/**
* 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.subjects;
import io.reactivex.annotations.CheckReturnValue;
import java.lang.reflect.Array;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.*;
import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.util.*;
import io.reactivex.internal.util.AppendOnlyLinkedArrayList.NonThrowingPredicate;
import io.reactivex.plugins.RxJavaPlugins;
/**
* Subject that emits the most recent item it has observed and all subsequent observed items to each subscribed
* {@link Observer}.
* <p>
* <img width="640" height="415" 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 4 events (including "default").
BehaviorSubject<Object> subject = BehaviorSubject.createDefault("default");
subject.subscribe(observer);
subject.onNext("one");
subject.onNext("two");
subject.onNext("three");
// observer will receive the "one", "two" and "three" events, but not "zero"
BehaviorSubject<Object> subject = BehaviorSubject.create();
subject.onNext("zero");
subject.onNext("one");
subject.subscribe(observer);
subject.onNext("two");
subject.onNext("three");
// observer will receive only onComplete
BehaviorSubject<Object> subject = BehaviorSubject.create();
subject.onNext("zero");
subject.onNext("one");
subject.onComplete();
subject.subscribe(observer);
// observer will receive only onError
BehaviorSubject<Object> subject = BehaviorSubject.create();
subject.onNext("zero");
subject.onNext("one");
subject.onError(new RuntimeException("error"));
subject.subscribe(observer);
} </pre>
*
* @param <T>
* the type of item expected to be observed by the Subject
*/
public final class BehaviorSubject<T> extends Subject<T> {
/** An empty array to avoid allocation in getValues(). */
private static final Object[] EMPTY_ARRAY = new Object[0];
final AtomicReference<Object> value;
final AtomicReference<BehaviorDisposable<T>[]> subscribers;
@SuppressWarnings("rawtypes")
static final BehaviorDisposable[] EMPTY = new BehaviorDisposable[0];
@SuppressWarnings("rawtypes")
static final BehaviorDisposable[] TERMINATED = new BehaviorDisposable[0];
final ReadWriteLock lock;
final Lock readLock;
final Lock writeLock;
final AtomicReference<Throwable> terminalEvent;
long index;
/**
* Creates a {@link BehaviorSubject} without a default item.
*
* @param <T>
* the type of item the Subject will emit
* @return the constructed {@link BehaviorSubject}
*/
@CheckReturnValue
public static <T> BehaviorSubject<T> create() {
return new BehaviorSubject<T>();
}
/**
* Creates a {@link BehaviorSubject} that emits the last item it observed and all subsequent items to each
* {@link Observer} that subscribes to it.
*
* @param <T>
* the type of item the Subject will emit
* @param defaultValue
* the item that will be emitted first to any {@link Observer} as long as the
* {@link BehaviorSubject} has not yet observed any items from its source {@code Observable}
* @return the constructed {@link BehaviorSubject}
*/
@CheckReturnValue
public static <T> BehaviorSubject<T> createDefault(T defaultValue) {
return new BehaviorSubject<T>(defaultValue);
}
/**
* Constructs an empty BehaviorSubject.
* @since 2.0
*/
@SuppressWarnings("unchecked")
BehaviorSubject() {
this.lock = new ReentrantReadWriteLock();
this.readLock = lock.readLock();
this.writeLock = lock.writeLock();
this.subscribers = new AtomicReference<BehaviorDisposable<T>[]>(EMPTY);
this.value = new AtomicReference<Object>();
this.terminalEvent = new AtomicReference<Throwable>();
}
/**
* Constructs a BehaviorSubject with the given initial value.
* @param defaultValue the initial value, not null (verified)
* @throws NullPointerException if {@code defaultValue} is null
* @since 2.0
*/
BehaviorSubject(T defaultValue) {
this();
this.value.lazySet(ObjectHelper.requireNonNull(defaultValue, "defaultValue is null"));
}
@Override
protected void subscribeActual(Observer<? super T> observer) {
BehaviorDisposable<T> bs = new BehaviorDisposable<T>(observer, this);
observer.onSubscribe(bs);
if (add(bs)) {
if (bs.cancelled) {
remove(bs);
} else {
bs.emitFirst();
}
} else {
Throwable ex = terminalEvent.get();
if (ex == ExceptionHelper.TERMINATED) {
observer.onComplete();
} else {
observer.onError(ex);
}
}
}
@Override
public void onSubscribe(Disposable s) {
if (terminalEvent.get() != null) {
s.dispose();
}
}
@Override
public void onNext(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;
}
if (terminalEvent.get() != null) {
return;
}
Object o = NotificationLite.next(t);
setCurrent(o);
for (BehaviorDisposable<T> bs : subscribers.get()) {
bs.emitNext(o, index);
}
}
@Override
public void onError(Throwable t) {
if (t == null) {
t = new NullPointerException("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 (BehaviorDisposable<T> bs : terminate(o)) {
bs.emitNext(o, index);
}
}
@Override
public void onComplete() {
if (!terminalEvent.compareAndSet(null, ExceptionHelper.TERMINATED)) {
return;
}
Object o = NotificationLite.complete();
for (BehaviorDisposable<T> bs : terminate(o)) {
bs.emitNext(o, index); // relaxed read okay since this is the only mutator thread
}
}
@Override
public boolean hasObservers() {
return subscribers.get().length != 0;
}
/* test support*/ int subscriberCount() {
return subscribers.get().length;
}
@Override
public Throwable getThrowable() {
Object o = value.get();
if (NotificationLite.isError(o)) {
return NotificationLite.getError(o);
}
return null;
}
/**
* Returns a single value the Subject currently has or null if no such value exists.
* <p>The method is thread-safe.
* @return a single value the Subject currently has or null if no such value exists
*/
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 Subject.
* <p>The method is thread-safe.
* @return the array containing the snapshot of all values of the Subject
*/
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 Subject.
* <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
*/
@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 subject has any value.
* <p>The method is thread-safe.
* @return true if the subject has any value
*/
public boolean hasValue() {
Object o = value.get();
return o != null && !NotificationLite.isComplete(o) && !NotificationLite.isError(o);
}
boolean add(BehaviorDisposable<T> rs) {
for (;;) {
BehaviorDisposable<T>[] a = subscribers.get();
if (a == TERMINATED) {
return false;
}
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 true;
}
}
}
@SuppressWarnings("unchecked")
void remove(BehaviorDisposable<T> rs) {
for (;;) {
BehaviorDisposable<T>[] a = subscribers.get();
if (a == TERMINATED || a == EMPTY) {
return;
}
int len = a.length;
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;
}
}
}
@SuppressWarnings("unchecked")
BehaviorDisposable<T>[] terminate(Object terminalValue) {
BehaviorDisposable<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) {
writeLock.lock();
try {
index++;
value.lazySet(o);
} finally {
writeLock.unlock();
}
}
static final class BehaviorDisposable<T> implements Disposable, NonThrowingPredicate<Object> {
final Observer<? super T> actual;
final BehaviorSubject<T> state;
boolean next;
boolean emitting;
AppendOnlyLinkedArrayList<Object> queue;
boolean fastPath;
volatile boolean cancelled;
long index;
BehaviorDisposable(Observer<? super T> actual, BehaviorSubject<T> state) {
this.actual = 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;
}
Object o;
synchronized (this) {
if (cancelled) {
return;
}
if (next) {
return;
}
BehaviorSubject<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) {
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) {
return cancelled || NotificationLite.accept(o, actual);
}
void emitLoop() {
for (;;) {
if (cancelled) {
return;
}
AppendOnlyLinkedArrayList<Object> q;
synchronized (this) {
q = queue;
if (q == null) {
emitting = false;
return;
}
queue = null;
}
q.forEachWhile(this);
}
}
}
}