com.jakewharton.rxrelay2.BehaviorRelay Maven / Gradle / Ivy
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/**
* Copyright 2016 Netflix, Inc.
*
* 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.rxrelay2;
import com.jakewharton.rxrelay2.AppendOnlyLinkedArrayList.NonThrowingPredicate;
import io.reactivex.Observer;
import io.reactivex.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}.
*
* 
*
* Example usage:
*
*
{@code
// observer will receive all events.
BehaviorRelay
*/
public final class BehaviorRelay extends Relay {
/** An empty array to avoid allocation in getValues(). */
private static final Object[] EMPTY_ARRAY = new Object[0];
final AtomicReference value;
private final AtomicReference[]> subscribers;
@SuppressWarnings("rawtypes")
private static final BehaviorDisposable[] EMPTY = new BehaviorDisposable[0];
final Lock readLock;
private final Lock writeLock;
long index;
/**
* Creates a {@link BehaviorRelay} without a default item.
*/
public static BehaviorRelay create() {
return new BehaviorRelay();
}
/**
* 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}
*/
public static BehaviorRelay createDefault(T defaultValue) {
return new BehaviorRelay(defaultValue);
}
/**
* Constructs an empty BehaviorRelay.
*/
@SuppressWarnings("unchecked") private BehaviorRelay() {
ReadWriteLock lock = new ReentrantReadWriteLock();
this.readLock = lock.readLock();
this.writeLock = lock.writeLock();
this.subscribers = new AtomicReference[]>(EMPTY);
this.value = new AtomicReference();
}
/**
* Constructs a BehaviorRelay with the given initial value.
* @param defaultValue the initial value, not null (verified)
* @throws NullPointerException if {@code defaultValue} is null
*/
private BehaviorRelay(T defaultValue) {
this();
if (defaultValue == null) throw new NullPointerException("defaultValue == null");
value.lazySet(defaultValue);
}
@Override
protected void subscribeActual(Observer observer) {
BehaviorDisposable bs = new BehaviorDisposable(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 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.
* The method is thread-safe.
*/
public T getValue() {
return value.get();
}
/**
* Returns an Object array containing snapshot all values of the Relay.
*
The method is thread-safe.
*/
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.
*
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.
* @param array the target array to copy values into if it fits
*/
@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.
*
The method is thread-safe.
* @return true if the subject has any value
*/
public boolean hasValue() {
return value.get() != null;
}
private void add(BehaviorDisposable rs) {
for (;;) {
BehaviorDisposable[] a = subscribers.get();
int len = a.length;
@SuppressWarnings("unchecked")
BehaviorDisposable[] 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 rs) {
for (;;) {
BehaviorDisposable[] a = subscribers.get();
if (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[] 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;
}
}
}
private void setCurrent(T current) {
writeLock.lock();
try {
index++;
value.lazySet(current);
} finally {
writeLock.unlock();
}
}
static final class BehaviorDisposable implements Disposable, NonThrowingPredicate {
final Observer actual;
final BehaviorRelay state;
boolean next;
boolean emitting;
AppendOnlyLinkedArrayList queue;
boolean fastPath;
volatile boolean cancelled;
long index;
BehaviorDisposable(Observer actual, BehaviorRelay 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;
}
T o;
synchronized (this) {
if (cancelled) {
return;
}
if (next) {
return;
}
BehaviorRelay 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 q = queue;
if (q == null) {
q = new AppendOnlyLinkedArrayList(4);
queue = q;
}
q.add(value);
return;
}
next = true;
}
fastPath = true;
}
test(value);
}
@Override
public boolean test(T o) {
if (!cancelled) {
actual.onNext(o);
}
return false;
}
void emitLoop() {
for (;;) {
if (cancelled) {
return;
}
AppendOnlyLinkedArrayList q;
synchronized (this) {
q = queue;
if (q == null) {
emitting = false;
return;
}
queue = null;
}
q.forEachWhile(this);
}
}
}
}