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, executor));
 *   }
 *   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>
 *
 * <p>If there is no chance that a publisher will produce elements
 * faster than they can be consumed, 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 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:	1.13
Committed:	Mon Jan 19 00:49:29 2015 UTC (9 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.12:	+2 -2 lines
Log Message:	whitespace
#	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			* Subscription}. The use of flow control helps address common
20			* resource issues in "push" based asynchronous systems.
21	jsr166	1.2	*
22	dl	1.1	* <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	dl	1.10	* <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	dl	1.11	* subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
43	dl	1.10	* }
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	jsr166	1.13	* <p>A {@link Subscriber} arranges that items be requested and
71	dl	1.10	* 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	dl	1.1	*
103	dl	1.12	* <p>If there is no chance that a publisher will produce elements
104			* faster than they can be consumed, a subscriber may initially
105			* request an effectively unbounded number of items, as in:
106			*
107			* <pre> {@code
108			* class UnboundedSubscriber<T> implements Subscriber<T> {
109			* public void onSubscribe(Subscription subscription) {
110			* subscription.request(Long.MAX_VALUE); // effectively unbounded
111			* }
112			* public void onNext(T item) { use(item); }
113			* public void onError(Throwable ex) { ex.printStackTrace(); }
114			* public void onComplete() {}
115			* void use(T item) { ... }
116			* }}</pre>
117	jsr166	1.13	*
118	dl	1.1	* @author Doug Lea
119			* @since 1.9
120			*/
121			public final class Flow {
122
123			private Flow() {} // uninstantiable
124
125			/**
126			* A producer of items (and related control messages) received by
127			* Subscribers. Each current {@link Subscriber} receives the same
128			* items (via method onNext) in the same order, unless drops or
129			* errors are encountered. If a Publisher encounters an error that
130			* does not allow further items to be issued to a Subscriber, that
131			* Subscriber receives onError, and then receives no further
132			* messages. Otherwise, if it is known that no further items will
133			* be produced, each Subscriber receives onComplete. Publishers
134			* may vary in policy about whether drops (failures to issue an
135			* item because of resource limitations) are treated as errors.
136			* Publishers may also vary about whether Subscribers receive
137			* items that were produced or available before they subscribed.
138			*
139			* @param <T> the published item type
140			*/
141			@FunctionalInterface
142			public static interface Publisher<T> {
143			/**
144			* Adds the given Subscriber if possible. If already
145			* subscribed, or the attempt to subscribe fails due to policy
146			* violations or errors, the Subscriber's onError method is
147			* invoked with an IllegalStateException. Otherwise, upon
148			* success, the Subscriber's onSubscribe method is invoked
149			* with a new Subscription. Subscribers may enable receiving
150			* items by invoking the request method of this Subscription,
151			* and may unsubscribe by invoking its cancel method.
152			*
153			* @param subscriber the subscriber
154			* @throws NullPointerException if subscriber is null
155			*/
156			public void subscribe(Subscriber<? super T> subscriber);
157			}
158
159			/**
160			* A receiver of messages. The methods in this interface must be
161			* invoked sequentially by each Subscription, so are not required
162			* to be thread-safe unless subscribing to multiple publishers.
163			*
164			* @param <T> the subscribed item type
165			*/
166			public static interface Subscriber<T> {
167			/**
168			* Method invoked prior to invoking any other Subscriber
169			* methods for the given Subscription. If this method throws
170			* an exception, resulting behavior is not guaranteed, but may
171			* cause the Subscription to be cancelled.
172			*
173			* <p>Typically, implementations of this method invoke the
174			* subscription's request method to enable receiving items.
175			*
176			* @param subscription a new subscription
177			*/
178			public void onSubscribe(Subscription subscription);
179
180			/**
181			* Method invoked with a Subscription's next item. If this
182			* method throws an exception, resulting behavior is not
183			* guaranteed, but may cause the Subscription to be cancelled.
184			*
185			* @param item the item
186			*/
187			public void onNext(T item);
188
189			/**
190			* Method invoked upon an unrecoverable error encountered by a
191			* Publisher or Subscription, after which no other Subscriber
192			* methods are invoked by the Subscription. If this method
193			* itself throws an exception, resulting behavior is
194			* undefined.
195			*
196			* @param throwable the exception
197			*/
198			public void onError(Throwable throwable);
199
200			/**
201			* Method invoked when it is known that no additional onNext
202			* invocations will occur for a Subscription that is not
203			* already terminated by error, after which no other
204			* Subscriber methods are invoked by the Subscription. If
205			* this method itself throws an exception, resulting behavior
206			* is undefined.
207			*/
208			public void onComplete();
209			}
210
211			/**
212			* Message control linking Publishers and Subscribers.
213			* Subscribers receive items (via onNext) only when requested, and
214			* may cancel at any time. The methods in this interface are
215			* intended to be invoked only by their Subscribers.
216			*/
217			public static interface Subscription {
218			/**
219			* Adds the given number {@code n} of items to the current
220			* unfulfilled demand for this subscription. If {@code n} is
221			* negative, the Subscriber will receive an onError signal
222			* with an IllegalArgumentException argument. Otherwise, the
223			* Subscriber will receive up to {@code n} additional onNext
224	jsr166	1.2	* invocations (or fewer if terminated).
225	dl	1.1	*
226			* @param n the increment of demand; a value of {@code
227			* Long.MAX_VALUE} may be considered as effectively unbounded
228			*/
229			public void request(long n);
230
231			/**
232			* Causes the Subscriber to (eventually) stop receiving onNext
233	jsr166	1.6	* messages.
234	dl	1.1	*/
235			public void cancel();
236			}
237
238			/**
239	jsr166	1.2	* A component that acts as both a Subscriber and Publisher.
240	dl	1.1	*
241	jsr166	1.2	* @param <T> the subscribed item type
242			* @param <R> the published item type
243			*/
244	jsr166	1.5	public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
245	dl	1.1	}
246
247			// Support for static methods
248
249	dl	1.10	static final long DEFAULT_BUFFER_SIZE = 64L;
250	dl	1.1
251	jsr166	1.3	abstract static class CompletableSubscriber<T,U> implements Subscriber<T>,
252	dl	1.1	Consumer<T> {
253			final CompletableFuture<U> status;
254			Subscription subscription;
255	dl	1.10	long requestSize;
256	jsr166	1.2	long count;
257	dl	1.10	CompletableSubscriber(long bufferSize, CompletableFuture<U> status) {
258	dl	1.1	this.status = status;
259	dl	1.10	this.requestSize = bufferSize;
260	dl	1.1	}
261			public final void onSubscribe(Subscription subscription) {
262			(this.subscription = subscription).request(requestSize);
263	dl	1.10	count = requestSize -= (requestSize >>> 1);
264	dl	1.1	}
265	jsr166	1.2	public final void onError(Throwable ex) {
266	dl	1.1	status.completeExceptionally(ex);
267			}
268			public void onNext(T item) {
269	dl	1.10	try {
270			if (--count <= 0)
271			subscription.request(count = requestSize);
272			accept(item);
273			} catch (Throwable ex) {
274			status.completeExceptionally(ex);
275	dl	1.1	}
276			}
277			}
278	jsr166	1.2
279	dl	1.1	static final class ConsumeSubscriber<T> extends CompletableSubscriber<T,Void> {
280			final Consumer<? super T> consumer;
281	dl	1.10	ConsumeSubscriber(long bufferSize,
282	dl	1.1	CompletableFuture<Void> status,
283			Consumer<? super T> consumer) {
284	dl	1.10	super(bufferSize, status);
285	dl	1.1	this.consumer = consumer;
286			}
287			public void accept(T item) { consumer.accept(item); }
288			public void onComplete() { status.complete(null); }
289			}
290
291			/**
292			* Creates and subscribes a Subscriber that consumes all items
293			* from the given publisher using the given Consumer function, and
294	dl	1.10	* using the given bufferSize for buffering. Returns a
295	dl	1.1	* CompletableFuture that is completed normally when the publisher
296			* signals onComplete, or completed exceptionally upon any error,
297			* including an exception thrown by the Consumer (in which case
298			* the subscription is cancelled if not already terminated).
299			*
300	jsr166	1.4	* @param <T> the published item type
301	dl	1.10	* @param bufferSize the request size for subscriptions
302	dl	1.1	* @param publisher the publisher
303			* @param consumer the function applied to each onNext item
304			* @return a CompletableFuture that is completed normally
305			* when the publisher signals onComplete, and exceptionally
306	jsr166	1.7	* upon any error
307	dl	1.1	* @throws NullPointerException if publisher or consumer are null
308	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
309	dl	1.1	*/
310			public static <T> CompletableFuture<Void> consume(
311	dl	1.10	long bufferSize, Publisher<T> publisher, Consumer<? super T> consumer) {
312			if (bufferSize <= 0L)
313			throw new IllegalArgumentException("bufferSize must be positive");
314	dl	1.1	if (publisher == null \|\| consumer == null)
315			throw new NullPointerException();
316			CompletableFuture<Void> status = new CompletableFuture<>();
317			publisher.subscribe(new ConsumeSubscriber<T>(
318	dl	1.10	bufferSize, status, consumer));
319	dl	1.1	return status;
320			}
321
322			/**
323			* Equivalent to {@link #consume(long, Publisher, Consumer)}
324	dl	1.10	* with a buffer size of 64.
325	dl	1.1	*
326	jsr166	1.4	* @param <T> the published item type
327	dl	1.1	* @param publisher the publisher
328			* @param consumer the function applied to each onNext item
329			* @return a CompletableFuture that is completed normally
330			* when the publisher signals onComplete, and exceptionally
331	jsr166	1.7	* upon any error
332	dl	1.1	* @throws NullPointerException if publisher or consumer are null
333			*/
334			public static <T> CompletableFuture<Void> consume(
335			Publisher<T> publisher, Consumer<? super T> consumer) {
336	dl	1.10	return consume(DEFAULT_BUFFER_SIZE, publisher, consumer);
337	dl	1.1	}
338
339			/**
340			* Temporary implementation for Stream, collecting all items
341			* and then applying stream operation.
342			*/
343			static final class StreamSubscriber<T,R> extends CompletableSubscriber<T,R> {
344			final Function<? super Stream<T>, ? extends R> fn;
345			final ArrayList<T> items;
346	dl	1.10	StreamSubscriber(long bufferSize,
347	dl	1.1	CompletableFuture<R> status,
348			Function<? super Stream<T>, ? extends R> fn) {
349	dl	1.10	super(bufferSize, status);
350	dl	1.1	this.fn = fn;
351			this.items = new ArrayList<T>();
352			}
353			public void accept(T item) { items.add(item); }
354			public void onComplete() { status.complete(fn.apply(items.stream())); }
355			}
356
357			/**
358			* Creates and subscribes a Subscriber that applies the given
359	dl	1.10	* stream operation to items, and uses the given bufferSize for
360	dl	1.1	* buffering. Returns a CompletableFuture that is completed
361			* normally with the result of this function when the publisher
362			* signals onComplete, or is completed exceptionally upon any
363			* error.
364			*
365			* <p><b>Preliminary release note:</b> Currently, this method
366			* collects all items before executing the stream
367			* computation. Improvements are pending Stream integration.
368			*
369	jsr166	1.4	* @param <T> the published item type
370			* @param <R> the result type of the stream function
371	dl	1.10	* @param bufferSize the request size for subscriptions
372	dl	1.1	* @param publisher the publisher
373			* @param streamFunction the operation on elements
374			* @return a CompletableFuture that is completed normally with the
375			* result of the given function as result when the publisher signals
376	jsr166	1.7	* onComplete, and exceptionally upon any error
377	dl	1.1	* @throws NullPointerException if publisher or function are null
378	dl	1.10	* @throws IllegalArgumentException if bufferSize not positive
379	dl	1.1	*/
380			public static <T,R> CompletableFuture<R> stream(
381	dl	1.10	long bufferSize, Publisher<T> publisher,
382	dl	1.1	Function<? super Stream<T>, ? extends R> streamFunction) {
383	dl	1.10	if (bufferSize <= 0L)
384			throw new IllegalArgumentException("bufferSize must be positive");
385	dl	1.1	if (publisher == null \|\| streamFunction == null)
386			throw new NullPointerException();
387			CompletableFuture<R> status = new CompletableFuture<>();
388			publisher.subscribe(new StreamSubscriber<T,R>(
389	dl	1.10	bufferSize, status, streamFunction));
390	dl	1.1	return status;
391			}
392	jsr166	1.2
393	dl	1.1	/**
394			* Equivalent to {@link #stream(long, Publisher, Function)}
395	dl	1.10	* with a buffer size of 64.
396	dl	1.1	*
397	jsr166	1.4	* @param <T> the published item type
398			* @param <R> the result type of the stream function
399	dl	1.1	* @param publisher the publisher
400			* @param streamFunction the operation on elements
401			* @return a CompletableFuture that is completed normally with the
402			* result of the given function as result when the publisher signals
403	jsr166	1.7	* onComplete, and exceptionally upon any error
404	dl	1.1	* @throws NullPointerException if publisher or function are null
405			*/
406			public static <T,R> CompletableFuture<R> stream(
407	jsr166	1.2	Publisher<T> publisher,
408	dl	1.1	Function<? super Stream<T>,? extends R> streamFunction) {
409	dl	1.10	return stream(DEFAULT_BUFFER_SIZE, publisher, streamFunction);
410	dl	1.1	}
411	dl	1.10
412	dl	1.1	}