content: /*
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * 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;
  
  // Android-changed: Remove reference to SubmissionPublisher class (not present on Android).
  /**
   * Interrelated interfaces and static methods for establishing
   * flow-controlled components in which {@link Publisher Publishers}
   * produce items consumed by one or more {@link Subscriber
   * Subscribers}, each managed by a {@link Subscription
   * Subscription}.
   *
   * <p>These interfaces correspond to the <a
   * href="http://www.reactive-streams.org/"> reactive-streams</a>
   * specification.  They apply in both concurrent and distributed
   * asynchronous settings: All (seven) methods are defined in {@code
   * void} "one-way" message style. Communication relies on a simple form
   * of flow control (method {@link Subscription#request}) that can be
   * used to avoid resource management problems that may otherwise occur
   * in "push" based systems.
   *
   * <p><b>Examples.</b> A {@link Publisher} usually defines its own
   * {@link Subscription} implementation; constructing one in method
   * {@code subscribe} and issuing it to the calling {@link
   * Subscriber}. It publishes items to the subscriber asynchronously,
   * normally using an {@link Executor}.  For example, here is a very
   * simple publisher that only issues (when requested) a single {@code
   * TRUE} item to a single subscriber.  Because the subscriber receives
   * only a single item, this class does not use buffering and ordering
   * control required in most implementations.
   *
   * <pre> {@code
   * class OneShotPublisher implements Publisher<Boolean> {
   *   private final ExecutorService executor = ForkJoinPool.commonPool(); // daemon-based
   *   private boolean subscribed; // true after first subscribe
   *   public synchronized void subscribe(Subscriber<? super Boolean> subscriber) {
   *     if (subscribed)
   *       subscriber.onError(new IllegalStateException()); // only one allowed
   *     else {
   *       subscribed = true;
   *       subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
   *     }
   *   }
   *   static class OneShotSubscription implements Subscription {
   *     private final Subscriber<? super Boolean> subscriber;
   *     private final ExecutorService executor;
   *     private Future<?> future; // to allow cancellation
   *     private boolean completed;
   *     OneShotSubscription(Subscriber<? super Boolean> subscriber,
   *                         ExecutorService executor) {
   *       this.subscriber = subscriber;
   *       this.executor = executor;
   *     }
   *     public synchronized void request(long n) {
   *       if (n != 0 && !completed) {
   *         completed = true;
   *         if (n < 0) {
   *           IllegalArgumentException ex = new IllegalArgumentException();
   *           executor.execute(() -> subscriber.onError(ex));
   *         } else {
   *           future = executor.submit(() -> {
   *             subscriber.onNext(Boolean.TRUE);
   *             subscriber.onComplete();
   *           });
   *         }
   *       }
   *     }
   *     public synchronized void cancel() {
   *       completed = true;
   *       if (future != null) future.cancel(false);
   *     }
   *   }
   * }}</pre>
   *
   * <p>A {@link Subscriber} arranges that items be requested and
   * processed.  Items (invocations of {@link Subscriber#onNext}) are
   * not issued unless requested, but multiple items may be requested.
   * Many Subscriber implementations can arrange this in the style of
   * the following example, where a buffer size of 1 single-steps, and
   * larger sizes usually allow for more efficient overlapped processing
   * with less communication; for example with a value of 64, this keeps
   * total outstanding requests between 32 and 64.
   * Because Subscriber method invocations for a given {@link
   * Subscription} are strictly ordered, there is no need for these
   * methods to use locks or volatiles unless a Subscriber maintains
   * multiple Subscriptions (in which case it is better to instead
   * define multiple Subscribers, each with its own Subscription).
   *
   * <pre> {@code
   * class SampleSubscriber<T> implements Subscriber<T> {
   *   final Consumer<? super T> consumer;
   *   Subscription subscription;
   *   final long bufferSize;
   *   long count;
   *   SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
   *     this.bufferSize = bufferSize;
   *     this.consumer = consumer;
   *   }
   *   public void onSubscribe(Subscription subscription) {
   *     long initialRequestSize = bufferSize;
   *     count = bufferSize - bufferSize / 2; // re-request when half consumed
   *     (this.subscription = subscription).request(initialRequestSize);
   *   }
   *   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>The default value of {@link #defaultBufferSize} may provide a
   * useful starting point for choosing request sizes and capacities in
   * Flow components based on expected rates, resources, and usages.
   * Or, when flow control is never needed, 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 9
   */
  public final class Flow {
  
      private Flow() {} // uninstantiable
  
      /**
       * A producer of items (and related control messages) received by
       * Subscribers.  Each current {@link Subscriber} receives the same
       * items (via method {@code onNext}) in the same order, unless
       * drops or errors are encountered. If a Publisher encounters an
       * error that does not allow items to be issued to a Subscriber,
       * that Subscriber receives {@code onError}, and then receives no
       * further messages.  Otherwise, when it is known that no further
       * messages will be issued to it, a subscriber receives {@code
       * onComplete}.  Publishers ensure that Subscriber method
       * invocations for each subscription are strictly ordered in <a
       * href="package-summary.html#MemoryVisibility"><i>happens-before</i></a>
       * order.
       *
       * <p>Publishers may vary in policy about whether drops (failures
       * to issue an item because of resource limitations) are treated
       * as unrecoverable errors.  Publishers may also vary about
       * whether Subscribers receive items that were produced or
       * available before they subscribed.
       *
       * @param <T> the published item type
       */
      @FunctionalInterface
      public static interface Publisher<T> {
          /**
           * Adds the given Subscriber if possible.  If already
           * subscribed, or the attempt to subscribe fails due to policy
           * violations or errors, the Subscriber's {@code onError}
           * method is invoked with an {@link IllegalStateException}.
           * Otherwise, the Subscriber's {@code onSubscribe} method is
           * invoked with a new {@link Subscription}.  Subscribers may
           * enable receiving items by invoking the {@code request}
           * method of this Subscription, and may unsubscribe by
           * invoking its {@code cancel} method.
           *
           * @param subscriber the subscriber
           * @throws NullPointerException if subscriber is null
           */
          public void subscribe(Subscriber<? super T> subscriber);
      }
  
      /**
       * A receiver of messages.  The methods in this interface are
       * invoked in strict sequential order for each {@link
       * Subscription}.
       *
       * @param <T> the subscribed item type
       */
      public static interface Subscriber<T> {
          /**
           * Method invoked prior to invoking any other Subscriber
           * methods for the given Subscription. If this method throws
           * an exception, resulting behavior is not guaranteed, but may
           * cause the Subscription not to be established or to be cancelled.
           *
           * <p>Typically, implementations of this method invoke {@code
           * subscription.request} to enable receiving items.
           *
           * @param subscription a new subscription
           */
          public void onSubscribe(Subscription subscription);
  
          /**
           * Method invoked with a Subscription's next item.  If this
           * method throws an exception, resulting behavior is not
           * guaranteed, but may cause the Subscription to be cancelled.
           *
           * @param item the item
           */
          public void onNext(T item);
  
          /**
           * Method invoked upon an unrecoverable error encountered by a
           * Publisher or Subscription, after which no other Subscriber
           * methods are invoked by the Subscription.  If this method
           * itself throws an exception, resulting behavior is
           * undefined.
           *
           * @param throwable the exception
           */
          public void onError(Throwable throwable);
  
          /**
           * Method invoked when it is known that no additional
           * Subscriber method invocations will occur for a Subscription
           * that is not already terminated by error, after which no
           * other Subscriber methods are invoked by the Subscription.
           * If this method throws an exception, resulting behavior is
           * undefined.
           */
          public void onComplete();
      }
  
      /**
       * Message control linking a {@link Publisher} and {@link
       * Subscriber}.  Subscribers receive items only when requested,
       * and may cancel at any time. The methods in this interface are
       * intended to be invoked only by their Subscribers; usages in
       * other contexts have undefined effects.
       */
      public static interface Subscription {
          /**
           * Adds the given number {@code n} of items to the current
           * unfulfilled demand for this subscription.  If {@code n} is
           * less than or equal to zero, the Subscriber will receive an
           * {@code onError} signal with an {@link
           * IllegalArgumentException} argument.  Otherwise, the
           * Subscriber will receive up to {@code n} additional {@code
           * onNext} invocations (or fewer if terminated).
           *
           * @param n the increment of demand; a value of {@code
           * Long.MAX_VALUE} may be considered as effectively unbounded
           */
          public void request(long n);
  
          /**
           * Causes the Subscriber to (eventually) stop receiving
           * messages.  Implementation is best-effort -- additional
           * messages may be received after invoking this method.
           * A cancelled subscription need not ever receive an
           * {@code onComplete} or {@code onError} signal.
           */
          public void cancel();
      }
  
      /**
       * A component that acts as both a Subscriber and Publisher.
       *
       * @param <T> the subscribed item type
       * @param <R> the published item type
       */
      public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
      }
  
      static final int DEFAULT_BUFFER_SIZE = 256;
  
      /**
       * Returns a default value for Publisher or Subscriber buffering,
       * that may be used in the absence of other constraints.
       *
       * @implNote
       * The current value returned is 256.
       *
       * @return the buffer size value
       */
      public static int defaultBufferSize() {
          return DEFAULT_BUFFER_SIZE;
      }
  
  }
  