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 ExecutorService 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 ExecutorService executor;
 *     Future<?> future; // to allow cancellation
 *     boolean completed = false;
 *     OneShotSubscription(Subscriber<? super Boolean> subscriber,
 *                         ExecutorService executor) {
 *       this.subscriber = subscriber;
 *       this.executor = executor;
 *     }
 *     public synchronized void request(long n) {
 *       if (n != 0 && !completed) {
 *         completed = true;
 *         future = executor.submit(() -> {
 *           if (n < 0)
 *             subscriber.onError(new IllegalArgumentException());
 *           else {
 *             subscriber.onNext(Boolean.TRUE);
 *             subscriber.onComplete();
 *           }});
 *       }
 *     }
 *     public synchronized void cancel() {
 *       completed = true;
 *       if (future != null) future.cancel(false);
 *     }
 *   }
 * }}</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:	1.17
Committed:	Mon Jan 19 18:15:09 2015 UTC (9 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.16:	+7 -5 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	1.17	* final ExecutorService 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	dl	1.17	* final ExecutorService executor;
56			* Future<?> future; // to allow cancellation
57	dl	1.16	* boolean completed = false;
58	dl	1.10	* OneShotSubscription(Subscriber<? super Boolean> subscriber,
59	dl	1.17	* ExecutorService executor) {
60	dl	1.10	* this.subscriber = subscriber;
61			* this.executor = executor;
62			* }
63			* public synchronized void request(long n) {
64	dl	1.16	* if (n != 0 && !completed) {
65	dl	1.10	* completed = true;
66	dl	1.17	* future = executor.submit(() -> {
67	dl	1.16	* if (n < 0)
68			* subscriber.onError(new IllegalArgumentException());
69			* else {
70			* subscriber.onNext(Boolean.TRUE);
71			* subscriber.onComplete();
72			* }});
73	dl	1.10	* }
74			* }
75	dl	1.15	* public synchronized void cancel() {
76	dl	1.17	* completed = true;
77			* if (future != null) future.cancel(false);
78	dl	1.15	* }
79	dl	1.10	* }
80			* }}</pre>
81			*
82	jsr166	1.13	* <p>A {@link Subscriber} arranges that items be requested and
83	dl	1.10	* processed. Items (invocations of {@link Subscriber#onNext}) are
84			* not issued unless requested, but multiple items may be requested.
85			* Many Subscriber implementations can arrange this in the style of
86			* the following example, where a buffer size of 1 single-steps, and
87			* larger sizes usually allow for more efficient overlapped processing
88			* with less communication; for example with a value of 64, this keeps
89			* total outstanding requests between 32 and 64. (See also {@link
90			* #consume(long, Publisher, Consumer)} that automates a common case.)
91	dl	1.14	* Because Subscriber method invocations for a given {@link
92			* Subscription} are strictly ordered, there is no need for these
93			* methods to use locks or volatiles unless a Subscriber maintains
94			* multiple Subscriptions (in which case it is better to instead
95			* define multiple Subscribers, each with its own Subscription).
96	dl	1.10	*
97			* <pre> {@code
98			* class SampleSubscriber<T> implements Subscriber<T> {
99			* final Consumer<? super T> consumer;
100			* Subscription subscription;
101			* final long bufferSize;
102			* long count;
103			* SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
104			* this.bufferSize = bufferSize;
105			* this.consumer = consumer;
106			* }
107			* public void onSubscribe(Subscription subscription) {
108			* (this.subscription = subscription).request(bufferSize);
109			* count = bufferSize - bufferSize / 2; // re-request when half consumed
110			* }
111			* public void onNext(T item) {
112			* if (--count <= 0)
113			* subscription.request(count = bufferSize - bufferSize / 2);
114			* consumer.accept(item);
115			* }
116			* public void onError(Throwable ex) { ex.printStackTrace(); }
117			* public void onComplete() {}
118			* }}</pre>
119	dl	1.1	*
120	dl	1.14	* <p>When flow control is inapplicable, a subscriber may initially
121	dl	1.12	* request an effectively unbounded number of items, as in:
122			*
123			* <pre> {@code
124			* class UnboundedSubscriber<T> implements Subscriber<T> {
125			* public void onSubscribe(Subscription subscription) {
126			* subscription.request(Long.MAX_VALUE); // effectively unbounded
127			* }
128			* public void onNext(T item) { use(item); }
129			* public void onError(Throwable ex) { ex.printStackTrace(); }
130			* public void onComplete() {}
131			* void use(T item) { ... }
132			* }}</pre>
133	jsr166	1.13	*
134	dl	1.1	* @author Doug Lea
135			* @since 1.9
136			*/
137			public final class Flow {
138
139			private Flow() {} // uninstantiable
140
141			/**
142			* A producer of items (and related control messages) received by
143			* Subscribers. Each current {@link Subscriber} receives the same
144	dl	1.14	* items (via method {@code onNext}) in the same order, unless
145			* drops or errors are encountered. If a Publisher encounters an
146	dl	1.15	* error that does not allow items to be issued to a Subscriber,
147			* that Subscriber receives {@code onError}, and then receives no
148			* further messages. Otherwise, when it is known that no further
149			* messages will be issued to it, a subscriber receives {@code
150			* onComplete}. Publishers ensure that Subscriber method
151	dl	1.14	* invocations for each subscription are strictly ordered in <a
152			* href="package-summary.html#MemoryVisibility"><i>happens-before</i></a>
153			* order.
154			*
155	dl	1.15	* <p>Publishers may vary in policy about whether drops (failures
156			* to issue an item because of resource limitations) are treated
157			* as unrecoverable errors. Publishers may also vary about
158			* whether Subscribers receive items that were produced or
159			* available before they subscribed.
160	dl	1.1	*
161			* @param <T> the published item type
162			*/
163			@FunctionalInterface
164			public static interface Publisher<T> {
165			/**
166			* Adds the given Subscriber if possible. If already
167			* subscribed, or the attempt to subscribe fails due to policy
168	dl	1.14	* violations or errors, the Subscriber's {@code onError}
169			* method is invoked with an {@link IllegalStateException}.
170			* Otherwise, the Subscriber's {@code onSubscribe} method is
171			* invoked with a new {@link Subscription}. Subscribers may
172			* enable receiving items by invoking the {@code request}
173			* method of this Subscription, and may unsubscribe by
174			* invoking its {@code cancel} method.
175	dl	1.1	*
176			* @param subscriber the subscriber
177			* @throws NullPointerException if subscriber is null
178			*/
179			public void subscribe(Subscriber<? super T> subscriber);
180			}
181
182			/**
183	dl	1.14	* A receiver of messages. The methods in this interface are
184			* invoked in strict sequential order for each {@link
185			* Subscription}.
186	dl	1.1	*
187			* @param <T> the subscribed item type
188			*/
189			public static interface Subscriber<T> {
190			/**
191			* Method invoked prior to invoking any other Subscriber
192			* methods for the given Subscription. If this method throws
193			* an exception, resulting behavior is not guaranteed, but may
194			* cause the Subscription to be cancelled.
195			*
196	dl	1.15	* <p>Typically, implementations of this method invoke {@code
197			* subscription.request} to enable receiving items.
198	dl	1.1	*
199			* @param subscription a new subscription
200			*/
201			public void onSubscribe(Subscription subscription);
202
203			/**
204			* Method invoked with a Subscription's next item. If this
205			* method throws an exception, resulting behavior is not
206			* guaranteed, but may cause the Subscription to be cancelled.
207			*
208			* @param item the item
209			*/
210			public void onNext(T item);
211
212			/**
213			* Method invoked upon an unrecoverable error encountered by a
214			* Publisher or Subscription, after which no other Subscriber
215			* methods are invoked by the Subscription. If this method
216			* itself throws an exception, resulting behavior is
217			* undefined.
218			*
219			* @param throwable the exception
220			*/
221			public void onError(Throwable throwable);
222
223			/**
224	dl	1.15	* Method invoked when it is known that no additional
225			* Subscriber method invocations will occur for a Subscription
226			* that is not already terminated by error, after which no
227			* other Subscriber methods are invoked by the Subscription.
228			* If this method throws an exception, resulting behavior is
229	dl	1.14	* undefined.
230	dl	1.1	*/
231			public void onComplete();
232			}
233
234			/**
235	dl	1.14	* Message control linking a {@link Publisher} and {@link
236			* Subscriber}. Subscribers receive items only when requested,
237			* and may cancel at any time. The methods in this interface are
238			* intended to be invoked only by their Subscribers; usages in
239			* other contexts have undefined effects.
240	dl	1.1	*/
241			public static interface Subscription {
242			/**
243			* Adds the given number {@code n} of items to the current
244			* unfulfilled demand for this subscription. If {@code n} is
245	dl	1.14	* negative, the Subscriber will receive an {@code onError}
246			* signal with an {@link IllegalArgumentException}
247			* argument. Otherwise, the Subscriber will receive up to
248			* {@code n} additional {@code onNext} invocations (or fewer
249			* if terminated).
250	dl	1.1	*
251			* @param n the increment of demand; a value of {@code
252			* Long.MAX_VALUE} may be considered as effectively unbounded
253			*/
254			public void request(long n);
255
256			/**
257	dl	1.14	* Causes the Subscriber to (eventually) stop receiving
258	dl	1.15	* messages. Implementation is best-effort -- additional
259			* messages may be received after invoking this method. A
260			* cancelled subscription need not ever receive an {@code
261			* onComplete} signal.
262	dl	1.1	*/
263			public void cancel();
264			}
265
266			/**
267	jsr166	1.2	* A component that acts as both a Subscriber and Publisher.
268	dl	1.1	*
269	jsr166	1.2	* @param <T> the subscribed item type
270			* @param <R> the published item type
271			*/
272	jsr166	1.5	public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
273	dl	1.1	}
274
275			// Support for static methods
276
277	dl	1.10	static final long DEFAULT_BUFFER_SIZE = 64L;
278	dl	1.1
279	jsr166	1.3	abstract static class CompletableSubscriber<T,U> implements Subscriber<T>,
280	dl	1.1	Consumer<T> {
281			final CompletableFuture<U> status;
282			Subscription subscription;
283	dl	1.10	long requestSize;
284	jsr166	1.2	long count;
285	dl	1.10	CompletableSubscriber(long bufferSize, CompletableFuture<U> status) {
286	dl	1.1	this.status = status;
287	dl	1.10	this.requestSize = bufferSize;
288	dl	1.1	}
289			public final void onSubscribe(Subscription subscription) {
290			(this.subscription = subscription).request(requestSize);
291	dl	1.10	count = requestSize -= (requestSize >>> 1);
292	dl	1.1	}
293	jsr166	1.2	public final void onError(Throwable ex) {
294	dl	1.1	status.completeExceptionally(ex);
295			}
296			public void onNext(T item) {
297	dl	1.10	try {
298			if (--count <= 0)
299			subscription.request(count = requestSize);
300			accept(item);
301			} catch (Throwable ex) {
302			status.completeExceptionally(ex);
303	dl	1.1	}
304			}
305			}
306	jsr166	1.2
307	dl	1.1	static final class ConsumeSubscriber<T> extends CompletableSubscriber<T,Void> {
308			final Consumer<? super T> consumer;
309	dl	1.10	ConsumeSubscriber(long bufferSize,
310	dl	1.1	CompletableFuture<Void> status,
311			Consumer<? super T> consumer) {
312	dl	1.10	super(bufferSize, status);
313	dl	1.1	this.consumer = consumer;
314			}
315			public void accept(T item) { consumer.accept(item); }
316			public void onComplete() { status.complete(null); }
317			}
318
319			/**
320			* Creates and subscribes a Subscriber that consumes all items
321			* from the given publisher using the given Consumer function, and
322	dl	1.10	* using the given bufferSize for buffering. Returns a
323	dl	1.1	* CompletableFuture that is completed normally when the publisher
324	dl	1.14	* signals {@code onComplete}, or completed exceptionally upon any
325			* error, including an exception thrown by the Consumer (in which
326			* case the subscription is cancelled if not already terminated).
327	dl	1.1	*
328	jsr166	1.4	* @param <T> the published item type
329	dl	1.10	* @param bufferSize the request size for subscriptions
330	dl	1.1	* @param publisher the publisher
331			* @param consumer the function applied to each onNext item
332			* @return a CompletableFuture that is completed normally
333			* when the publisher signals onComplete, and exceptionally
334	jsr166	1.7	* upon any error
335	dl	1.1	* @throws NullPointerException if publisher or consumer are null
336	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
337	dl	1.1	*/
338			public static <T> CompletableFuture<Void> consume(
339	dl	1.10	long bufferSize, Publisher<T> publisher, Consumer<? super T> consumer) {
340			if (bufferSize <= 0L)
341			throw new IllegalArgumentException("bufferSize must be positive");
342	dl	1.1	if (publisher == null \|\| consumer == null)
343			throw new NullPointerException();
344			CompletableFuture<Void> status = new CompletableFuture<>();
345			publisher.subscribe(new ConsumeSubscriber<T>(
346	dl	1.10	bufferSize, status, consumer));
347	dl	1.1	return status;
348			}
349
350			/**
351			* Equivalent to {@link #consume(long, Publisher, Consumer)}
352	dl	1.10	* with a buffer size of 64.
353	dl	1.1	*
354	jsr166	1.4	* @param <T> the published item type
355	dl	1.1	* @param publisher the publisher
356			* @param consumer the function applied to each onNext item
357			* @return a CompletableFuture that is completed normally
358			* when the publisher signals onComplete, and exceptionally
359	jsr166	1.7	* upon any error
360	dl	1.1	* @throws NullPointerException if publisher or consumer are null
361			*/
362			public static <T> CompletableFuture<Void> consume(
363			Publisher<T> publisher, Consumer<? super T> consumer) {
364	dl	1.10	return consume(DEFAULT_BUFFER_SIZE, publisher, consumer);
365	dl	1.1	}
366
367			/**
368			* Temporary implementation for Stream, collecting all items
369			* and then applying stream operation.
370			*/
371			static final class StreamSubscriber<T,R> extends CompletableSubscriber<T,R> {
372			final Function<? super Stream<T>, ? extends R> fn;
373			final ArrayList<T> items;
374	dl	1.10	StreamSubscriber(long bufferSize,
375	dl	1.1	CompletableFuture<R> status,
376			Function<? super Stream<T>, ? extends R> fn) {
377	dl	1.10	super(bufferSize, status);
378	dl	1.1	this.fn = fn;
379			this.items = new ArrayList<T>();
380			}
381			public void accept(T item) { items.add(item); }
382			public void onComplete() { status.complete(fn.apply(items.stream())); }
383			}
384
385			/**
386			* Creates and subscribes a Subscriber that applies the given
387	dl	1.10	* stream operation to items, and uses the given bufferSize for
388	dl	1.1	* buffering. Returns a CompletableFuture that is completed
389			* normally with the result of this function when the publisher
390	dl	1.14	* signals {@code onComplete}, or is completed exceptionally upon
391			* any error.
392	dl	1.1	*
393			* <p><b>Preliminary release note:</b> Currently, this method
394			* collects all items before executing the stream
395			* computation. Improvements are pending Stream integration.
396			*
397	jsr166	1.4	* @param <T> the published item type
398			* @param <R> the result type of the stream function
399	dl	1.10	* @param bufferSize the request size for subscriptions
400	dl	1.1	* @param publisher the publisher
401			* @param streamFunction the operation on elements
402			* @return a CompletableFuture that is completed normally with the
403			* result of the given function as result when the publisher signals
404	jsr166	1.7	* onComplete, and exceptionally upon any error
405	dl	1.1	* @throws NullPointerException if publisher or function are null
406	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
407	dl	1.1	*/
408			public static <T,R> CompletableFuture<R> stream(
409	dl	1.10	long bufferSize, Publisher<T> publisher,
410	dl	1.1	Function<? super Stream<T>, ? extends R> streamFunction) {
411	dl	1.10	if (bufferSize <= 0L)
412			throw new IllegalArgumentException("bufferSize must be positive");
413	dl	1.1	if (publisher == null \|\| streamFunction == null)
414			throw new NullPointerException();
415			CompletableFuture<R> status = new CompletableFuture<>();
416			publisher.subscribe(new StreamSubscriber<T,R>(
417	dl	1.10	bufferSize, status, streamFunction));
418	dl	1.1	return status;
419			}
420	jsr166	1.2
421	dl	1.1	/**
422			* Equivalent to {@link #stream(long, Publisher, Function)}
423	dl	1.10	* with a buffer size of 64.
424	dl	1.1	*
425	jsr166	1.4	* @param <T> the published item type
426			* @param <R> the result type of the stream function
427	dl	1.1	* @param publisher the publisher
428			* @param streamFunction the operation on elements
429			* @return a CompletableFuture that is completed normally with the
430			* result of the given function as result when the publisher signals
431	jsr166	1.7	* onComplete, and exceptionally upon any error
432	dl	1.1	* @throws NullPointerException if publisher or function are null
433			*/
434			public static <T,R> CompletableFuture<R> stream(
435	jsr166	1.2	Publisher<T> publisher,
436	dl	1.1	Function<? super Stream<T>,? extends R> streamFunction) {
437	dl	1.10	return stream(DEFAULT_BUFFER_SIZE, publisher, streamFunction);
438	dl	1.1	}
439			}