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1.1 |
/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package java.util.concurrent; |
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jsr166 |
1.9 |
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import java.util.ArrayList; |
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1.1 |
import java.util.function.Consumer; |
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import java.util.function.Function; |
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import java.util.stream.Stream; |
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/** |
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* Interrelated interfaces and static methods for establishing |
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* flow-controlled components in which {@link Publisher Publishers} |
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* produce items consumed by one or more {@link Subscriber |
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* Subscribers}, each managed by a {@link Subscription |
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1.14 |
* Subscription}. |
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jsr166 |
1.2 |
* |
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1.1 |
* <p>These interfaces correspond to the <a |
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* href="http://www.reactive-streams.org/"> reactive-streams</a> |
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1.14 |
* specification. They apply in both concurrent and distributed |
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* asynchronous settings: All (seven) methods are defined in {@code |
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* void} "oneway" message style. Communication relies on a simple form |
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* of flow control (method {@link Subscription#request}) that can be |
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* used to avoid resource management problems that may otherwise occur |
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* in "push" based systems. |
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* |
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* <p><b>Examples.</b> A {@link Publisher} usually defines its own |
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* {@link Subscription} implementation; constructing one in method |
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* {@code subscribe} and issuing it to the calling {@link |
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* Subscriber}. It publishes items to the subscriber asynchronously, |
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* normally using an {@link Executor}. For example, here is a very |
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* simple publisher that only issues (when requested) a single {@code |
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1.14 |
* TRUE} item to any subscriber. Because each subscriber receives |
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1.15 |
* only the same single item, this class does not use buffering and |
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* ordering control required in most implementations (for example |
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* {@link SubmissionPublisher}). |
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1.10 |
* |
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* <pre> {@code |
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* class OneShotPublisher implements Publisher<Boolean> { |
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1.15 |
* final Executor executor = ForkJoinPool.commonPool(); // daemon-based |
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1.10 |
* public void subscribe(Subscriber<? super Boolean> subscriber) { |
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1.11 |
* subscriber.onSubscribe(new OneShotSubscription(subscriber, executor)); |
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1.10 |
* } |
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* static class OneShotSubscription implements Subscription { |
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* final Subscriber<? super Boolean> subscriber; |
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* final Executor executor; |
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* boolean completed; |
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* OneShotSubscription(Subscriber<? super Boolean> subscriber, |
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* Executor executor) { |
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* this.subscriber = subscriber; |
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* this.executor = executor; |
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* } |
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* public synchronized void request(long n) { |
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* if (n > 0 && !completed) { |
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* completed = true; |
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* executor.execute(() -> { |
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* subscriber.onNext(Boolean.TRUE); |
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* subscriber.onComplete(); |
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* }); |
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* } |
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* else if (n < 0) { |
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* completed = true; |
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* subscriber.onError(new IllegalArgumentException()); |
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} |
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* } |
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1.15 |
* public synchronized void cancel() { |
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* completed = true; // ineffective if task already started |
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* } |
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1.10 |
* } |
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* }}</pre> |
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* |
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jsr166 |
1.13 |
* <p>A {@link Subscriber} arranges that items be requested and |
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1.10 |
* processed. Items (invocations of {@link Subscriber#onNext}) are |
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* not issued unless requested, but multiple items may be requested. |
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* Many Subscriber implementations can arrange this in the style of |
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* the following example, where a buffer size of 1 single-steps, and |
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* larger sizes usually allow for more efficient overlapped processing |
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* with less communication; for example with a value of 64, this keeps |
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* total outstanding requests between 32 and 64. (See also {@link |
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* #consume(long, Publisher, Consumer)} that automates a common case.) |
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1.14 |
* Because Subscriber method invocations for a given {@link |
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* Subscription} are strictly ordered, there is no need for these |
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* methods to use locks or volatiles unless a Subscriber maintains |
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* multiple Subscriptions (in which case it is better to instead |
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* define multiple Subscribers, each with its own Subscription). |
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1.10 |
* |
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* <pre> {@code |
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* class SampleSubscriber<T> implements Subscriber<T> { |
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* final Consumer<? super T> consumer; |
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* Subscription subscription; |
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* final long bufferSize; |
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* long count; |
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* SampleSubscriber(long bufferSize, Consumer<? super T> consumer) { |
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* this.bufferSize = bufferSize; |
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* this.consumer = consumer; |
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* } |
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* public void onSubscribe(Subscription subscription) { |
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* (this.subscription = subscription).request(bufferSize); |
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* count = bufferSize - bufferSize / 2; // re-request when half consumed |
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* } |
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* public void onNext(T item) { |
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* if (--count <= 0) |
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* subscription.request(count = bufferSize - bufferSize / 2); |
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* consumer.accept(item); |
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* } |
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* public void onError(Throwable ex) { ex.printStackTrace(); } |
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* public void onComplete() {} |
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* }}</pre> |
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1.1 |
* |
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1.14 |
* <p>When flow control is inapplicable, a subscriber may initially |
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1.12 |
* request an effectively unbounded number of items, as in: |
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* |
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* <pre> {@code |
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* class UnboundedSubscriber<T> implements Subscriber<T> { |
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* public void onSubscribe(Subscription subscription) { |
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* subscription.request(Long.MAX_VALUE); // effectively unbounded |
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* } |
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* public void onNext(T item) { use(item); } |
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* public void onError(Throwable ex) { ex.printStackTrace(); } |
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* public void onComplete() {} |
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* void use(T item) { ... } |
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* }}</pre> |
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jsr166 |
1.13 |
* |
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1.1 |
* @author Doug Lea |
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* @since 1.9 |
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*/ |
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public final class Flow { |
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private Flow() {} // uninstantiable |
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/** |
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* A producer of items (and related control messages) received by |
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* Subscribers. Each current {@link Subscriber} receives the same |
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dl |
1.14 |
* items (via method {@code onNext}) in the same order, unless |
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* drops or errors are encountered. If a Publisher encounters an |
139 |
dl |
1.15 |
* error that does not allow items to be issued to a Subscriber, |
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* that Subscriber receives {@code onError}, and then receives no |
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* further messages. Otherwise, when it is known that no further |
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* messages will be issued to it, a subscriber receives {@code |
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* onComplete}. Publishers ensure that Subscriber method |
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dl |
1.14 |
* invocations for each subscription are strictly ordered in <a |
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* href="package-summary.html#MemoryVisibility"><i>happens-before</i></a> |
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* order. |
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* |
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1.15 |
* <p>Publishers may vary in policy about whether drops (failures |
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* to issue an item because of resource limitations) are treated |
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* as unrecoverable errors. Publishers may also vary about |
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* whether Subscribers receive items that were produced or |
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* available before they subscribed. |
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dl |
1.1 |
* |
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* @param <T> the published item type |
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*/ |
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@FunctionalInterface |
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public static interface Publisher<T> { |
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/** |
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* Adds the given Subscriber if possible. If already |
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* subscribed, or the attempt to subscribe fails due to policy |
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dl |
1.14 |
* violations or errors, the Subscriber's {@code onError} |
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* method is invoked with an {@link IllegalStateException}. |
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* Otherwise, the Subscriber's {@code onSubscribe} method is |
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* invoked with a new {@link Subscription}. Subscribers may |
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* enable receiving items by invoking the {@code request} |
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* method of this Subscription, and may unsubscribe by |
167 |
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* invoking its {@code cancel} method. |
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dl |
1.1 |
* |
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* @param subscriber the subscriber |
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* @throws NullPointerException if subscriber is null |
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*/ |
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public void subscribe(Subscriber<? super T> subscriber); |
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} |
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/** |
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dl |
1.14 |
* A receiver of messages. The methods in this interface are |
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* invoked in strict sequential order for each {@link |
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* Subscription}. |
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dl |
1.1 |
* |
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* @param <T> the subscribed item type |
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*/ |
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public static interface Subscriber<T> { |
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/** |
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* Method invoked prior to invoking any other Subscriber |
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* methods for the given Subscription. If this method throws |
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* an exception, resulting behavior is not guaranteed, but may |
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* cause the Subscription to be cancelled. |
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* |
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dl |
1.15 |
* <p>Typically, implementations of this method invoke {@code |
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* subscription.request} to enable receiving items. |
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dl |
1.1 |
* |
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* @param subscription a new subscription |
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*/ |
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public void onSubscribe(Subscription subscription); |
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/** |
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* Method invoked with a Subscription's next item. If this |
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* method throws an exception, resulting behavior is not |
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* guaranteed, but may cause the Subscription to be cancelled. |
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* |
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* @param item the item |
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*/ |
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public void onNext(T item); |
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/** |
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* Method invoked upon an unrecoverable error encountered by a |
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* Publisher or Subscription, after which no other Subscriber |
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* methods are invoked by the Subscription. If this method |
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* itself throws an exception, resulting behavior is |
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* undefined. |
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* |
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* @param throwable the exception |
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*/ |
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public void onError(Throwable throwable); |
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/** |
217 |
dl |
1.15 |
* Method invoked when it is known that no additional |
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* Subscriber method invocations will occur for a Subscription |
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* that is not already terminated by error, after which no |
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* other Subscriber methods are invoked by the Subscription. |
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* If this method throws an exception, resulting behavior is |
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dl |
1.14 |
* undefined. |
223 |
dl |
1.1 |
*/ |
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public void onComplete(); |
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} |
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/** |
228 |
dl |
1.14 |
* Message control linking a {@link Publisher} and {@link |
229 |
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* Subscriber}. Subscribers receive items only when requested, |
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* and may cancel at any time. The methods in this interface are |
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* intended to be invoked only by their Subscribers; usages in |
232 |
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* other contexts have undefined effects. |
233 |
dl |
1.1 |
*/ |
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public static interface Subscription { |
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/** |
236 |
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* Adds the given number {@code n} of items to the current |
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* unfulfilled demand for this subscription. If {@code n} is |
238 |
dl |
1.14 |
* negative, the Subscriber will receive an {@code onError} |
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* signal with an {@link IllegalArgumentException} |
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* argument. Otherwise, the Subscriber will receive up to |
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* {@code n} additional {@code onNext} invocations (or fewer |
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* if terminated). |
243 |
dl |
1.1 |
* |
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* @param n the increment of demand; a value of {@code |
245 |
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* Long.MAX_VALUE} may be considered as effectively unbounded |
246 |
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*/ |
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public void request(long n); |
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249 |
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/** |
250 |
dl |
1.14 |
* Causes the Subscriber to (eventually) stop receiving |
251 |
dl |
1.15 |
* messages. Implementation is best-effort -- additional |
252 |
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* messages may be received after invoking this method. A |
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* cancelled subscription need not ever receive an {@code |
254 |
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* onComplete} signal. |
255 |
dl |
1.1 |
*/ |
256 |
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public void cancel(); |
257 |
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} |
258 |
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259 |
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/** |
260 |
jsr166 |
1.2 |
* A component that acts as both a Subscriber and Publisher. |
261 |
dl |
1.1 |
* |
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jsr166 |
1.2 |
* @param <T> the subscribed item type |
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* @param <R> the published item type |
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*/ |
265 |
jsr166 |
1.5 |
public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> { |
266 |
dl |
1.1 |
} |
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268 |
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// Support for static methods |
269 |
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270 |
dl |
1.10 |
static final long DEFAULT_BUFFER_SIZE = 64L; |
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dl |
1.1 |
|
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jsr166 |
1.3 |
abstract static class CompletableSubscriber<T,U> implements Subscriber<T>, |
273 |
dl |
1.1 |
Consumer<T> { |
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final CompletableFuture<U> status; |
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Subscription subscription; |
276 |
dl |
1.10 |
long requestSize; |
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jsr166 |
1.2 |
long count; |
278 |
dl |
1.10 |
CompletableSubscriber(long bufferSize, CompletableFuture<U> status) { |
279 |
dl |
1.1 |
this.status = status; |
280 |
dl |
1.10 |
this.requestSize = bufferSize; |
281 |
dl |
1.1 |
} |
282 |
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public final void onSubscribe(Subscription subscription) { |
283 |
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(this.subscription = subscription).request(requestSize); |
284 |
dl |
1.10 |
count = requestSize -= (requestSize >>> 1); |
285 |
dl |
1.1 |
} |
286 |
jsr166 |
1.2 |
public final void onError(Throwable ex) { |
287 |
dl |
1.1 |
status.completeExceptionally(ex); |
288 |
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} |
289 |
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public void onNext(T item) { |
290 |
dl |
1.10 |
try { |
291 |
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if (--count <= 0) |
292 |
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subscription.request(count = requestSize); |
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accept(item); |
294 |
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} catch (Throwable ex) { |
295 |
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status.completeExceptionally(ex); |
296 |
dl |
1.1 |
} |
297 |
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} |
298 |
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} |
299 |
jsr166 |
1.2 |
|
300 |
dl |
1.1 |
static final class ConsumeSubscriber<T> extends CompletableSubscriber<T,Void> { |
301 |
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final Consumer<? super T> consumer; |
302 |
dl |
1.10 |
ConsumeSubscriber(long bufferSize, |
303 |
dl |
1.1 |
CompletableFuture<Void> status, |
304 |
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Consumer<? super T> consumer) { |
305 |
dl |
1.10 |
super(bufferSize, status); |
306 |
dl |
1.1 |
this.consumer = consumer; |
307 |
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} |
308 |
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public void accept(T item) { consumer.accept(item); } |
309 |
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public void onComplete() { status.complete(null); } |
310 |
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} |
311 |
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312 |
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/** |
313 |
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* Creates and subscribes a Subscriber that consumes all items |
314 |
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* from the given publisher using the given Consumer function, and |
315 |
dl |
1.10 |
* using the given bufferSize for buffering. Returns a |
316 |
dl |
1.1 |
* CompletableFuture that is completed normally when the publisher |
317 |
dl |
1.14 |
* signals {@code onComplete}, or completed exceptionally upon any |
318 |
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* error, including an exception thrown by the Consumer (in which |
319 |
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* case the subscription is cancelled if not already terminated). |
320 |
dl |
1.1 |
* |
321 |
jsr166 |
1.4 |
* @param <T> the published item type |
322 |
dl |
1.10 |
* @param bufferSize the request size for subscriptions |
323 |
dl |
1.1 |
* @param publisher the publisher |
324 |
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* @param consumer the function applied to each onNext item |
325 |
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* @return a CompletableFuture that is completed normally |
326 |
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* when the publisher signals onComplete, and exceptionally |
327 |
jsr166 |
1.7 |
* upon any error |
328 |
dl |
1.1 |
* @throws NullPointerException if publisher or consumer are null |
329 |
dl |
1.10 |
* @throws IllegalArgumentException if bufferSize not positive |
330 |
dl |
1.1 |
*/ |
331 |
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public static <T> CompletableFuture<Void> consume( |
332 |
dl |
1.10 |
long bufferSize, Publisher<T> publisher, Consumer<? super T> consumer) { |
333 |
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if (bufferSize <= 0L) |
334 |
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throw new IllegalArgumentException("bufferSize must be positive"); |
335 |
dl |
1.1 |
if (publisher == null || consumer == null) |
336 |
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throw new NullPointerException(); |
337 |
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CompletableFuture<Void> status = new CompletableFuture<>(); |
338 |
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publisher.subscribe(new ConsumeSubscriber<T>( |
339 |
dl |
1.10 |
bufferSize, status, consumer)); |
340 |
dl |
1.1 |
return status; |
341 |
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} |
342 |
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|
343 |
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/** |
344 |
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* Equivalent to {@link #consume(long, Publisher, Consumer)} |
345 |
dl |
1.10 |
* with a buffer size of 64. |
346 |
dl |
1.1 |
* |
347 |
jsr166 |
1.4 |
* @param <T> the published item type |
348 |
dl |
1.1 |
* @param publisher the publisher |
349 |
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* @param consumer the function applied to each onNext item |
350 |
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* @return a CompletableFuture that is completed normally |
351 |
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* when the publisher signals onComplete, and exceptionally |
352 |
jsr166 |
1.7 |
* upon any error |
353 |
dl |
1.1 |
* @throws NullPointerException if publisher or consumer are null |
354 |
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*/ |
355 |
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public static <T> CompletableFuture<Void> consume( |
356 |
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Publisher<T> publisher, Consumer<? super T> consumer) { |
357 |
dl |
1.10 |
return consume(DEFAULT_BUFFER_SIZE, publisher, consumer); |
358 |
dl |
1.1 |
} |
359 |
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|
360 |
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/** |
361 |
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* Temporary implementation for Stream, collecting all items |
362 |
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* and then applying stream operation. |
363 |
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*/ |
364 |
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static final class StreamSubscriber<T,R> extends CompletableSubscriber<T,R> { |
365 |
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final Function<? super Stream<T>, ? extends R> fn; |
366 |
|
|
final ArrayList<T> items; |
367 |
dl |
1.10 |
StreamSubscriber(long bufferSize, |
368 |
dl |
1.1 |
CompletableFuture<R> status, |
369 |
|
|
Function<? super Stream<T>, ? extends R> fn) { |
370 |
dl |
1.10 |
super(bufferSize, status); |
371 |
dl |
1.1 |
this.fn = fn; |
372 |
|
|
this.items = new ArrayList<T>(); |
373 |
|
|
} |
374 |
|
|
public void accept(T item) { items.add(item); } |
375 |
|
|
public void onComplete() { status.complete(fn.apply(items.stream())); } |
376 |
|
|
} |
377 |
|
|
|
378 |
|
|
/** |
379 |
|
|
* Creates and subscribes a Subscriber that applies the given |
380 |
dl |
1.10 |
* stream operation to items, and uses the given bufferSize for |
381 |
dl |
1.1 |
* buffering. Returns a CompletableFuture that is completed |
382 |
|
|
* normally with the result of this function when the publisher |
383 |
dl |
1.14 |
* signals {@code onComplete}, or is completed exceptionally upon |
384 |
|
|
* any error. |
385 |
dl |
1.1 |
* |
386 |
|
|
* <p><b>Preliminary release note:</b> Currently, this method |
387 |
|
|
* collects all items before executing the stream |
388 |
|
|
* computation. Improvements are pending Stream integration. |
389 |
|
|
* |
390 |
jsr166 |
1.4 |
* @param <T> the published item type |
391 |
|
|
* @param <R> the result type of the stream function |
392 |
dl |
1.10 |
* @param bufferSize the request size for subscriptions |
393 |
dl |
1.1 |
* @param publisher the publisher |
394 |
|
|
* @param streamFunction the operation on elements |
395 |
|
|
* @return a CompletableFuture that is completed normally with the |
396 |
|
|
* result of the given function as result when the publisher signals |
397 |
jsr166 |
1.7 |
* onComplete, and exceptionally upon any error |
398 |
dl |
1.1 |
* @throws NullPointerException if publisher or function are null |
399 |
dl |
1.10 |
* @throws IllegalArgumentException if bufferSize not positive |
400 |
dl |
1.1 |
*/ |
401 |
|
|
public static <T,R> CompletableFuture<R> stream( |
402 |
dl |
1.10 |
long bufferSize, Publisher<T> publisher, |
403 |
dl |
1.1 |
Function<? super Stream<T>, ? extends R> streamFunction) { |
404 |
dl |
1.10 |
if (bufferSize <= 0L) |
405 |
|
|
throw new IllegalArgumentException("bufferSize must be positive"); |
406 |
dl |
1.1 |
if (publisher == null || streamFunction == null) |
407 |
|
|
throw new NullPointerException(); |
408 |
|
|
CompletableFuture<R> status = new CompletableFuture<>(); |
409 |
|
|
publisher.subscribe(new StreamSubscriber<T,R>( |
410 |
dl |
1.10 |
bufferSize, status, streamFunction)); |
411 |
dl |
1.1 |
return status; |
412 |
|
|
} |
413 |
jsr166 |
1.2 |
|
414 |
dl |
1.1 |
/** |
415 |
|
|
* Equivalent to {@link #stream(long, Publisher, Function)} |
416 |
dl |
1.10 |
* with a buffer size of 64. |
417 |
dl |
1.1 |
* |
418 |
jsr166 |
1.4 |
* @param <T> the published item type |
419 |
|
|
* @param <R> the result type of the stream function |
420 |
dl |
1.1 |
* @param publisher the publisher |
421 |
|
|
* @param streamFunction the operation on elements |
422 |
|
|
* @return a CompletableFuture that is completed normally with the |
423 |
|
|
* result of the given function as result when the publisher signals |
424 |
jsr166 |
1.7 |
* onComplete, and exceptionally upon any error |
425 |
dl |
1.1 |
* @throws NullPointerException if publisher or function are null |
426 |
|
|
*/ |
427 |
|
|
public static <T,R> CompletableFuture<R> stream( |
428 |
jsr166 |
1.2 |
Publisher<T> publisher, |
429 |
dl |
1.1 |
Function<? super Stream<T>,? extends R> streamFunction) { |
430 |
dl |
1.10 |
return stream(DEFAULT_BUFFER_SIZE, publisher, streamFunction); |
431 |
dl |
1.1 |
} |
432 |
|
|
} |