com.google.cloud.dataflow.sdk.util.state.MergedBag.java Source code

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Here is the source code for com.google.cloud.dataflow.sdk.util.state.MergedBag.java

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/*
 * Copyright (C) 2015 Google Inc.
 *
 * 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.google.cloud.dataflow.sdk.util.state;

import com.google.common.collect.Iterables;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * Implementation of {@link BagState} reads from all the sources and writes to the specified result.
 *
 * @param <T> the type of elements in the bag
 */
class MergedBag<T> implements BagState<T> {
    private final Collection<BagState<T>> sources;
    private final BagState<T> result;

    public MergedBag(Collection<BagState<T>> sources, BagState<T> result) {
        this.sources = sources;
        this.result = result;
    }

    @Override
    public void clear() {
        for (State source : sources) {
            source.clear();
        }
        result.clear();
    }

    @Override
    public void add(T input) {
        result.add(input);
    }

    @Override
    public StateContents<Iterable<T>> get() {
        // Initiate the get's right away
        final List<StateContents<Iterable<T>>> futures = new ArrayList<>(sources.size());
        for (BagState<T> source : sources) {
            futures.add(source.get());
        }

        // But defer the actual reads until later.
        return new StateContents<Iterable<T>>() {
            @Override
            public Iterable<T> read() {
                List<Iterable<T>> allIterables = new ArrayList<>();
                for (StateContents<Iterable<T>> future : futures) {
                    allIterables.add(future.read());
                }
                return Iterables.concat(allIterables);
            }
        };
    }

    @Override
    public StateContents<Boolean> isEmpty() {
        // Initiate the get's right away
        final List<StateContents<Boolean>> futures = new ArrayList<>(sources.size());
        for (BagState<T> source : sources) {
            futures.add(source.isEmpty());
        }

        // But defer the actual reads until later.
        return new StateContents<Boolean>() {
            @Override
            public Boolean read() {
                for (StateContents<Boolean> future : futures) {
                    if (!future.read()) {
                        return false;
                    }
                }
                return true;
            }
        };
    }
}