.stale())
            replicas = cur = new ReplicaTester(DatabaseDescriptor.getLocalDataCenter(), DatabaseDescriptor.getEndpointSnitch());
        return cur;
    }

    public static Predicate endpoints()
    {
        EndpointTester cur = endpoints;
        if (cur == null || cur.stale())
            endpoints = cur = new EndpointTester(DatabaseDescriptor.getLocalDataCenter(), DatabaseDescriptor.getEndpointSnitch());
        return cur;
    }

}