util/concurrent/Flow.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.ArrayList;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.stream.Stream;

/**
 * Interrelated interfaces and static methods for establishing
 * flow-controlled components in which {@link Publisher Publishers}
 * produce items consumed by one or more {@link Subscriber
 * Subscribers}, each managed by a {@link Subscription
 * Subscription}.
 *
 * <p>These interfaces correspond to the <a
 * href="http://www.reactive-streams.org/"> reactive-streams</a>
 * specification.  They apply in both concurrent and distributed
 * asynchronous settings: All (seven) methods are defined in {@code
 * void} "oneway" message style. Communication relies on a simple form
 * of flow control (method {@link Subscription#request}) that can be
 * used to avoid resource management problems that may otherwise occur
 * in "push" based systems.
 *
 * <p><b>Examples.</b> A {@link Publisher} usually defines its own
 * {@link Subscription} implementation; constructing one in method
 * {@code subscribe} and issuing it to the calling {@link
 * Subscriber}. It publishes items to the subscriber asynchronously,
 * normally using an {@link Executor}.  For example, here is a very
 * simple publisher that only issues (when requested) a single {@code
 * TRUE} item to a single subscriber.  Because the subscriber receives
 * only a single item, this class does not use buffering and ordering
 * control required in most implementations (for example {@link
 * SubmissionPublisher}).
 *
 * <pre> {@code
 * class OneShotPublisher implements Publisher<Boolean> {
 *   final Executor executor = ForkJoinPool.commonPool(); // daemon-based
 *   boolean subscribed = false; // true after first subscribe
 *   public synchronized void subscribe(Subscriber<? super Boolean> subscriber) {
 *     if (subscribed)
 *        subscriber.onError(new IllegalStateException()); // only one allowed
 *     else {
 *       subscribed = true;
 *       subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
 *     }
 *   }
 *   static class OneShotSubscription implements Subscription {
 *     final Subscriber<? super Boolean> subscriber;
 *     final Executor executor;
 *     boolean completed = false;
 *     OneShotSubscription(Subscriber<? super Boolean> subscriber,
 *                         Executor executor) {
 *       this.subscriber = subscriber;
 *       this.executor = executor;
 *     }
 *     public synchronized void request(long n) {
 *       if (n != 0 && !completed) {
 *         completed = true;
 *         executor.execute(() -> {
 *           if (n < 0)
 *             subscriber.onError(new IllegalArgumentException());
 *           else {
 *             subscriber.onNext(Boolean.TRUE);
 *             subscriber.onComplete();
 *           }});
 *       }
 *     }
 *     public synchronized void cancel() {
 *       completed = true; // ineffective if task already started
 *     }
 *   }
 * }}</pre>
 *
 * <p>A {@link Subscriber} arranges that items be requested and
 * processed.  Items (invocations of {@link Subscriber#onNext}) are
 * not issued unless requested, but multiple items may be requested.
 * Many Subscriber implementations can arrange this in the style of
 * the following example, where a buffer size of 1 single-steps, and
 * larger sizes usually allow for more efficient overlapped processing
 * with less communication; for example with a value of 64, this keeps
 * total outstanding requests between 32 and 64.  (See also {@link
 * #consume(long, Publisher, Consumer)} that automates a common case.)
 * Because Subscriber method invocations for a given {@link
 * Subscription} are strictly ordered, there is no need for these
 * methods to use locks or volatiles unless a Subscriber maintains
 * multiple Subscriptions (in which case it is better to instead
 * define multiple Subscribers, each with its own Subscription).
 *
 * <pre> {@code
 * class SampleSubscriber<T> implements Subscriber<T> {
 *   final Consumer<? super T> consumer;
 *   Subscription subscription;
 *   final long bufferSize;
 *   long count;
 *   SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
 *     this.bufferSize = bufferSize;
 *     this.consumer = consumer;
 *   }
 *   public void onSubscribe(Subscription subscription) {
 *     (this.subscription = subscription).request(bufferSize);
 *     count = bufferSize - bufferSize / 2; // re-request when half consumed
 *   }
 *   public void onNext(T item) {
 *     if (--count <= 0)
 *       subscription.request(count = bufferSize - bufferSize / 2);
 *     consumer.accept(item);
 *   }
 *   public void onError(Throwable ex) { ex.printStackTrace(); }
 *   public void onComplete() {}
 * }}</pre>
 *
 * <p>When flow control is inapplicable, a subscriber may initially
 * request an effectively unbounded number of items, as in:
 *
 * <pre> {@code
 * class UnboundedSubscriber<T> implements Subscriber<T> {
 *   public void onSubscribe(Subscription subscription) {
 *     subscription.request(Long.MAX_VALUE); // effectively unbounded
 *   }
 *   public void onNext(T item) { use(item); }
 *   public void onError(Throwable ex) { ex.printStackTrace(); }
 *   public void onComplete() {}
 *   void use(T item) { ... }
 * }}</pre>
 *
 * @author Doug Lea
 * @since 1.9
 */
public final class Flow {

    private Flow() {} // uninstantiable

    /**
     * A producer of items (and related control messages) received by
     * Subscribers.  Each current {@link Subscriber} receives the same
     * items (via method {@code onNext}) in the same order, unless
     * drops or errors are encountered. If a Publisher encounters an
     * error that does not allow items to be issued to a Subscriber,
     * that Subscriber receives {@code onError}, and then receives no
     * further messages.  Otherwise, when it is known that no further
     * messages will be issued to it, a subscriber receives {@code
     * onComplete}.  Publishers ensure that Subscriber method
     * invocations for each subscription are strictly ordered in <a
     * href="package-summary.html#MemoryVisibility"><i>happens-before</i></a>
     * order.
     *
     * <p>Publishers may vary in policy about whether drops (failures
     * to issue an item because of resource limitations) are treated
     * as unrecoverable errors.  Publishers may also vary about
     * whether Subscribers receive items that were produced or
     * available before they subscribed.
     *
     * @param <T> the published item type
     */
    @FunctionalInterface
    public static interface Publisher<T> {
        /**
         * Adds the given Subscriber if possible.  If already
         * subscribed, or the attempt to subscribe fails due to policy
         * violations or errors, the Subscriber's {@code onError}
         * method is invoked with an {@link IllegalStateException}.
         * Otherwise, the Subscriber's {@code onSubscribe} method is
         * invoked with a new {@link Subscription}.  Subscribers may
         * enable receiving items by invoking the {@code request}
         * method of this Subscription, and may unsubscribe by
         * invoking its {@code cancel} method.
         *
         * @param subscriber the subscriber
         * @throws NullPointerException if subscriber is null
         */
        public void subscribe(Subscriber<? super T> subscriber);
    }

    /**
     * A receiver of messages.  The methods in this interface are
     * invoked in strict sequential order for each {@link
     * Subscription}.
     *
     * @param <T> the subscribed item type
     */
    public static interface Subscriber<T> {
        /**
         * Method invoked prior to invoking any other Subscriber
         * methods for the given Subscription. If this method throws
         * an exception, resulting behavior is not guaranteed, but may
         * cause the Subscription to be cancelled.
         *
         * <p>Typically, implementations of this method invoke {@code
         * subscription.request} to enable receiving items.
         *
         * @param subscription a new subscription
         */
        public void onSubscribe(Subscription subscription);

        /**
         * Method invoked with a Subscription's next item.  If this
         * method throws an exception, resulting behavior is not
         * guaranteed, but may cause the Subscription to be cancelled.
         *
         * @param item the item
         */
        public void onNext(T item);

        /**
         * Method invoked upon an unrecoverable error encountered by a
         * Publisher or Subscription, after which no other Subscriber
         * methods are invoked by the Subscription.  If this method
         * itself throws an exception, resulting behavior is
         * undefined.
         *
         * @param throwable the exception
         */
        public void onError(Throwable throwable);

        /**
         * Method invoked when it is known that no additional
         * Subscriber method invocations will occur for a Subscription
         * that is not already terminated by error, after which no
         * other Subscriber methods are invoked by the Subscription.
         * If this method throws an exception, resulting behavior is
         * undefined.
         */
        public void onComplete();
    }

    /**
     * Message control linking a {@link Publisher} and {@link
     * Subscriber}.  Subscribers receive items only when requested,
     * and may cancel at any time. The methods in this interface are
     * intended to be invoked only by their Subscribers; usages in
     * other contexts have undefined effects.
     */
    public static interface Subscription {
        /**
         * Adds the given number {@code n} of items to the current
         * unfulfilled demand for this subscription.  If {@code n} is
         * negative, the Subscriber will receive an {@code onError}
         * signal with an {@link IllegalArgumentException}
         * argument. Otherwise, the Subscriber will receive up to
         * {@code n} additional {@code onNext} invocations (or fewer
         * if terminated).
         *
         * @param n the increment of demand; a value of {@code
         * Long.MAX_VALUE} may be considered as effectively unbounded
         */
        public void request(long n);

        /**
         * Causes the Subscriber to (eventually) stop receiving
         * messages.  Implementation is best-effort -- additional
         * messages may be received after invoking this method.  A
         * cancelled subscription need not ever receive an {@code
         * onComplete} signal.
         */
        public void cancel();
    }

    /**
     * A component that acts as both a Subscriber and Publisher.
     *
     * @param <T> the subscribed item type
     * @param <R> the published item type
     */
    public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
    }

    // Support for static methods

    static final long DEFAULT_BUFFER_SIZE = 64L;

    abstract static class CompletableSubscriber<T,U> implements Subscriber<T>,
                                                                Consumer<T> {
        final CompletableFuture<U> status;
        Subscription subscription;
        long requestSize;
        long count;
        CompletableSubscriber(long bufferSize, CompletableFuture<U> status) {
            this.status = status;
            this.requestSize = bufferSize;
        }
        public final void onSubscribe(Subscription subscription) {
            (this.subscription = subscription).request(requestSize);
            count = requestSize -= (requestSize >>> 1);
        }
        public final void onError(Throwable ex) {
            status.completeExceptionally(ex);
        }
        public void onNext(T item) {
            try {
                if (--count <= 0)
                    subscription.request(count = requestSize);
                accept(item);
            } catch (Throwable ex) {
                status.completeExceptionally(ex);
            }
        }
    }

    static final class ConsumeSubscriber<T> extends CompletableSubscriber<T,Void> {
        final Consumer<? super T> consumer;
        ConsumeSubscriber(long bufferSize,
                          CompletableFuture<Void> status,
                          Consumer<? super T> consumer) {
            super(bufferSize, status);
            this.consumer = consumer;
        }
        public void accept(T item) { consumer.accept(item); }
        public void onComplete() { status.complete(null); }
    }

    /**
     * Creates and subscribes a Subscriber that consumes all items
     * from the given publisher using the given Consumer function, and
     * using the given bufferSize for buffering. Returns a
     * CompletableFuture that is completed normally when the publisher
     * signals {@code onComplete}, or completed exceptionally upon any
     * error, including an exception thrown by the Consumer (in which
     * case the subscription is cancelled if not already terminated).
     *
     * @param <T> the published item type
     * @param bufferSize the request size for subscriptions
     * @param publisher the publisher
     * @param consumer the function applied to each onNext item
     * @return a CompletableFuture that is completed normally
     * when the publisher signals onComplete, and exceptionally
     * upon any error
     * @throws NullPointerException if publisher or consumer are null
     * @throws IllegalArgumentException if bufferSize not positive
     */
    public static <T> CompletableFuture<Void> consume(
        long bufferSize, Publisher<T> publisher, Consumer<? super T> consumer) {
        if (bufferSize <= 0L)
            throw new IllegalArgumentException("bufferSize must be positive");
        if (publisher == null || consumer == null)
            throw new NullPointerException();
        CompletableFuture<Void> status = new CompletableFuture<>();
        publisher.subscribe(new ConsumeSubscriber<T>(
                                bufferSize, status, consumer));
        return status;
    }

    /**
     * Equivalent to {@link #consume(long, Publisher, Consumer)}
     * with a buffer size of 64.
     *
     * @param <T> the published item type
     * @param publisher the publisher
     * @param consumer the function applied to each onNext item
     * @return a CompletableFuture that is completed normally
     * when the publisher signals onComplete, and exceptionally
     * upon any error
     * @throws NullPointerException if publisher or consumer are null
     */
    public static <T> CompletableFuture<Void> consume(
        Publisher<T> publisher, Consumer<? super T> consumer) {
        return consume(DEFAULT_BUFFER_SIZE, publisher, consumer);
    }

    /**
     * Temporary implementation for Stream, collecting all items
     * and then applying stream operation.
     */
    static final class StreamSubscriber<T,R> extends CompletableSubscriber<T,R> {
        final Function<? super Stream<T>, ? extends R> fn;
        final ArrayList<T> items;
        StreamSubscriber(long bufferSize,
                         CompletableFuture<R> status,
                         Function<? super Stream<T>, ? extends R> fn) {
            super(bufferSize, status);
            this.fn = fn;
            this.items = new ArrayList<T>();
        }
        public void accept(T item) { items.add(item); }
        public void onComplete() { status.complete(fn.apply(items.stream())); }
    }

    /**
     * Creates and subscribes a Subscriber that applies the given
     * stream operation to items, and uses the given bufferSize for
     * buffering. Returns a CompletableFuture that is completed
     * normally with the result of this function when the publisher
     * signals {@code onComplete}, or is completed exceptionally upon
     * any error.
     *
     * <p><b>Preliminary release note:</b> Currently, this method
     * collects all items before executing the stream
     * computation. Improvements are pending Stream integration.
     *
     * @param <T> the published item type
     * @param <R> the result type of the stream function
     * @param bufferSize the request size for subscriptions
     * @param publisher the publisher
     * @param streamFunction the operation on elements
     * @return a CompletableFuture that is completed normally with the
     * result of the given function as result when the publisher signals
     * onComplete, and exceptionally upon any error
     * @throws NullPointerException if publisher or function are null
     * @throws IllegalArgumentException if bufferSize not positive
     */
    public static <T,R> CompletableFuture<R> stream(
        long bufferSize, Publisher<T> publisher,
        Function<? super Stream<T>, ? extends R> streamFunction) {
        if (bufferSize <= 0L)
            throw new IllegalArgumentException("bufferSize must be positive");
        if (publisher == null || streamFunction == null)
            throw new NullPointerException();
        CompletableFuture<R> status = new CompletableFuture<>();
        publisher.subscribe(new StreamSubscriber<T,R>(
                                bufferSize, status, streamFunction));
        return status;
    }

    /**
     * Equivalent to {@link #stream(long, Publisher, Function)}
     * with a buffer size of 64.
     *
     * @param <T> the published item type
     * @param <R> the result type of the stream function
     * @param publisher the publisher
     * @param streamFunction the operation on elements
     * @return a CompletableFuture that is completed normally with the
     * result of the given function as result when the publisher signals
     * onComplete, and exceptionally upon any error
     * @throws NullPointerException if publisher or function are null
     */
    public static <T,R> CompletableFuture<R> stream(
        Publisher<T> publisher,
        Function<? super Stream<T>,? extends R> streamFunction) {
        return stream(DEFAULT_BUFFER_SIZE, publisher, streamFunction);
    }
}
Revision:	1.16
Committed:	Mon Jan 19 18:06:23 2015 UTC (9 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.15:	+19 -14 lines
Log Message:	Improve example
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util.concurrent;
8	jsr166	1.9
9			import java.util.ArrayList;
10	dl	1.1	import java.util.function.Consumer;
11			import java.util.function.Function;
12			import java.util.stream.Stream;
13
14			/**
15			* Interrelated interfaces and static methods for establishing
16			* flow-controlled components in which {@link Publisher Publishers}
17			* produce items consumed by one or more {@link Subscriber
18			* Subscribers}, each managed by a {@link Subscription
19	dl	1.14	* Subscription}.
20	jsr166	1.2	*
21	dl	1.1	* <p>These interfaces correspond to the <a
22			* href="http://www.reactive-streams.org/"> reactive-streams</a>
23	dl	1.14	* specification. They apply in both concurrent and distributed
24			* asynchronous settings: All (seven) methods are defined in {@code
25			* void} "oneway" message style. Communication relies on a simple form
26			* of flow control (method {@link Subscription#request}) that can be
27			* used to avoid resource management problems that may otherwise occur
28			* in "push" based systems.
29	dl	1.1	*
30	dl	1.10	* <p><b>Examples.</b> A {@link Publisher} usually defines its own
31			* {@link Subscription} implementation; constructing one in method
32			* {@code subscribe} and issuing it to the calling {@link
33			* Subscriber}. It publishes items to the subscriber asynchronously,
34			* normally using an {@link Executor}. For example, here is a very
35			* simple publisher that only issues (when requested) a single {@code
36	dl	1.16	* TRUE} item to a single subscriber. Because the subscriber receives
37			* only a single item, this class does not use buffering and ordering
38			* control required in most implementations (for example {@link
39			* SubmissionPublisher}).
40	dl	1.10	*
41			* <pre> {@code
42			* class OneShotPublisher implements Publisher<Boolean> {
43	dl	1.15	* final Executor executor = ForkJoinPool.commonPool(); // daemon-based
44	dl	1.16	* boolean subscribed = false; // true after first subscribe
45			* public synchronized void subscribe(Subscriber<? super Boolean> subscriber) {
46			* if (subscribed)
47			* subscriber.onError(new IllegalStateException()); // only one allowed
48			* else {
49			* subscribed = true;
50	dl	1.11	* subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
51	dl	1.16	* }
52	dl	1.10	* }
53			* static class OneShotSubscription implements Subscription {
54			* final Subscriber<? super Boolean> subscriber;
55			* final Executor executor;
56	dl	1.16	* boolean completed = false;
57	dl	1.10	* OneShotSubscription(Subscriber<? super Boolean> subscriber,
58			* Executor executor) {
59			* this.subscriber = subscriber;
60			* this.executor = executor;
61			* }
62			* public synchronized void request(long n) {
63	dl	1.16	* if (n != 0 && !completed) {
64	dl	1.10	* completed = true;
65			* executor.execute(() -> {
66	dl	1.16	* if (n < 0)
67			* subscriber.onError(new IllegalArgumentException());
68			* else {
69			* subscriber.onNext(Boolean.TRUE);
70			* subscriber.onComplete();
71			* }});
72	dl	1.10	* }
73			* }
74	dl	1.15	* public synchronized void cancel() {
75			* completed = true; // ineffective if task already started
76			* }
77	dl	1.10	* }
78			* }}</pre>
79			*
80	jsr166	1.13	* <p>A {@link Subscriber} arranges that items be requested and
81	dl	1.10	* processed. Items (invocations of {@link Subscriber#onNext}) are
82			* not issued unless requested, but multiple items may be requested.
83			* Many Subscriber implementations can arrange this in the style of
84			* the following example, where a buffer size of 1 single-steps, and
85			* larger sizes usually allow for more efficient overlapped processing
86			* with less communication; for example with a value of 64, this keeps
87			* total outstanding requests between 32 and 64. (See also {@link
88			* #consume(long, Publisher, Consumer)} that automates a common case.)
89	dl	1.14	* Because Subscriber method invocations for a given {@link
90			* Subscription} are strictly ordered, there is no need for these
91			* methods to use locks or volatiles unless a Subscriber maintains
92			* multiple Subscriptions (in which case it is better to instead
93			* define multiple Subscribers, each with its own Subscription).
94	dl	1.10	*
95			* <pre> {@code
96			* class SampleSubscriber<T> implements Subscriber<T> {
97			* final Consumer<? super T> consumer;
98			* Subscription subscription;
99			* final long bufferSize;
100			* long count;
101			* SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
102			* this.bufferSize = bufferSize;
103			* this.consumer = consumer;
104			* }
105			* public void onSubscribe(Subscription subscription) {
106			* (this.subscription = subscription).request(bufferSize);
107			* count = bufferSize - bufferSize / 2; // re-request when half consumed
108			* }
109			* public void onNext(T item) {
110			* if (--count <= 0)
111			* subscription.request(count = bufferSize - bufferSize / 2);
112			* consumer.accept(item);
113			* }
114			* public void onError(Throwable ex) { ex.printStackTrace(); }
115			* public void onComplete() {}
116			* }}</pre>
117	dl	1.1	*
118	dl	1.14	* <p>When flow control is inapplicable, a subscriber may initially
119	dl	1.12	* request an effectively unbounded number of items, as in:
120			*
121			* <pre> {@code
122			* class UnboundedSubscriber<T> implements Subscriber<T> {
123			* public void onSubscribe(Subscription subscription) {
124			* subscription.request(Long.MAX_VALUE); // effectively unbounded
125			* }
126			* public void onNext(T item) { use(item); }
127			* public void onError(Throwable ex) { ex.printStackTrace(); }
128			* public void onComplete() {}
129			* void use(T item) { ... }
130			* }}</pre>
131	jsr166	1.13	*
132	dl	1.1	* @author Doug Lea
133			* @since 1.9
134			*/
135			public final class Flow {
136
137			private Flow() {} // uninstantiable
138
139			/**
140			* A producer of items (and related control messages) received by
141			* Subscribers. Each current {@link Subscriber} receives the same
142	dl	1.14	* items (via method {@code onNext}) in the same order, unless
143			* drops or errors are encountered. If a Publisher encounters an
144	dl	1.15	* error that does not allow items to be issued to a Subscriber,
145			* that Subscriber receives {@code onError}, and then receives no
146			* further messages. Otherwise, when it is known that no further
147			* messages will be issued to it, a subscriber receives {@code
148			* onComplete}. Publishers ensure that Subscriber method
149	dl	1.14	* invocations for each subscription are strictly ordered in <a
150			* href="package-summary.html#MemoryVisibility"><i>happens-before</i></a>
151			* order.
152			*
153	dl	1.15	* <p>Publishers may vary in policy about whether drops (failures
154			* to issue an item because of resource limitations) are treated
155			* as unrecoverable errors. Publishers may also vary about
156			* whether Subscribers receive items that were produced or
157			* available before they subscribed.
158	dl	1.1	*
159			* @param <T> the published item type
160			*/
161			@FunctionalInterface
162			public static interface Publisher<T> {
163			/**
164			* Adds the given Subscriber if possible. If already
165			* subscribed, or the attempt to subscribe fails due to policy
166	dl	1.14	* violations or errors, the Subscriber's {@code onError}
167			* method is invoked with an {@link IllegalStateException}.
168			* Otherwise, the Subscriber's {@code onSubscribe} method is
169			* invoked with a new {@link Subscription}. Subscribers may
170			* enable receiving items by invoking the {@code request}
171			* method of this Subscription, and may unsubscribe by
172			* invoking its {@code cancel} method.
173	dl	1.1	*
174			* @param subscriber the subscriber
175			* @throws NullPointerException if subscriber is null
176			*/
177			public void subscribe(Subscriber<? super T> subscriber);
178			}
179
180			/**
181	dl	1.14	* A receiver of messages. The methods in this interface are
182			* invoked in strict sequential order for each {@link
183			* Subscription}.
184	dl	1.1	*
185			* @param <T> the subscribed item type
186			*/
187			public static interface Subscriber<T> {
188			/**
189			* Method invoked prior to invoking any other Subscriber
190			* methods for the given Subscription. If this method throws
191			* an exception, resulting behavior is not guaranteed, but may
192			* cause the Subscription to be cancelled.
193			*
194	dl	1.15	* <p>Typically, implementations of this method invoke {@code
195			* subscription.request} to enable receiving items.
196	dl	1.1	*
197			* @param subscription a new subscription
198			*/
199			public void onSubscribe(Subscription subscription);
200
201			/**
202			* Method invoked with a Subscription's next item. If this
203			* method throws an exception, resulting behavior is not
204			* guaranteed, but may cause the Subscription to be cancelled.
205			*
206			* @param item the item
207			*/
208			public void onNext(T item);
209
210			/**
211			* Method invoked upon an unrecoverable error encountered by a
212			* Publisher or Subscription, after which no other Subscriber
213			* methods are invoked by the Subscription. If this method
214			* itself throws an exception, resulting behavior is
215			* undefined.
216			*
217			* @param throwable the exception
218			*/
219			public void onError(Throwable throwable);
220
221			/**
222	dl	1.15	* Method invoked when it is known that no additional
223			* Subscriber method invocations will occur for a Subscription
224			* that is not already terminated by error, after which no
225			* other Subscriber methods are invoked by the Subscription.
226			* If this method throws an exception, resulting behavior is
227	dl	1.14	* undefined.
228	dl	1.1	*/
229			public void onComplete();
230			}
231
232			/**
233	dl	1.14	* Message control linking a {@link Publisher} and {@link
234			* Subscriber}. Subscribers receive items only when requested,
235			* and may cancel at any time. The methods in this interface are
236			* intended to be invoked only by their Subscribers; usages in
237			* other contexts have undefined effects.
238	dl	1.1	*/
239			public static interface Subscription {
240			/**
241			* Adds the given number {@code n} of items to the current
242			* unfulfilled demand for this subscription. If {@code n} is
243	dl	1.14	* negative, the Subscriber will receive an {@code onError}
244			* signal with an {@link IllegalArgumentException}
245			* argument. Otherwise, the Subscriber will receive up to
246			* {@code n} additional {@code onNext} invocations (or fewer
247			* if terminated).
248	dl	1.1	*
249			* @param n the increment of demand; a value of {@code
250			* Long.MAX_VALUE} may be considered as effectively unbounded
251			*/
252			public void request(long n);
253
254			/**
255	dl	1.14	* Causes the Subscriber to (eventually) stop receiving
256	dl	1.15	* messages. Implementation is best-effort -- additional
257			* messages may be received after invoking this method. A
258			* cancelled subscription need not ever receive an {@code
259			* onComplete} signal.
260	dl	1.1	*/
261			public void cancel();
262			}
263
264			/**
265	jsr166	1.2	* A component that acts as both a Subscriber and Publisher.
266	dl	1.1	*
267	jsr166	1.2	* @param <T> the subscribed item type
268			* @param <R> the published item type
269			*/
270	jsr166	1.5	public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
271	dl	1.1	}
272
273			// Support for static methods
274
275	dl	1.10	static final long DEFAULT_BUFFER_SIZE = 64L;
276	dl	1.1
277	jsr166	1.3	abstract static class CompletableSubscriber<T,U> implements Subscriber<T>,
278	dl	1.1	Consumer<T> {
279			final CompletableFuture<U> status;
280			Subscription subscription;
281	dl	1.10	long requestSize;
282	jsr166	1.2	long count;
283	dl	1.10	CompletableSubscriber(long bufferSize, CompletableFuture<U> status) {
284	dl	1.1	this.status = status;
285	dl	1.10	this.requestSize = bufferSize;
286	dl	1.1	}
287			public final void onSubscribe(Subscription subscription) {
288			(this.subscription = subscription).request(requestSize);
289	dl	1.10	count = requestSize -= (requestSize >>> 1);
290	dl	1.1	}
291	jsr166	1.2	public final void onError(Throwable ex) {
292	dl	1.1	status.completeExceptionally(ex);
293			}
294			public void onNext(T item) {
295	dl	1.10	try {
296			if (--count <= 0)
297			subscription.request(count = requestSize);
298			accept(item);
299			} catch (Throwable ex) {
300			status.completeExceptionally(ex);
301	dl	1.1	}
302			}
303			}
304	jsr166	1.2
305	dl	1.1	static final class ConsumeSubscriber<T> extends CompletableSubscriber<T,Void> {
306			final Consumer<? super T> consumer;
307	dl	1.10	ConsumeSubscriber(long bufferSize,
308	dl	1.1	CompletableFuture<Void> status,
309			Consumer<? super T> consumer) {
310	dl	1.10	super(bufferSize, status);
311	dl	1.1	this.consumer = consumer;
312			}
313			public void accept(T item) { consumer.accept(item); }
314			public void onComplete() { status.complete(null); }
315			}
316
317			/**
318			* Creates and subscribes a Subscriber that consumes all items
319			* from the given publisher using the given Consumer function, and
320	dl	1.10	* using the given bufferSize for buffering. Returns a
321	dl	1.1	* CompletableFuture that is completed normally when the publisher
322	dl	1.14	* signals {@code onComplete}, or completed exceptionally upon any
323			* error, including an exception thrown by the Consumer (in which
324			* case the subscription is cancelled if not already terminated).
325	dl	1.1	*
326	jsr166	1.4	* @param <T> the published item type
327	dl	1.10	* @param bufferSize the request size for subscriptions
328	dl	1.1	* @param publisher the publisher
329			* @param consumer the function applied to each onNext item
330			* @return a CompletableFuture that is completed normally
331			* when the publisher signals onComplete, and exceptionally
332	jsr166	1.7	* upon any error
333	dl	1.1	* @throws NullPointerException if publisher or consumer are null
334	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
335	dl	1.1	*/
336			public static <T> CompletableFuture<Void> consume(
337	dl	1.10	long bufferSize, Publisher<T> publisher, Consumer<? super T> consumer) {
338			if (bufferSize <= 0L)
339			throw new IllegalArgumentException("bufferSize must be positive");
340	dl	1.1	if (publisher == null \|\| consumer == null)
341			throw new NullPointerException();
342			CompletableFuture<Void> status = new CompletableFuture<>();
343			publisher.subscribe(new ConsumeSubscriber<T>(
344	dl	1.10	bufferSize, status, consumer));
345	dl	1.1	return status;
346			}
347
348			/**
349			* Equivalent to {@link #consume(long, Publisher, Consumer)}
350	dl	1.10	* with a buffer size of 64.
351	dl	1.1	*
352	jsr166	1.4	* @param <T> the published item type
353	dl	1.1	* @param publisher the publisher
354			* @param consumer the function applied to each onNext item
355			* @return a CompletableFuture that is completed normally
356			* when the publisher signals onComplete, and exceptionally
357	jsr166	1.7	* upon any error
358	dl	1.1	* @throws NullPointerException if publisher or consumer are null
359			*/
360			public static <T> CompletableFuture<Void> consume(
361			Publisher<T> publisher, Consumer<? super T> consumer) {
362	dl	1.10	return consume(DEFAULT_BUFFER_SIZE, publisher, consumer);
363	dl	1.1	}
364
365			/**
366			* Temporary implementation for Stream, collecting all items
367			* and then applying stream operation.
368			*/
369			static final class StreamSubscriber<T,R> extends CompletableSubscriber<T,R> {
370			final Function<? super Stream<T>, ? extends R> fn;
371			final ArrayList<T> items;
372	dl	1.10	StreamSubscriber(long bufferSize,
373	dl	1.1	CompletableFuture<R> status,
374			Function<? super Stream<T>, ? extends R> fn) {
375	dl	1.10	super(bufferSize, status);
376	dl	1.1	this.fn = fn;
377			this.items = new ArrayList<T>();
378			}
379			public void accept(T item) { items.add(item); }
380			public void onComplete() { status.complete(fn.apply(items.stream())); }
381			}
382
383			/**
384			* Creates and subscribes a Subscriber that applies the given
385	dl	1.10	* stream operation to items, and uses the given bufferSize for
386	dl	1.1	* buffering. Returns a CompletableFuture that is completed
387			* normally with the result of this function when the publisher
388	dl	1.14	* signals {@code onComplete}, or is completed exceptionally upon
389			* any error.
390	dl	1.1	*
391			* <p><b>Preliminary release note:</b> Currently, this method
392			* collects all items before executing the stream
393			* computation. Improvements are pending Stream integration.
394			*
395	jsr166	1.4	* @param <T> the published item type
396			* @param <R> the result type of the stream function
397	dl	1.10	* @param bufferSize the request size for subscriptions
398	dl	1.1	* @param publisher the publisher
399			* @param streamFunction the operation on elements
400			* @return a CompletableFuture that is completed normally with the
401			* result of the given function as result when the publisher signals
402	jsr166	1.7	* onComplete, and exceptionally upon any error
403	dl	1.1	* @throws NullPointerException if publisher or function are null
404	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
405	dl	1.1	*/
406			public static <T,R> CompletableFuture<R> stream(
407	dl	1.10	long bufferSize, Publisher<T> publisher,
408	dl	1.1	Function<? super Stream<T>, ? extends R> streamFunction) {
409	dl	1.10	if (bufferSize <= 0L)
410			throw new IllegalArgumentException("bufferSize must be positive");
411	dl	1.1	if (publisher == null \|\| streamFunction == null)
412			throw new NullPointerException();
413			CompletableFuture<R> status = new CompletableFuture<>();
414			publisher.subscribe(new StreamSubscriber<T,R>(
415	dl	1.10	bufferSize, status, streamFunction));
416	dl	1.1	return status;
417			}
418	jsr166	1.2
419	dl	1.1	/**
420			* Equivalent to {@link #stream(long, Publisher, Function)}
421	dl	1.10	* with a buffer size of 64.
422	dl	1.1	*
423	jsr166	1.4	* @param <T> the published item type
424			* @param <R> the result type of the stream function
425	dl	1.1	* @param publisher the publisher
426			* @param streamFunction the operation on elements
427			* @return a CompletableFuture that is completed normally with the
428			* result of the given function as result when the publisher signals
429	jsr166	1.7	* onComplete, and exceptionally upon any error
430	dl	1.1	* @throws NullPointerException if publisher or function are null
431			*/
432			public static <T,R> CompletableFuture<R> stream(
433	jsr166	1.2	Publisher<T> publisher,
434	dl	1.1	Function<? super Stream<T>,? extends R> streamFunction) {
435	dl	1.10	return stream(DEFAULT_BUFFER_SIZE, publisher, streamFunction);
436	dl	1.1	}
437			}