/**
* Copyright 2014 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 rx.internal.operators;
import java.util.BitSet;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import rx.Observable;
import rx.Observable.OnSubscribe;
import rx.Producer;
import rx.Subscriber;
import rx.exceptions.MissingBackpressureException;
import rx.functions.FuncN;
import rx.internal.util.RxRingBuffer;
/**
* Returns an Observable that combines the emissions of multiple source observables. Once each
* source Observable has emitted at least one item, combineLatest emits an item whenever any of
* the source Observables emits an item, by combining the latest emissions from each source
* Observable with a specified function.
* <p>
* <img width="640" src="https://github.com/ReactiveX/RxJava/wiki/images/rx-operators/combineLatest.png" alt="">
*
* @param <T>
* the common basetype of the source values
* @param <R>
* the result type of the combinator function
*/
public final class OnSubscribeCombineLatest<T, R> implements OnSubscribe<R> {
final List<? extends Observable<? extends T>> sources;
final FuncN<? extends R> combinator;
public OnSubscribeCombineLatest(List<? extends Observable<? extends T>> sources, FuncN<? extends R> combinator) {
this.sources = sources;
this.combinator = combinator;
if (sources.size() > 128) {
// For design simplicity this is limited to 128. If more are really needed we'll need to adjust
// the design of how RxRingBuffer is used in the implementation below.
throw new IllegalArgumentException("More than 128 sources to combineLatest is not supported.");
}
}
@Override
public void call(final Subscriber<? super R> child) {
if (sources.isEmpty()) {
child.onCompleted();
return;
}
if (sources.size() == 1) {
child.setProducer(new SingleSourceProducer<T, R>(child, sources.get(0), combinator));
} else {
child.setProducer(new MultiSourceProducer<T, R>(child, sources, combinator));
}
}
/*
* benjchristensen => This implementation uses a buffer enqueue/drain pattern. It could be optimized to have a fast-path to
* skip the buffer and emit directly when no conflict, but that is quite complicated and I don't have the time to attempt it right now.
*/
final static class MultiSourceProducer<T, R> implements Producer {
private final AtomicBoolean started = new AtomicBoolean();
private final AtomicLong requested = new AtomicLong();
private final List<? extends Observable<? extends T>> sources;
private final Subscriber<? super R> child;
private final FuncN<? extends R> combinator;
private final MultiSourceRequestableSubscriber<T, R>[] subscribers;
/* following are guarded by WIP */
private final RxRingBuffer buffer = RxRingBuffer.getSpmcInstance();
private final Object[] collectedValues;
private final BitSet haveValues;
private volatile int haveValuesCount; // does this need to be volatile or is WIP sufficient?
private final BitSet completion;
private volatile int completionCount; // does this need to be volatile or is WIP sufficient?
@SuppressWarnings("unused")
private volatile long counter;
@SuppressWarnings("rawtypes")
private static final AtomicLongFieldUpdater<MultiSourceProducer> WIP = AtomicLongFieldUpdater.newUpdater(MultiSourceProducer.class, "counter");
@SuppressWarnings("unchecked")
public MultiSourceProducer(final Subscriber<? super R> child, final List<? extends Observable<? extends T>> sources, FuncN<? extends R> combinator) {
this.sources = sources;
this.child = child;
this.combinator = combinator;
int n = sources.size();
this.subscribers = new MultiSourceRequestableSubscriber[n];
this.collectedValues = new Object[n];
this.haveValues = new BitSet(n);
this.completion = new BitSet(n);
}
@Override
public void request(long n) {
BackpressureUtils.getAndAddRequest(requested, n);
if (!started.get() && started.compareAndSet(false, true)) {
/*
* NOTE: this logic will ONLY work if we don't have more sources than the size of the buffer.
*
* We would likely need to make an RxRingBuffer that can be sized to [numSources * n] instead
* of the current global default size it has.
*/
int sizePerSubscriber = RxRingBuffer.SIZE / sources.size();
int leftOver = RxRingBuffer.SIZE % sources.size();
for (int i = 0; i < sources.size(); i++) {
Observable<? extends T> o = sources.get(i);
int toRequest = sizePerSubscriber;
if (i == sources.size() - 1) {
toRequest += leftOver;
}
MultiSourceRequestableSubscriber<T, R> s = new MultiSourceRequestableSubscriber<T, R>(i, toRequest, child, this);
subscribers[i] = s;
o.unsafeSubscribe(s);
}
}
tick();
}
/**
* This will only allow one thread at a time to do the work, but ensures via `counter` increment/decrement
* that there is always once who acts on each `tick`. Same concept as used in OperationObserveOn.
*/
void tick() {
if (WIP.getAndIncrement(this) == 0) {
int emitted = 0;
do {
// we only emit if requested > 0
if (requested.get() > 0) {
Object o = buffer.poll();
if (o != null) {
if (buffer.isCompleted(o)) {
child.onCompleted();
} else {
buffer.accept(o, child);
emitted++;
requested.decrementAndGet();
}
}
}
} while (WIP.decrementAndGet(this) > 0);
if (emitted > 0) {
for (MultiSourceRequestableSubscriber<T, R> s : subscribers) {
s.requestUpTo(emitted);
}
}
}
}
public void onCompleted(int index, boolean hadValue) {
if (!hadValue) {
child.onCompleted();
return;
}
boolean done = false;
synchronized (this) {
if (!completion.get(index)) {
completion.set(index);
completionCount++;
done = completionCount == collectedValues.length;
}
}
if (done) {
buffer.onCompleted();
tick();
}
}
/**
* @return boolean true if propagated value
*/
public boolean onNext(int index, T t) {
synchronized (this) {
if (!haveValues.get(index)) {
haveValues.set(index);
haveValuesCount++;
}
collectedValues[index] = t;
if (haveValuesCount != collectedValues.length) {
// haven't received value from each source yet so won't emit
return false;
} else {
try {
buffer.onNext(combinator.call(collectedValues));
} catch (MissingBackpressureException e) {
onError(e);
} catch (Throwable e) {
onError(e);
}
}
}
tick();
return true;
}
public void onError(Throwable e) {
child.onError(e);
}
}
final static class MultiSourceRequestableSubscriber<T, R> extends Subscriber<T> {
final MultiSourceProducer<T, R> producer;
final int index;
final AtomicLong emitted = new AtomicLong();
boolean hasValue = false;
public MultiSourceRequestableSubscriber(int index, int initial, Subscriber<? super R> child, MultiSourceProducer<T, R> producer) {
super(child);
this.index = index;
this.producer = producer;
request(initial);
}
public void requestUpTo(long n) {
do {
long r = emitted.get();
long u = Math.min(r, n);
if (emitted.compareAndSet(r, r - u)) {
request(u);
break;
}
} while (true);
}
@Override
public void onCompleted() {
producer.onCompleted(index, hasValue);
}
@Override
public void onError(Throwable e) {
producer.onError(e);
}
@Override
public void onNext(T t) {
hasValue = true;
emitted.incrementAndGet();
boolean emitted = producer.onNext(index, t);
if (!emitted) {
request(1);
}
}
}
final static class SingleSourceProducer<T, R> implements Producer {
final AtomicBoolean started = new AtomicBoolean();
final Observable<? extends T> source;
final Subscriber<? super R> child;
final FuncN<? extends R> combinator;
final SingleSourceRequestableSubscriber<T, R> subscriber;
public SingleSourceProducer(final Subscriber<? super R> child, Observable<? extends T> source, FuncN<? extends R> combinator) {
this.source = source;
this.child = child;
this.combinator = combinator;
this.subscriber = new SingleSourceRequestableSubscriber<T, R>(child, combinator);
}
@Override
public void request(final long n) {
subscriber.requestMore(n);
if (started.compareAndSet(false, true)) {
source.unsafeSubscribe(subscriber);
}
}
}
final static class SingleSourceRequestableSubscriber<T, R> extends Subscriber<T> {
private final Subscriber<? super R> child;
private final FuncN<? extends R> combinator;
SingleSourceRequestableSubscriber(Subscriber<? super R> child, FuncN<? extends R> combinator) {
super(child);
this.child = child;
this.combinator = combinator;
}
public void requestMore(long n) {
request(n);
}
@Override
public void onNext(T t) {
child.onNext(combinator.call(t));
}
@Override
public void onError(Throwable e) {
child.onError(e);
}
@Override
public void onCompleted() {
child.onCompleted();
}
}
}