com.spotify.dns.AggregatingChangeNotifier.java Source code

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Here is the source code for com.spotify.dns.AggregatingChangeNotifier.java

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/*
 * Copyright (c) 2015 Spotify AB
 *
 * Licensed 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 com.spotify.dns;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;

import java.util.List;
import java.util.Set;

/**
 * A {@link ChangeNotifier} that aggregates the records provided by a list of notifiers.
 */
class AggregatingChangeNotifier<T> extends AbstractChangeNotifier<T> {

    private final List<ChangeNotifier<T>> changeNotifiers;

    private volatile Set<T> records = ImmutableSet.of();

    /**
     * Create a new aggregating {@link ChangeNotifier}.
     *
     * @param changeNotifiers the notifiers to aggregate
     */
    AggregatingChangeNotifier(final Iterable<ChangeNotifier<T>> changeNotifiers) {
        this.changeNotifiers = ImmutableList.copyOf(changeNotifiers);

        // Set up forwarding of listeners
        for (final ChangeNotifier<T> changeNotifier : this.changeNotifiers) {
            changeNotifier.setListener(new Listener<T>() {
                @Override
                public void onChange(final ChangeNotification<T> ignored) {
                    checkChange();
                }
            }, false);
        }

        records = aggregateSet();
    }

    @Override
    public Set<T> current() {
        return records;
    }

    @Override
    protected void closeImplementation() {
        for (ChangeNotifier<T> provider : changeNotifiers) {
            provider.close();
        }
    }

    private synchronized void checkChange() {
        Set<T> currentRecords = aggregateSet();

        if (!currentRecords.equals(records)) {
            final ChangeNotification<T> changeNotification = newChangeNotification(currentRecords, records);
            records = currentRecords;

            fireRecordsUpdated(changeNotification);
        }
    }

    private Set<T> aggregateSet() {
        ImmutableSet.Builder<T> records = ImmutableSet.builder();
        for (final ChangeNotifier<T> changeNotifier : changeNotifiers) {
            records.addAll(changeNotifier.current());
        }
        return records.build();
    }
}