https://github.com/ReactiveX/RxJava: Reactive Extensions for Java
  • David Karnok 
Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.

/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.processors;

import java.lang.reflect.Array;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;

import org.reactivestreams.*;

import io.reactivex.annotations.*;
import io.reactivex.exceptions.MissingBackpressureException;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.*;
import io.reactivex.internal.util.AppendOnlyLinkedArrayList.NonThrowingPredicate;
import io.reactivex.plugins.RxJavaPlugins;


Processor that emits the most recent item it has observed and all subsequent observed items to each subscribed Subscriber. 



 This processor does not have a public constructor by design; a new empty instance of this BehaviorProcessor can be created via the create() method and a new non-empty instance can be created via createDefault(Object) (named as such to avoid overload resolution conflict with Flowable.create that creates a Flowable, not a BehaviorProcessor). 

In accordance with the Reactive Streams specification (Rule 2.13) nulls are not allowed as default initial values in createDefault(Object) or as parameters to onNext(Object) and onError(Throwable). 
 When this BehaviorProcessor is terminated via onError(Throwable) or onComplete(), the last observed item (if any) is cleared and late Subscribers only receive the respective terminal event. 
 The BehaviorProcessor does not support clearing its cached value (to appear empty again), however, the effect can be achieved by using a special item and making sure Subscribers subscribe through a filter whose predicate filters out this special item: 

BehaviorProcessor<Integer> processor = BehaviorProcessor.create();
final Integer EMPTY = Integer.MIN_VALUE;
Flowable<Integer> flowable = processor.filter(v -> v != EMPTY);
TestSubscriber<Integer> ts1 = flowable.test();
processor.onNext(1);
// this will "clear" the cache
processor.onNext(EMPTY);
TestSubscriber<Integer> ts2 = flowable.test();
processor.onNext(2);
processor.onComplete();
// ts1 received both non-empty items
ts1.assertResult(1, 2);
// ts2 received only 2 even though the current item was EMPTY
// when it got subscribed
ts2.assertResult(2);
// Subscribers coming after the processor was terminated receive
// no items and only the onComplete event in this case.
flowable.test().assertResult();



 Even though BehaviorProcessor implements the Subscriber interface, calling onSubscribe is not required (Rule 2.12) if the processor is used as a standalone source. However, calling onSubscribe after the BehaviorProcessor reached its terminal state will result in the given Subscription being cancelled immediately. 
 Calling onNext(Object), offer(Object), onError(Throwable) and onComplete() is required to be serialized (called from the same thread or called non-overlappingly from different threads through external means of serialization). The FlowableProcessor.toSerialized() method available to all FlowableProcessors provides such serialization and also protects against reentrance (i.e., when a downstream Subscriber consuming this processor also wants to call onNext(Object) on this processor recursively). Note that serializing over offer(Object) is not supported through toSerialized() because it is a method available on the PublishProcessor and BehaviorProcessor classes only. 
 This BehaviorProcessor supports the standard state-peeking methods hasComplete(), hasThrowable(), getThrowable() and hasSubscribers() as well as means to read the latest observed value in a non-blocking and thread-safe manner via hasValue(), getValue(), getValues() or getValues(Object[]). 
 Note that this processor signals MissingBackpressureException if a particular Subscriber is not ready to receive onNext events. To avoid this exception being signaled, use offer(Object) to only try to emit an item when all Subscribers have requested item(s). 

 
Backpressure:

 
The BehaviorProcessor does not coordinate requests of its downstream Subscribers and expects each individual Subscriber is ready to receive onNext items when onNext(Object) is called. If a Subscriber is not ready, a MissingBackpressureException is signalled to it. To avoid overflowing the current Subscribers, the conditional offer(Object) method is available that returns true if any of the Subscribers is not ready to receive onNext events. If there are no Subscribers to the processor, offer() always succeeds. If the BehaviorProcessor is (optionally) subscribed to another Publisher, this upstream Publisher is consumed in an unbounded fashion (requesting Long.MAX_VALUE).

 
Scheduler:

 
BehaviorProcessor does not operate by default on a particular Scheduler and the Subscribers get notified on the thread the respective onXXX methods were invoked.

 
Error handling:

 
When the onError(Throwable) is called, the BehaviorProcessor enters into a terminal state and emits the same Throwable instance to the last set of Subscribers. During this emission, if one or more Subscribers cancel their respective Subscriptions, the Throwable is delivered to the global error handler via RxJavaPlugins.onError(Throwable) (multiple times if multiple Subscribers cancel at once). If there were no Subscribers subscribed to this BehaviorProcessor when the onError() was called, the global error handler is not invoked. 





Example usage:

 
// subscriber will receive all events.
BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
processor.subscribe(subscriber);
processor.onNext("one");
processor.onNext("two");
processor.onNext("three");
// subscriber will receive the "one", "two" and "three" events, but not "zero"
BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
processor.onNext("zero");
processor.onNext("one");
processor.subscribe(subscriber);
processor.onNext("two");
processor.onNext("three");
// subscriber will receive only onComplete
BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
processor.onNext("zero");
processor.onNext("one");
processor.onComplete();
processor.subscribe(subscriber);
// subscriber will receive only onError
BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
processor.onNext("zero");
processor.onNext("one");
processor.onError(new RuntimeException("error"));
processor.subscribe(subscriber);
 


Type parameters:
  • <T> – 
         the type of item expected to be observed and emitted by the Processor
/**
 * Processor that emits the most recent item it has observed and all subsequent observed items to each subscribed
 * {@link Subscriber}.
 * <p>
 * <img width="640" height="460" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/S.BehaviorProcessor.png" alt="">
 * <p>
 * This processor does not have a public constructor by design; a new empty instance of this
 * {@code BehaviorProcessor} can be created via the {@link #create()} method and
 * a new non-empty instance can be created via {@link #createDefault(Object)} (named as such to avoid
 * overload resolution conflict with {@code Flowable.create} that creates a Flowable, not a {@code BehaviorProcessor}).
 * <p>
 * In accordance with the Reactive Streams specification (<a href="https://github.com/reactive-streams/reactive-streams-jvm#2.13">Rule 2.13</a>)
 * {@code null}s are not allowed as default initial values in {@link #createDefault(Object)} or as parameters to {@link #onNext(Object)} and
 * {@link #onError(Throwable)}.
 * <p>
 * When this {@code BehaviorProcessor} is terminated via {@link #onError(Throwable)} or {@link #onComplete()}, the
 * last observed item (if any) is cleared and late {@link org.reactivestreams.Subscriber}s only receive
 * the respective terminal event.
 * <p>
 * The {@code BehaviorProcessor} does not support clearing its cached value (to appear empty again), however, the
 * effect can be achieved by using a special item and making sure {@code Subscriber}s subscribe through a
 * filter whose predicate filters out this special item:
 * <pre><code>
 * BehaviorProcessor&lt;Integer&gt; processor = BehaviorProcessor.create();
 *
 * final Integer EMPTY = Integer.MIN_VALUE;
 *
 * Flowable&lt;Integer&gt; flowable = processor.filter(v -&gt; v != EMPTY);
 *
 * TestSubscriber&lt;Integer&gt; ts1 = flowable.test();
 *
 * processor.onNext(1);
 * // this will "clear" the cache
 * processor.onNext(EMPTY);
 * 
 * TestSubscriber&lt;Integer&gt; ts2 = flowable.test();
 * 
 * processor.onNext(2);
 * processor.onComplete();
 * 
 * // ts1 received both non-empty items
 * ts1.assertResult(1, 2);
 * 
 * // ts2 received only 2 even though the current item was EMPTY
 * // when it got subscribed
 * ts2.assertResult(2);
 * 
 * // Subscribers coming after the processor was terminated receive
 * // no items and only the onComplete event in this case.
 * flowable.test().assertResult();
 * </code></pre>
 * <p>
 * Even though {@code BehaviorProcessor} implements the {@code Subscriber} interface, calling
 * {@code onSubscribe} is not required (<a href="https://github.com/reactive-streams/reactive-streams-jvm#2.12">Rule 2.12</a>)
 * if the processor is used as a standalone source. However, calling {@code onSubscribe}
 * after the {@code BehaviorProcessor} reached its terminal state will result in the
 * given {@code Subscription} being cancelled immediately.
 * <p>
 * Calling {@link #onNext(Object)}, {@link #offer(Object)}, {@link #onError(Throwable)} and {@link #onComplete()}
 * is required to be serialized (called from the same thread or called non-overlappingly from different threads
 * through external means of serialization). The {@link #toSerialized()} method available to all {@code FlowableProcessor}s
 * provides such serialization and also protects against reentrance (i.e., when a downstream {@code Subscriber}
 * consuming this processor also wants to call {@link #onNext(Object)} on this processor recursively).
 * Note that serializing over {@link #offer(Object)} is not supported through {@code toSerialized()} because it is a method
 * available on the {@code PublishProcessor} and {@code BehaviorProcessor} classes only.
 * <p>
 * This {@code BehaviorProcessor} supports the standard state-peeking methods {@link #hasComplete()}, {@link #hasThrowable()},
 * {@link #getThrowable()} and {@link #hasSubscribers()} as well as means to read the latest observed value
 * in a non-blocking and thread-safe manner via {@link #hasValue()}, {@link #getValue()},
 * {@link #getValues()} or {@link #getValues(Object[])}.
 * <p>
 * Note that this processor signals {@code MissingBackpressureException} if a particular {@code Subscriber} is not
 * ready to receive {@code onNext} events. To avoid this exception being signaled, use {@link #offer(Object)} to only
 * try to emit an item when all {@code Subscriber}s have requested item(s).
 * <dl>
 *  <dt><b>Backpressure:</b></dt>
 *  <dd>The {@code BehaviorProcessor} does not coordinate requests of its downstream {@code Subscriber}s and
 *  expects each individual {@code Subscriber} is ready to receive {@code onNext} items when {@link #onNext(Object)}
 *  is called. If a {@code Subscriber} is not ready, a {@code MissingBackpressureException} is signalled to it.
 *  To avoid overflowing the current {@code Subscriber}s, the conditional {@link #offer(Object)} method is available
 *  that returns true if any of the {@code Subscriber}s is not ready to receive {@code onNext} events. If
 *  there are no {@code Subscriber}s to the processor, {@code offer()} always succeeds.
 *  If the {@code BehaviorProcessor} is (optionally) subscribed to another {@code Publisher}, this upstream
 *  {@code Publisher} is consumed in an unbounded fashion (requesting {@code Long.MAX_VALUE}).</dd>
 *  <dt><b>Scheduler:</b></dt>
 *  <dd>{@code BehaviorProcessor} does not operate by default on a particular {@link io.reactivex.Scheduler} and
 *  the {@code Subscriber}s get notified on the thread the respective {@code onXXX} methods were invoked.</dd>
 *  <dt><b>Error handling:</b></dt>
 *  <dd>When the {@link #onError(Throwable)} is called, the {@code BehaviorProcessor} enters into a terminal state
 *  and emits the same {@code Throwable} instance to the last set of {@code Subscriber}s. During this emission,
 *  if one or more {@code Subscriber}s cancel their respective {@code Subscription}s, the
 *  {@code Throwable} is delivered to the global error handler via
 *  {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} (multiple times if multiple {@code Subscriber}s
 *  cancel at once).
 *  If there were no {@code Subscriber}s subscribed to this {@code BehaviorProcessor} when the {@code onError()}
 *  was called, the global error handler is not invoked.
 *  </dd>
 * </dl>
 * <p>
 * Example usage:
 * <pre> {@code

  // subscriber will receive all events.
  BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
  processor.subscribe(subscriber);
  processor.onNext("one");
  processor.onNext("two");
  processor.onNext("three");

  // subscriber will receive the "one", "two" and "three" events, but not "zero"
  BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
  processor.onNext("zero");
  processor.onNext("one");
  processor.subscribe(subscriber);
  processor.onNext("two");
  processor.onNext("three");

  // subscriber will receive only onComplete
  BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
  processor.onNext("zero");
  processor.onNext("one");
  processor.onComplete();
  processor.subscribe(subscriber);

  // subscriber will receive only onError
  BehaviorProcessor<Object> processor = BehaviorProcessor.create("default");
  processor.onNext("zero");
  processor.onNext("one");
  processor.onError(new RuntimeException("error"));
  processor.subscribe(subscriber);
  } </pre>
 *
 * @param <T>
 *          the type of item expected to be observed and emitted by the Processor
 */
public final class BehaviorProcessor<T> extends FlowableProcessor<T> {
    final AtomicReference<BehaviorSubscription<T>[]> subscribers;

    static final Object[] EMPTY_ARRAY = new Object[0];

    @SuppressWarnings("rawtypes")
    static final BehaviorSubscription[] EMPTY = new BehaviorSubscription[0];

    @SuppressWarnings("rawtypes")
    static final BehaviorSubscription[] TERMINATED = new BehaviorSubscription[0];

    final ReadWriteLock lock;
    final Lock readLock;
    final Lock writeLock;

    final AtomicReference<Object> value;

    final AtomicReference<Throwable> terminalEvent;

    long index;

    
Creates a BehaviorProcessor without a default item. 
Type parameters:
  • <T> – 
           the type of item the BehaviorProcessor will emit
Returns:the constructed BehaviorProcessor
/**
     * Creates a {@link BehaviorProcessor} without a default item.
     *
     * @param <T>
     *            the type of item the BehaviorProcessor will emit
     * @return the constructed {@link BehaviorProcessor}
     */
    @CheckReturnValue
    @NonNull
    public static <T> BehaviorProcessor<T> create() {
        return new BehaviorProcessor<T>();
    }

    
Creates a BehaviorProcessor that emits the last item it observed and all subsequent items to each Subscriber that subscribes to it. 
Params:
  • defaultValue –  the item that will be emitted first to any Subscriber as long as the BehaviorProcessor has not yet observed any items from its source Observable
Type parameters:
  • <T> – 
           the type of item the BehaviorProcessor will emit
Returns:the constructed BehaviorProcessor
/**
     * Creates a {@link BehaviorProcessor} that emits the last item it observed and all subsequent items to each
     * {@link Subscriber} that subscribes to it.
     *
     * @param <T>
     *            the type of item the BehaviorProcessor will emit
     * @param defaultValue
     *            the item that will be emitted first to any {@link Subscriber} as long as the
     *            {@link BehaviorProcessor} has not yet observed any items from its source {@code Observable}
     * @return the constructed {@link BehaviorProcessor}
     */
    @CheckReturnValue
    @NonNull
    public static <T> BehaviorProcessor<T> createDefault(T defaultValue) {
        ObjectHelper.requireNonNull(defaultValue, "defaultValue is null");
        return new BehaviorProcessor<T>(defaultValue);
    }

    
Constructs an empty BehaviorProcessor.

Since:2.0
/**
     * Constructs an empty BehaviorProcessor.
     * @since 2.0
     */
    @SuppressWarnings("unchecked")
    BehaviorProcessor() {
        this.value = new AtomicReference<Object>();
        this.lock = new ReentrantReadWriteLock();
        this.readLock = lock.readLock();
        this.writeLock = lock.writeLock();
        this.subscribers = new AtomicReference<BehaviorSubscription<T>[]>(EMPTY);
        this.terminalEvent = new AtomicReference<Throwable>();
    }

    
Constructs a BehaviorProcessor with the given initial value.

Params:
  • defaultValue – the initial value, not null (verified)
Throws:
Since:2.0
/**
     * Constructs a BehaviorProcessor with the given initial value.
     * @param defaultValue the initial value, not null (verified)
     * @throws NullPointerException if {@code defaultValue} is null
     * @since 2.0
     */
    BehaviorProcessor(T defaultValue) {
        this();
        this.value.lazySet(ObjectHelper.requireNonNull(defaultValue, "defaultValue is null"));
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        BehaviorSubscription<T> bs = new BehaviorSubscription<T>(s, this);
        s.onSubscribe(bs);
        if (add(bs)) {
            if (bs.cancelled) {
                remove(bs);
            } else {
                bs.emitFirst();
            }
        } else {
            Throwable ex = terminalEvent.get();
            if (ex == ExceptionHelper.TERMINATED) {
                s.onComplete();
            } else {
                s.onError(ex);
            }
        }
    }

    @Override
    public void onSubscribe(Subscription s) {
        if (terminalEvent.get() != null) {
            s.cancel();
            return;
        }
        s.request(Long.MAX_VALUE);
    }

    @Override
    public void onNext(T t) {
        ObjectHelper.requireNonNull(t, "onNext called with null. Null values are generally not allowed in 2.x operators and sources.");

        if (terminalEvent.get() != null) {
            return;
        }
        Object o = NotificationLite.next(t);
        setCurrent(o);
        for (BehaviorSubscription<T> bs : subscribers.get()) {
            bs.emitNext(o, index);
        }
    }

    @Override
    public void onError(Throwable t) {
        ObjectHelper.requireNonNull(t, "onError called with null. Null values are generally not allowed in 2.x operators and sources.");
        if (!terminalEvent.compareAndSet(null, t)) {
            RxJavaPlugins.onError(t);
            return;
        }
        Object o = NotificationLite.error(t);
        for (BehaviorSubscription<T> bs : terminate(o)) {
            bs.emitNext(o, index);
        }
    }

    @Override
    public void onComplete() {
        if (!terminalEvent.compareAndSet(null, ExceptionHelper.TERMINATED)) {
            return;
        }
        Object o = NotificationLite.complete();
        for (BehaviorSubscription<T> bs : terminate(o)) {
            bs.emitNext(o, index);  // relaxed read okay since this is the only mutator thread
        }
    }

    
Tries to emit the item to all currently subscribed Subscribers if all of them
has requested some value, returns false otherwise.


This method should be called in a sequential manner just like the onXXX methods
of the PublishProcessor.


Calling with null will terminate the PublishProcessor and a NullPointerException
is signalled to the Subscribers.

History: 2.0.8 - experimental

Params:
  • t – the item to emit, not null
Returns:true if the item was emitted to all Subscribers
Since:2.2
/**
     * Tries to emit the item to all currently subscribed Subscribers if all of them
     * has requested some value, returns false otherwise.
     * <p>
     * This method should be called in a sequential manner just like the onXXX methods
     * of the PublishProcessor.
     * <p>
     * Calling with null will terminate the PublishProcessor and a NullPointerException
     * is signalled to the Subscribers.
     * <p>History: 2.0.8 - experimental
     * @param t the item to emit, not null
     * @return true if the item was emitted to all Subscribers
     * @since 2.2
     */
    public boolean offer(T t) {
        if (t == null) {
            onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
            return true;
        }
        BehaviorSubscription<T>[] array = subscribers.get();

        for (BehaviorSubscription<T> s : array) {
            if (s.isFull()) {
                return false;
            }
        }

        Object o = NotificationLite.next(t);
        setCurrent(o);
        for (BehaviorSubscription<T> bs : array) {
            bs.emitNext(o, index);
        }
        return true;
    }

    @Override
    public boolean hasSubscribers() {
        return subscribers.get().length != 0;
    }

    /* test support*/ int subscriberCount() {
        return subscribers.get().length;
    }

    @Override
    @Nullable
    public Throwable getThrowable() {
        Object o = value.get();
        if (NotificationLite.isError(o)) {
            return NotificationLite.getError(o);
        }
        return null;
    }

    
Returns a single value the BehaviorProcessor currently has or null if no such value exists.

The method is thread-safe.

Returns:a single value the BehaviorProcessor currently has or null if no such value exists
/**
     * Returns a single value the BehaviorProcessor currently has or null if no such value exists.
     * <p>The method is thread-safe.
     * @return a single value the BehaviorProcessor currently has or null if no such value exists
     */
    @Nullable
    public T getValue() {
        Object o = value.get();
        if (NotificationLite.isComplete(o) || NotificationLite.isError(o)) {
            return null;
        }
        return NotificationLite.getValue(o);
    }

    
Returns an Object array containing snapshot all values of the BehaviorProcessor.

The method is thread-safe.

Returns:the array containing the snapshot of all values of the BehaviorProcessor
Deprecated:in 2.1.14; put the result of getValue() into an array manually, will be removed in 3.x
/**
     * Returns an Object array containing snapshot all values of the BehaviorProcessor.
     * <p>The method is thread-safe.
     * @return the array containing the snapshot of all values of the BehaviorProcessor
     * @deprecated in 2.1.14; put the result of {@link #getValue()} into an array manually, will be removed in 3.x
     */
    @Deprecated
    public Object[] getValues() {
        @SuppressWarnings("unchecked")
        T[] a = (T[])EMPTY_ARRAY;
        T[] b = getValues(a);
        if (b == EMPTY_ARRAY) {
            return new Object[0];
        }
        return b;

    }

    
Returns a typed array containing a snapshot of all values of the BehaviorProcessor.

The method follows the conventions of Collection.toArray by setting the array element
after the last value to null (if the capacity permits).

The method is thread-safe.

Params:
  • array – the target array to copy values into if it fits
Returns:the given array if the values fit into it or a new array containing all values
Deprecated:in 2.1.14; put the result of getValue() into an array manually, will be removed in 3.x
/**
     * Returns a typed array containing a snapshot of all values of the BehaviorProcessor.
     * <p>The method follows the conventions of Collection.toArray by setting the array element
     * after the last value to null (if the capacity permits).
     * <p>The method is thread-safe.
     * @param array the target array to copy values into if it fits
     * @return the given array if the values fit into it or a new array containing all values
     * @deprecated in 2.1.14; put the result of {@link #getValue()} into an array manually, will be removed in 3.x
     */
    @Deprecated
    @SuppressWarnings("unchecked")
    public T[] getValues(T[] array) {
        Object o = value.get();
        if (o == null || NotificationLite.isComplete(o) || NotificationLite.isError(o)) {
            if (array.length != 0) {
                array[0] = null;
            }
            return array;
        }
        T v = NotificationLite.getValue(o);
        if (array.length != 0) {
            array[0] = v;
            if (array.length != 1) {
                array[1] = null;
            }
        } else {
            array = (T[])Array.newInstance(array.getClass().getComponentType(), 1);
            array[0] = v;
        }
        return array;
    }

    @Override
    public boolean hasComplete() {
        Object o = value.get();
        return NotificationLite.isComplete(o);
    }

    @Override
    public boolean hasThrowable() {
        Object o = value.get();
        return NotificationLite.isError(o);
    }

    
Returns true if the BehaviorProcessor has any value.

The method is thread-safe.

Returns:true if the BehaviorProcessor has any value
/**
     * Returns true if the BehaviorProcessor has any value.
     * <p>The method is thread-safe.
     * @return true if the BehaviorProcessor has any value
     */
    public boolean hasValue() {
        Object o = value.get();
        return o != null && !NotificationLite.isComplete(o) && !NotificationLite.isError(o);
    }

    boolean add(BehaviorSubscription<T> rs) {
        for (;;) {
            BehaviorSubscription<T>[] a = subscribers.get();
            if (a == TERMINATED) {
                return false;
            }
            int len = a.length;
            @SuppressWarnings("unchecked")
            BehaviorSubscription<T>[] b = new BehaviorSubscription[len + 1];
            System.arraycopy(a, 0, b, 0, len);
            b[len] = rs;
            if (subscribers.compareAndSet(a, b)) {
                return true;
            }
        }
    }

    @SuppressWarnings("unchecked")
    void remove(BehaviorSubscription<T> rs) {
        for (;;) {
            BehaviorSubscription<T>[] a = subscribers.get();
            int len = a.length;
            if (len == 0) {
                return;
            }
            int j = -1;
            for (int i = 0; i < len; i++) {
                if (a[i] == rs) {
                    j = i;
                    break;
                }
            }

            if (j < 0) {
                return;
            }
            BehaviorSubscription<T>[] b;
            if (len == 1) {
                b = EMPTY;
            } else {
                b = new BehaviorSubscription[len - 1];
                System.arraycopy(a, 0, b, 0, j);
                System.arraycopy(a, j + 1, b, j, len - j - 1);
            }
            if (subscribers.compareAndSet(a, b)) {
                return;
            }
        }
    }

    @SuppressWarnings("unchecked")
    BehaviorSubscription<T>[] terminate(Object terminalValue) {

        BehaviorSubscription<T>[] a = subscribers.get();
        if (a != TERMINATED) {
            a = subscribers.getAndSet(TERMINATED);
            if (a != TERMINATED) {
                // either this or atomics with lots of allocation
                setCurrent(terminalValue);
            }
        }

        return a;
    }

    void setCurrent(Object o) {
        Lock wl = writeLock;
        wl.lock();
        index++;
        value.lazySet(o);
        wl.unlock();
    }

    static final class BehaviorSubscription<T> extends AtomicLong implements Subscription, NonThrowingPredicate<Object> {

        private static final long serialVersionUID = 3293175281126227086L;

        final Subscriber<? super T> downstream;
        final BehaviorProcessor<T> state;

        boolean next;
        boolean emitting;
        AppendOnlyLinkedArrayList<Object> queue;

        boolean fastPath;

        volatile boolean cancelled;

        long index;

        BehaviorSubscription(Subscriber<? super T> actual, BehaviorProcessor<T> state) {
            this.downstream = actual;
            this.state = state;
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(this, n);
            }
        }

        @Override
        public void cancel() {
            if (!cancelled) {
                cancelled = true;

                state.remove(this);
            }
        }

        void emitFirst() {
            if (cancelled) {
                return;
            }
            Object o;
            synchronized (this) {
                if (cancelled) {
                    return;
                }
                if (next) {
                    return;
                }

                BehaviorProcessor<T> s = state;

                Lock readLock = s.readLock;
                readLock.lock();
                index = s.index;
                o = s.value.get();
                readLock.unlock();

                emitting = o != null;
                next = true;
            }

            if (o != null) {
                if (test(o)) {
                    return;
                }

                emitLoop();
            }
        }

        void emitNext(Object value, long stateIndex) {
            if (cancelled) {
                return;
            }
            if (!fastPath) {
                synchronized (this) {
                    if (cancelled) {
                        return;
                    }
                    if (index == stateIndex) {
                        return;
                    }
                    if (emitting) {
                        AppendOnlyLinkedArrayList<Object> q = queue;
                        if (q == null) {
                            q = new AppendOnlyLinkedArrayList<Object>(4);
                            queue = q;
                        }
                        q.add(value);
                        return;
                    }
                    next = true;
                }
                fastPath = true;
            }

            test(value);
        }

        @Override
        public boolean test(Object o) {
            if (cancelled) {
                return true;
            }

            if (NotificationLite.isComplete(o)) {
                downstream.onComplete();
                return true;
            } else
            if (NotificationLite.isError(o)) {
                downstream.onError(NotificationLite.getError(o));
                return true;
            }

            long r = get();
            if (r != 0L) {
                downstream.onNext(NotificationLite.<T>getValue(o));
                if (r != Long.MAX_VALUE) {
                    decrementAndGet();
                }
                return false;
            }
            cancel();
            downstream.onError(new MissingBackpressureException("Could not deliver value due to lack of requests"));
            return true;
        }

        void emitLoop() {
            for (;;) {
                if (cancelled) {
                    return;
                }
                AppendOnlyLinkedArrayList<Object> q;
                synchronized (this) {
                    q = queue;
                    if (q == null) {
                        emitting = false;
                        return;
                    }
                    queue = null;
                }

                q.forEachWhile(this);
            }
        }

        public boolean isFull() {
            return get() == 0L;
        }
    }
}