/**
* 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 com.jakewharton.rxrelay3;
import com.jakewharton.rxrelay3.AppendOnlyLinkedArrayList.NonThrowingPredicate;
import io.reactivex.rxjava3.core.Observer;
import io.reactivex.rxjava3.annotations.CheckReturnValue;
import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.annotations.Nullable;
import io.reactivex.rxjava3.disposables.Disposable;
import java.lang.reflect.Array;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Relay that emits the most recent item it has observed and all subsequent observed items to each subscribed
* {@link Observer}.
* <p>
* <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/S.BehaviorSubject.png" alt="">
* <p>
* Example usage:
* <p>
* <pre> {@code
// observer will receive all events.
BehaviorRelay<Object> subject = BehaviorRelay.createDefault("default");
subject.subscribe(observer);
subject.accept("one");
subject.accept("two");
subject.accept("three");
// observer will receive the "one", "two" and "three" events, but not "zero"
BehaviorRelay<Object> subject = BehaviorRelay.createDefault("default");
subject.accept("zero");
subject.accept("one");
subject.subscribe(observer);
subject.accept("two");
subject.accept("three");
} </pre>
*/
public final class BehaviorRelay<T> extends Relay<T> {
/** An empty array to avoid allocation in getValues(). */
private static final Object[] EMPTY_ARRAY = new Object[0];
final AtomicReference<T> value;
final AtomicReference<BehaviorDisposable<T>[]> subscribers;
@SuppressWarnings("rawtypes")
static final BehaviorDisposable[] EMPTY = new BehaviorDisposable[0];
final Lock readLock;
final Lock writeLock;
long index;
/**
* Creates a {@link BehaviorRelay} without a default item.
*/
@CheckReturnValue
@NonNull
public static <T> BehaviorRelay<T> create() {
return new BehaviorRelay<T>();
}
/**
* Creates a {@link BehaviorRelay} that emits the last item it observed and all subsequent items to each
* {@link Observer} that subscribes to it.
*
* @param defaultValue
* the item that will be emitted first to any {@link Observer} as long as the
* {@link BehaviorRelay} has not yet observed any items from its source {@code Observable}
*/
@CheckReturnValue
@NonNull
public static <T> BehaviorRelay<T> createDefault(T defaultValue) {
return new BehaviorRelay<T>(defaultValue);
}
/**
* Constructs an empty BehaviorRelay.
*/
@SuppressWarnings("unchecked")
BehaviorRelay() {
ReadWriteLock lock = new ReentrantReadWriteLock();
this.readLock = lock.readLock();
this.writeLock = lock.writeLock();
this.subscribers = new AtomicReference<BehaviorDisposable<T>[]>(EMPTY);
this.value = new AtomicReference<T>();
}
/**
* Constructs a BehaviorRelay with the given initial value.
* @param defaultValue the initial value, not null (verified)
* @throws NullPointerException if {@code defaultValue} is null
*/
BehaviorRelay(T defaultValue) {
this();
if (defaultValue == null) throw new NullPointerException("defaultValue == null");
value.lazySet(defaultValue);
}
@Override
protected void subscribeActual(Observer<? super T> observer) {
BehaviorDisposable<T> bs = new BehaviorDisposable<T>(observer, this);
observer.onSubscribe(bs);
add(bs);
if (bs.cancelled) {
remove(bs);
} else {
bs.emitFirst();
}
}
@Override
public void accept(T value) {
if (value == null) throw new NullPointerException("value == null");
setCurrent(value);
for (BehaviorDisposable<T> bs : subscribers.get()) {
bs.emitNext(value, index);
}
}
@Override
public boolean hasObservers() {
return subscribers.get().length != 0;
}
/* test support*/ int subscriberCount() {
return subscribers.get().length;
}
/**
* Returns a single value the Relay currently has or null if no such value exists.
* <p>The method is thread-safe.
*/
@Nullable
public T getValue() {
return value.get();
}
/**
* Returns an Object array containing snapshot all values of the Relay.
* <p>The method is thread-safe.
* @deprecated in 2.1; 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 Relay.
* <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
* @deprecated in 2.1; put the result of {@link #getValue()} into an array manually, will be removed in 3.x
*/
@Deprecated
@SuppressWarnings("unchecked")
public T[] getValues(T[] array) {
T o = value.get();
if (o == null) {
if (array.length != 0) {
array[0] = null;
}
return array;
}
if (array.length != 0) {
array[0] = o;
if (array.length != 1) {
array[1] = null;
}
} else {
array = (T[]) Array.newInstance(array.getClass().getComponentType(), 1);
array[0] = o;
}
return array;
}
/**
* Returns true if the subject has any value.
* <p>The method is thread-safe.
* @return true if the subject has any value
*/
public boolean hasValue() {
return value.get() != null;
}
void add(BehaviorDisposable<T> rs) {
for (;;) {
BehaviorDisposable<T>[] a = subscribers.get();
int len = a.length;
@SuppressWarnings("unchecked")
BehaviorDisposable<T>[] b = new BehaviorDisposable[len + 1];
System.arraycopy(a, 0, b, 0, len);
b[len] = rs;
if (subscribers.compareAndSet(a, b)) {
return;
}
}
}
@SuppressWarnings("unchecked")
void remove(BehaviorDisposable<T> rs) {
for (;;) {
BehaviorDisposable<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;
}
BehaviorDisposable<T>[] b;
if (len == 1) {
b = EMPTY;
} else {
b = new BehaviorDisposable[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;
}
}
}
void setCurrent(T o) {
writeLock.lock();
index++;
value.lazySet(o);
writeLock.unlock();
}
static final class BehaviorDisposable<T> implements Disposable, NonThrowingPredicate<T> {
final Observer<? super T> downstream;
final BehaviorRelay<T> state;
boolean next;
boolean emitting;
AppendOnlyLinkedArrayList<T> queue;
boolean fastPath;
volatile boolean cancelled;
long index;
BehaviorDisposable(Observer<? super T> actual, BehaviorRelay<T> state) {
this.downstream = actual;
this.state = state;
}
@Override
public void dispose() {
if (!cancelled) {
cancelled = true;
state.remove(this);
}
}
@Override
public boolean isDisposed() {
return cancelled;
}
void emitFirst() {
if (cancelled) {
return;
}
T o;
synchronized (this) {
if (cancelled) {
return;
}
if (next) {
return;
}
BehaviorRelay<T> s = state;
Lock lock = s.readLock;
lock.lock();
index = s.index;
o = s.value.get();
lock.unlock();
emitting = o != null;
next = true;
}
if (o != null) {
test(o);
emitLoop();
}
}
void emitNext(T value, long stateIndex) {
if (cancelled) {
return;
}
if (!fastPath) {
synchronized (this) {
if (cancelled) {
return;
}
if (index == stateIndex) {
return;
}
if (emitting) {
AppendOnlyLinkedArrayList<T> q = queue;
if (q == null) {
q = new AppendOnlyLinkedArrayList<T>(4);
queue = q;
}
q.add(value);
return;
}
next = true;
}
fastPath = true;
}
test(value);
}
@Override
public boolean test(T o) {
if (!cancelled) {
downstream.onNext(o);
}
return false;
}
void emitLoop() {
for (;;) {
if (cancelled) {
return;
}
AppendOnlyLinkedArrayList<T> q;
synchronized (this) {
q = queue;
if (q == null) {
emitting = false;
return;
}
queue = null;
}
q.forEachWhile(this);
}
}
}
}
