test/jdk/java/net/httpclient/reactivestreams-tck/org/reactivestreams/example/unicast/AsyncSubscriber.java - platform/libcore - Git at Google

 /*
  * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
  * 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.
  *
  * 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.
  */

 package org.reactivestreams.example.unicast;

 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;

 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.ConcurrentLinkedQueue;

 /**
  * AsyncSubscriber is an implementation of Reactive Streams `Subscriber`,
  * it runs asynchronously (on an Executor), requests one element
  * at a time, and invokes a user-defined method to process each element.
  *
  * NOTE: The code below uses a lot of try-catches to show the reader where exceptions can be expected, and where they are forbidden.
  */
 public abstract class AsyncSubscriber<T> implements Subscriber<T>, Runnable {

   // Signal represents the asynchronous protocol between the Publisher and Subscriber
   private static interface Signal {}

   private enum OnComplete implements Signal { Instance; }

   private static class OnError implements Signal {
     public final Throwable error;
     public OnError(final Throwable error) { this.error = error; }
   }

   private static class OnNext<T> implements Signal {
     public final T next;
     public OnNext(final T next) { this.next = next; }
   }

   private static class OnSubscribe implements Signal {
     public final Subscription subscription;
     public OnSubscribe(final Subscription subscription) { this.subscription = subscription; }
   }

   private Subscription subscription; // Obeying rule 3.1, we make this private!
   private boolean done; // It's useful to keep track of whether this Subscriber is done or not
   private final Executor executor; // This is the Executor we'll use to be asynchronous, obeying rule 2.2

   // Only one constructor, and it's only accessible for the subclasses
   protected AsyncSubscriber(Executor executor) {
     if (executor == null) throw null;
     this.executor = executor;
   }

   // Showcases a convenience method to idempotently marking the Subscriber as "done", so we don't want to process more elements
   // herefor we also need to cancel our `Subscription`.
   private final void done() {
     //On this line we could add a guard against `!done`, but since rule 3.7 says that `Subscription.cancel()` is idempotent, we don't need to.
     done = true; // If `whenNext` throws an exception, let's consider ourselves done (not accepting more elements)
     if (subscription != null) { // If we are bailing out before we got a `Subscription` there's little need for cancelling it.
       try {
         subscription.cancel(); // Cancel the subscription
       } catch(final Throwable t) {
         //Subscription.cancel is not allowed to throw an exception, according to rule 3.15
         (new IllegalStateException(subscription + " violated the Reactive Streams rule 3.15 by throwing an exception from cancel.", t)).printStackTrace(System.err);
       }
     }
   }

   // This method is invoked when the OnNext signals arrive
   // Returns whether more elements are desired or not, and if no more elements are desired,
   // for convenience.
   protected abstract boolean whenNext(final T element);

   // This method is invoked when the OnComplete signal arrives
   // override this method to implement your own custom onComplete logic.
   protected void whenComplete() { }

   // This method is invoked if the OnError signal arrives
   // override this method to implement your own custom onError logic.
   protected void whenError(Throwable error) { }

   private final void handleOnSubscribe(final Subscription s) {
     if (s == null) {
       // Getting a null `Subscription` here is not valid so lets just ignore it.
     } else if (subscription != null) { // If someone has made a mistake and added this Subscriber multiple times, let's handle it gracefully
       try {
         s.cancel(); // Cancel the additional subscription to follow rule 2.5
       } catch(final Throwable t) {
         //Subscription.cancel is not allowed to throw an exception, according to rule 3.15
         (new IllegalStateException(s + " violated the Reactive Streams rule 3.15 by throwing an exception from cancel.", t)).printStackTrace(System.err);
       }
     } else {
       // We have to assign it locally before we use it, if we want to be a synchronous `Subscriber`
       // Because according to rule 3.10, the Subscription is allowed to call `onNext` synchronously from within `request`
       subscription = s;
       try {
         // If we want elements, according to rule 2.1 we need to call `request`
         // And, according to rule 3.2 we are allowed to call this synchronously from within the `onSubscribe` method
         s.request(1); // Our Subscriber is unbuffered and modest, it requests one element at a time
       } catch(final Throwable t) {
         // Subscription.request is not allowed to throw according to rule 3.16
         (new IllegalStateException(s + " violated the Reactive Streams rule 3.16 by throwing an exception from request.", t)).printStackTrace(System.err);
       }
     }
   }

   private final void handleOnNext(final T element) {
     if (!done) { // If we aren't already done
       if(subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
         // Check for spec violation of 2.1 and 1.09
         (new IllegalStateException("Someone violated the Reactive Streams rule 1.09 and 2.1 by signalling OnNext before `Subscription.request`. (no Subscription)")).printStackTrace(System.err);
       } else {
         try {
           if (whenNext(element)) {
             try {
               subscription.request(1); // Our Subscriber is unbuffered and modest, it requests one element at a time
             } catch(final Throwable t) {
               // Subscription.request is not allowed to throw according to rule 3.16
               (new IllegalStateException(subscription + " violated the Reactive Streams rule 3.16 by throwing an exception from request.", t)).printStackTrace(System.err);
             }
           } else {
             done(); // This is legal according to rule 2.6
           }
         } catch(final Throwable t) {
           done();
           try {
             onError(t);
           } catch(final Throwable t2) {
             //Subscriber.onError is not allowed to throw an exception, according to rule 2.13
             (new IllegalStateException(this + " violated the Reactive Streams rule 2.13 by throwing an exception from onError.", t2)).printStackTrace(System.err);
           }
         }
       }
     }
   }

   // Here it is important that we do not violate 2.2 and 2.3 by calling methods on the `Subscription` or `Publisher`
   private void handleOnComplete() {
     if (subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
       // Publisher is not allowed to signal onComplete before onSubscribe according to rule 1.09
       (new IllegalStateException("Publisher violated the Reactive Streams rule 1.09 signalling onComplete prior to onSubscribe.")).printStackTrace(System.err);
     } else {
       done = true; // Obey rule 2.4
       whenComplete();
     }
   }

   // Here it is important that we do not violate 2.2 and 2.3 by calling methods on the `Subscription` or `Publisher`
   private void handleOnError(final Throwable error) {
     if (subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
       // Publisher is not allowed to signal onError before onSubscribe according to rule 1.09
       (new IllegalStateException("Publisher violated the Reactive Streams rule 1.09 signalling onError prior to onSubscribe.")).printStackTrace(System.err);
     } else {
       done = true; // Obey rule 2.4
       whenError(error);
     }
   }

   // We implement the OnX methods on `Subscriber` to send Signals that we will process asycnhronously, but only one at a time

   @Override public final void onSubscribe(final Subscription s) {
     // As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `Subscription` is `null`
     if (s == null) throw null;

     signal(new OnSubscribe(s));
   }

   @Override public final void onNext(final T element) {
     // As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `element` is `null`
     if (element == null) throw null;

     signal(new OnNext<T>(element));
   }

   @Override public final void onError(final Throwable t) {
     // As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `Throwable` is `null`
     if (t == null) throw null;

     signal(new OnError(t));
   }

   @Override public final void onComplete() {
      signal(OnComplete.Instance);
   }

   // This `ConcurrentLinkedQueue` will track signals that are sent to this `Subscriber`, like `OnComplete` and `OnNext` ,
   // and obeying rule 2.11
   private final ConcurrentLinkedQueue<Signal> inboundSignals = new ConcurrentLinkedQueue<Signal>();

   // We are using this `AtomicBoolean` to make sure that this `Subscriber` doesn't run concurrently with itself,
   // obeying rule 2.7 and 2.11
   private final AtomicBoolean on = new AtomicBoolean(false);

    @SuppressWarnings("unchecked")
    @Override public final void run() {
     if(on.get()) { // establishes a happens-before relationship with the end of the previous run
       try {
         final Signal s = inboundSignals.poll(); // We take a signal off the queue
         if (!done) { // If we're done, we shouldn't process any more signals, obeying rule 2.8
           // Below we simply unpack the `Signal`s and invoke the corresponding methods
           if (s instanceof OnNext<?>)
             handleOnNext(((OnNext<T>)s).next);
           else if (s instanceof OnSubscribe)
             handleOnSubscribe(((OnSubscribe)s).subscription);
           else if (s instanceof OnError) // We are always able to handle OnError, obeying rule 2.10
             handleOnError(((OnError)s).error);
           else if (s == OnComplete.Instance) // We are always able to handle OnComplete, obeying rule 2.9
             handleOnComplete();
         }
       } finally {
         on.set(false); // establishes a happens-before relationship with the beginning of the next run
         if(!inboundSignals.isEmpty()) // If we still have signals to process
           tryScheduleToExecute(); // Then we try to schedule ourselves to execute again
       }
     }
   }

   // What `signal` does is that it sends signals to the `Subscription` asynchronously
   private void signal(final Signal signal) {
     if (inboundSignals.offer(signal)) // No need to null-check here as ConcurrentLinkedQueue does this for us
       tryScheduleToExecute(); // Then we try to schedule it for execution, if it isn't already
   }

   // This method makes sure that this `Subscriber` is only executing on one Thread at a time
   private final void tryScheduleToExecute() {
     if(on.compareAndSet(false, true)) {
       try {
         executor.execute(this);
       } catch(Throwable t) { // If we can't run on the `Executor`, we need to fail gracefully and not violate rule 2.13
         if (!done) {
           try {
             done(); // First of all, this failure is not recoverable, so we need to cancel our subscription
           } finally {
             inboundSignals.clear(); // We're not going to need these anymore
             // This subscription is cancelled by now, but letting the Subscriber become schedulable again means
             // that we can drain the inboundSignals queue if anything arrives after clearing
             on.set(false);
           }
         }
       }
     }
   }
 }
	/*
	* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
	* 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.
	*
	* 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.
	*/

	package org.reactivestreams.example.unicast;

	import org.reactivestreams.Subscriber;
	import org.reactivestreams.Subscription;

	import java.util.concurrent.Executor;
	import java.util.concurrent.atomic.AtomicBoolean;
	import java.util.concurrent.ConcurrentLinkedQueue;

	/**
	* AsyncSubscriber is an implementation of Reactive Streams `Subscriber`,
	* it runs asynchronously (on an Executor), requests one element
	* at a time, and invokes a user-defined method to process each element.
	*
	* NOTE: The code below uses a lot of try-catches to show the reader where exceptions can be expected, and where they are forbidden.
	*/
	public abstract class AsyncSubscriber<T> implements Subscriber<T>, Runnable {

	// Signal represents the asynchronous protocol between the Publisher and Subscriber
	private static interface Signal {}

	private enum OnComplete implements Signal { Instance; }

	private static class OnError implements Signal {
	public final Throwable error;
	public OnError(final Throwable error) { this.error = error; }
	}

	private static class OnNext<T> implements Signal {
	public final T next;
	public OnNext(final T next) { this.next = next; }
	}

	private static class OnSubscribe implements Signal {
	public final Subscription subscription;
	public OnSubscribe(final Subscription subscription) { this.subscription = subscription; }
	}

	private Subscription subscription; // Obeying rule 3.1, we make this private!
	private boolean done; // It's useful to keep track of whether this Subscriber is done or not
	private final Executor executor; // This is the Executor we'll use to be asynchronous, obeying rule 2.2

	// Only one constructor, and it's only accessible for the subclasses
	protected AsyncSubscriber(Executor executor) {
	if (executor == null) throw null;
	this.executor = executor;
	}

	// Showcases a convenience method to idempotently marking the Subscriber as "done", so we don't want to process more elements
	// herefor we also need to cancel our `Subscription`.
	private final void done() {
	//On this line we could add a guard against `!done`, but since rule 3.7 says that `Subscription.cancel()` is idempotent, we don't need to.
	done = true; // If `whenNext` throws an exception, let's consider ourselves done (not accepting more elements)
	if (subscription != null) { // If we are bailing out before we got a `Subscription` there's little need for cancelling it.
	try {
	subscription.cancel(); // Cancel the subscription
	} catch(final Throwable t) {
	//Subscription.cancel is not allowed to throw an exception, according to rule 3.15
	(new IllegalStateException(subscription + " violated the Reactive Streams rule 3.15 by throwing an exception from cancel.", t)).printStackTrace(System.err);
	}
	}
	}

	// This method is invoked when the OnNext signals arrive
	// Returns whether more elements are desired or not, and if no more elements are desired,
	// for convenience.
	protected abstract boolean whenNext(final T element);

	// This method is invoked when the OnComplete signal arrives
	// override this method to implement your own custom onComplete logic.
	protected void whenComplete() { }

	// This method is invoked if the OnError signal arrives
	// override this method to implement your own custom onError logic.
	protected void whenError(Throwable error) { }

	private final void handleOnSubscribe(final Subscription s) {
	if (s == null) {
	// Getting a null `Subscription` here is not valid so lets just ignore it.
	} else if (subscription != null) { // If someone has made a mistake and added this Subscriber multiple times, let's handle it gracefully
	try {
	s.cancel(); // Cancel the additional subscription to follow rule 2.5
	} catch(final Throwable t) {
	//Subscription.cancel is not allowed to throw an exception, according to rule 3.15
	(new IllegalStateException(s + " violated the Reactive Streams rule 3.15 by throwing an exception from cancel.", t)).printStackTrace(System.err);
	}
	} else {
	// We have to assign it locally before we use it, if we want to be a synchronous `Subscriber`
	// Because according to rule 3.10, the Subscription is allowed to call `onNext` synchronously from within `request`
	subscription = s;
	try {
	// If we want elements, according to rule 2.1 we need to call `request`
	// And, according to rule 3.2 we are allowed to call this synchronously from within the `onSubscribe` method
	s.request(1); // Our Subscriber is unbuffered and modest, it requests one element at a time
	} catch(final Throwable t) {
	// Subscription.request is not allowed to throw according to rule 3.16
	(new IllegalStateException(s + " violated the Reactive Streams rule 3.16 by throwing an exception from request.", t)).printStackTrace(System.err);
	}
	}
	}

	private final void handleOnNext(final T element) {
	if (!done) { // If we aren't already done
	if(subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
	// Check for spec violation of 2.1 and 1.09
	(new IllegalStateException("Someone violated the Reactive Streams rule 1.09 and 2.1 by signalling OnNext before `Subscription.request`. (no Subscription)")).printStackTrace(System.err);
	} else {
	try {
	if (whenNext(element)) {
	try {
	subscription.request(1); // Our Subscriber is unbuffered and modest, it requests one element at a time
	} catch(final Throwable t) {
	// Subscription.request is not allowed to throw according to rule 3.16
	(new IllegalStateException(subscription + " violated the Reactive Streams rule 3.16 by throwing an exception from request.", t)).printStackTrace(System.err);
	}
	} else {
	done(); // This is legal according to rule 2.6
	}
	} catch(final Throwable t) {
	done();
	try {
	onError(t);
	} catch(final Throwable t2) {
	//Subscriber.onError is not allowed to throw an exception, according to rule 2.13
	(new IllegalStateException(this + " violated the Reactive Streams rule 2.13 by throwing an exception from onError.", t2)).printStackTrace(System.err);
	}
	}
	}
	}
	}

	// Here it is important that we do not violate 2.2 and 2.3 by calling methods on the `Subscription` or `Publisher`
	private void handleOnComplete() {
	if (subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
	// Publisher is not allowed to signal onComplete before onSubscribe according to rule 1.09
	(new IllegalStateException("Publisher violated the Reactive Streams rule 1.09 signalling onComplete prior to onSubscribe.")).printStackTrace(System.err);
	} else {
	done = true; // Obey rule 2.4
	whenComplete();
	}
	}

	// Here it is important that we do not violate 2.2 and 2.3 by calling methods on the `Subscription` or `Publisher`
	private void handleOnError(final Throwable error) {
	if (subscription == null) { // Technically this check is not needed, since we are expecting Publishers to conform to the spec
	// Publisher is not allowed to signal onError before onSubscribe according to rule 1.09
	(new IllegalStateException("Publisher violated the Reactive Streams rule 1.09 signalling onError prior to onSubscribe.")).printStackTrace(System.err);
	} else {
	done = true; // Obey rule 2.4
	whenError(error);
	}
	}

	// We implement the OnX methods on `Subscriber` to send Signals that we will process asycnhronously, but only one at a time

	@Override public final void onSubscribe(final Subscription s) {
	// As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `Subscription` is `null`
	if (s == null) throw null;

	signal(new OnSubscribe(s));
	}

	@Override public final void onNext(final T element) {
	// As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `element` is `null`
	if (element == null) throw null;

	signal(new OnNext<T>(element));
	}

	@Override public final void onError(final Throwable t) {
	// As per rule 2.13, we need to throw a `java.lang.NullPointerException` if the `Throwable` is `null`
	if (t == null) throw null;

	signal(new OnError(t));
	}

	@Override public final void onComplete() {
	signal(OnComplete.Instance);
	}

	// This `ConcurrentLinkedQueue` will track signals that are sent to this `Subscriber`, like `OnComplete` and `OnNext` ,
	// and obeying rule 2.11
	private final ConcurrentLinkedQueue<Signal> inboundSignals = new ConcurrentLinkedQueue<Signal>();

	// We are using this `AtomicBoolean` to make sure that this `Subscriber` doesn't run concurrently with itself,
	// obeying rule 2.7 and 2.11
	private final AtomicBoolean on = new AtomicBoolean(false);

	@SuppressWarnings("unchecked")
	@Override public final void run() {
	if(on.get()) { // establishes a happens-before relationship with the end of the previous run
	try {
	final Signal s = inboundSignals.poll(); // We take a signal off the queue
	if (!done) { // If we're done, we shouldn't process any more signals, obeying rule 2.8
	// Below we simply unpack the `Signal`s and invoke the corresponding methods
	if (s instanceof OnNext<?>)
	handleOnNext(((OnNext<T>)s).next);
	else if (s instanceof OnSubscribe)
	handleOnSubscribe(((OnSubscribe)s).subscription);
	else if (s instanceof OnError) // We are always able to handle OnError, obeying rule 2.10
	handleOnError(((OnError)s).error);
	else if (s == OnComplete.Instance) // We are always able to handle OnComplete, obeying rule 2.9
	handleOnComplete();
	}
	} finally {
	on.set(false); // establishes a happens-before relationship with the beginning of the next run
	if(!inboundSignals.isEmpty()) // If we still have signals to process
	tryScheduleToExecute(); // Then we try to schedule ourselves to execute again
	}
	}
	}

	// What `signal` does is that it sends signals to the `Subscription` asynchronously
	private void signal(final Signal signal) {
	if (inboundSignals.offer(signal)) // No need to null-check here as ConcurrentLinkedQueue does this for us
	tryScheduleToExecute(); // Then we try to schedule it for execution, if it isn't already
	}

	// This method makes sure that this `Subscriber` is only executing on one Thread at a time
	private final void tryScheduleToExecute() {
	if(on.compareAndSet(false, true)) {
	try {
	executor.execute(this);
	} catch(Throwable t) { // If we can't run on the `Executor`, we need to fail gracefully and not violate rule 2.13
	if (!done) {
	try {
	done(); // First of all, this failure is not recoverable, so we need to cancel our subscription
	} finally {
	inboundSignals.clear(); // We're not going to need these anymore
	// This subscription is cancelled by now, but letting the Subscriber become schedulable again means
	// that we can drain the inboundSignals queue if anything arrives after clearing
	on.set(false);
	}
	}
	}
	}
	}
	}