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| 1 | +package lambdasinaction.appc; |
| 2 | + |
| 3 | +import java.util.*; |
| 4 | +import java.util.concurrent.*; |
| 5 | +import java.util.function.*; |
| 6 | +import java.util.stream.*; |
| 7 | + |
| 8 | +/** |
| 9 | + * Adapted from http://mail.openjdk.java.net/pipermail/lambda-dev/2013-November/011516.html |
| 10 | + */ |
| 11 | +public class StreamForker<T> { |
| 12 | + |
| 13 | + private final Stream<T> stream; |
| 14 | + private final Map<Object, Function<Stream<T>, ?>> forks = new HashMap<>(); |
| 15 | + |
| 16 | + public StreamForker(Stream<T> stream) { |
| 17 | + this.stream = stream; |
| 18 | + } |
| 19 | + |
| 20 | + public StreamForker<T> fork(Object key, Function<Stream<T>, ?> f) { |
| 21 | + forks.put(key, f); |
| 22 | + return this; |
| 23 | + } |
| 24 | + |
| 25 | + public Results getResults() { |
| 26 | + ForkingStreamConsumer<T> consumer = build(); |
| 27 | + try { |
| 28 | + stream.sequential().forEach(consumer); |
| 29 | + } finally { |
| 30 | + consumer.finish(); |
| 31 | + } |
| 32 | + return consumer; |
| 33 | + } |
| 34 | + |
| 35 | + private ForkingStreamConsumer<T> build() { |
| 36 | + List<BlockingQueue<T>> queues = new ArrayList<>(); |
| 37 | + |
| 38 | + Map<Object, Future<?>> actions = |
| 39 | + forks.entrySet().stream().reduce( |
| 40 | + new HashMap<Object, Future<?>>(), |
| 41 | + (map, e) -> { |
| 42 | + map.put(e.getKey(), |
| 43 | + getOperationResult(queues, e.getValue())); |
| 44 | + return map; |
| 45 | + }, |
| 46 | + (m1, m2) -> { |
| 47 | + m1.putAll(m2); |
| 48 | + return m1; |
| 49 | + }); |
| 50 | + |
| 51 | + return new ForkingStreamConsumer<>(queues, actions); |
| 52 | + } |
| 53 | + |
| 54 | + private Future<?> getOperationResult(List<BlockingQueue<T>> queues, Function<Stream<T>, ?> f) { |
| 55 | + BlockingQueue<T> queue = new LinkedBlockingQueue<>(); |
| 56 | + queues.add(queue); |
| 57 | + Spliterator<T> spliterator = new BlockingQueueSpliterator<>(queue); |
| 58 | + Stream<T> source = StreamSupport.stream(spliterator, false); |
| 59 | + return CompletableFuture.supplyAsync( () -> f.apply(source) ); |
| 60 | + } |
| 61 | + |
| 62 | + public static interface Results { |
| 63 | + public <R> R get(Object key); |
| 64 | + } |
| 65 | + |
| 66 | + private static class ForkingStreamConsumer<T> implements Consumer<T>, Results { |
| 67 | + static final Object END_OF_STREAM = new Object(); |
| 68 | + |
| 69 | + private final List<BlockingQueue<T>> queues; |
| 70 | + private final Map<Object, Future<?>> actions; |
| 71 | + |
| 72 | + ForkingStreamConsumer(List<BlockingQueue<T>> queues, Map<Object, Future<?>> actions) { |
| 73 | + this.queues = queues; |
| 74 | + this.actions = actions; |
| 75 | + } |
| 76 | + |
| 77 | + @Override |
| 78 | + public void accept(T t) { |
| 79 | + queues.forEach(q -> q.add(t)); |
| 80 | + } |
| 81 | + |
| 82 | + @Override |
| 83 | + public <R> R get(Object key) { |
| 84 | + try { |
| 85 | + return ((Future<R>) actions.get(key)).get(); |
| 86 | + } catch (Exception e) { |
| 87 | + throw new RuntimeException(e); |
| 88 | + } |
| 89 | + } |
| 90 | + |
| 91 | + void finish() { |
| 92 | + accept((T) END_OF_STREAM); |
| 93 | + } |
| 94 | + } |
| 95 | + |
| 96 | + private static class BlockingQueueSpliterator<T> implements Spliterator<T> { |
| 97 | + private final BlockingQueue<T> q; |
| 98 | + |
| 99 | + BlockingQueueSpliterator(BlockingQueue<T> q) { |
| 100 | + this.q = q; |
| 101 | + } |
| 102 | + |
| 103 | + @Override |
| 104 | + public boolean tryAdvance(Consumer<? super T> action) { |
| 105 | + T t; |
| 106 | + while (true) { |
| 107 | + try { |
| 108 | + t = q.take(); |
| 109 | + break; |
| 110 | + } |
| 111 | + catch (InterruptedException e) { |
| 112 | + } |
| 113 | + } |
| 114 | + |
| 115 | + if (t != ForkingStreamConsumer.END_OF_STREAM) { |
| 116 | + action.accept(t); |
| 117 | + return true; |
| 118 | + } |
| 119 | + |
| 120 | + return false; |
| 121 | + } |
| 122 | + |
| 123 | + @Override |
| 124 | + public Spliterator<T> trySplit() { |
| 125 | + return null; |
| 126 | + } |
| 127 | + |
| 128 | + @Override |
| 129 | + public long estimateSize() { |
| 130 | + return 0; |
| 131 | + } |
| 132 | + |
| 133 | + @Override |
| 134 | + public int characteristics() { |
| 135 | + return 0; |
| 136 | + } |
| 137 | + } |
| 138 | +} |
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