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}. The use of flow control helps address common
 * resource issues in "push" based asynchronous systems.
 *
 * <p>These interfaces correspond to the <a
 * href="http://www.reactive-streams.org/"> reactive-streams</a>
 * specification. (<b>Preliminary release note:</b> This spec is
 * not yet finalized, so minor details could change.)
 *
 * <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 each subscriber, then completes.  Because each
 * subscriber receives only the same single item, this class does not
 * need the buffering and ordering control required in most
 * implementations.
 *
 * <pre> {@code
 * class OneShotPublisher implements Publisher<Boolean> {
 *   final Executor executor = Executors.newSingleThreadExecutor();
 *   public void subscribe(Subscriber<? super Boolean> subscriber) {
 *       subscriber.onSubscribe(new OneShotSubscription(subscriber));
 *   }
 *   static class OneShotSubscription implements Subscription {
 *     final Subscriber<? super Boolean> subscriber;
 *     final Executor executor;
 *     boolean completed;
 *     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(() -> {
 *                   subscriber.onNext(Boolean.TRUE);
 *                   subscriber.onComplete();
 *               });
 *       }
 *       else if (n < 0) {
 *         completed = true;
 *         subscriber.onError(new IllegalArgumentException());
         }
 *     }
 *     public synchronized void cancel() { completed = true; }
 *   }
 * }}</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.)
 *
 * <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>
 *
 * @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 onNext) in the same order, unless drops or
     * errors are encountered. If a Publisher encounters an error that
     * does not allow further items to be issued to a Subscriber, that
     * Subscriber receives onError, and then receives no further
     * messages.  Otherwise, if it is known that no further items will
     * be produced, each Subscriber receives onComplete.  Publishers
     * may vary in policy about whether drops (failures to issue an
     * item because of resource limitations) are treated as 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 onError method is
         * invoked with an IllegalStateException.  Otherwise, upon
         * success, the Subscriber's onSubscribe method is invoked
         * with a new Subscription.  Subscribers may enable receiving
         * items by invoking the request method of this Subscription,
         * and may unsubscribe by invoking its 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 must be
     * invoked sequentially by each Subscription, so are not required
     * to be thread-safe unless subscribing to multiple publishers.
     *
     * @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 the
         * subscription's request method 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 onNext
         * 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 itself throws an exception, resulting behavior
         * is undefined.
         */
        public void onComplete();
    }

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