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Merged
merged 2 commits into from
Jul 30, 2014
Merged

Amb + Backpressure #1533

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22a56d0
Amb with backpressure support
zsxwing Jul 25, 2014
c880788
Propagate request(n) to each AmbSubscriber
benjchristensen Jul 30, 2014
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121 changes: 92 additions & 29 deletions rxjava-core/src/main/java/rx/internal/operators/OnSubscribeAmb.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,12 +16,17 @@
package rx.internal.operators;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicReference;

import rx.Observable;
import rx.Observable.OnSubscribe;
import rx.Producer;
import rx.Subscriber;
import rx.functions.Action0;
import rx.subscriptions.Subscriptions;

/**
* Given multiple {@link Observable}s, propagates the one that first emits an item.
Expand Down Expand Up @@ -262,22 +267,23 @@ public static <T> OnSubscribe<T> amb(final Iterable<? extends Observable<? exten

private static final class AmbSubscriber<T> extends Subscriber<T> {

private static final int NONE = -1;

private final Subscriber<? super T> subscriber;
private final int index;
private final AtomicInteger choice;
private final Selection<T> selection;

private AmbSubscriber(Subscriber<? super T> subscriber, int index, AtomicInteger choice) {
private AmbSubscriber(long requested, Subscriber<? super T> subscriber, Selection<T> selection) {
this.subscriber = subscriber;
this.choice = choice;
this.index = index;
this.selection = selection;
// initial request
request(requested);
}

private final void requestMore(long n) {
request(n);
}

@Override
public void onNext(T args) {
if (!isSelected()) {
unsubscribe();
return;
}
subscriber.onNext(args);
Expand All @@ -286,7 +292,6 @@ public void onNext(T args) {
@Override
public void onCompleted() {
if (!isSelected()) {
unsubscribe();
return;
}
subscriber.onCompleted();
Expand All @@ -295,44 +300,102 @@ public void onCompleted() {
@Override
public void onError(Throwable e) {
if (!isSelected()) {
unsubscribe();
return;
}
subscriber.onError(e);
}

private boolean isSelected() {
int ch = choice.get();
if (ch == NONE) {
return choice.compareAndSet(NONE, index);
if (selection.choice.get() == this) {
// fast-path
return true;
} else {
if (selection.choice.compareAndSet(null, this)) {
selection.unsubscribeOthers(this);
return true;
} else {
// we lost so unsubscribe ... and force cleanup again due to possible race conditions
selection.unsubscribeLosers();
return false;
}
}
}
}

private static class Selection<T> {
final AtomicReference<AmbSubscriber<T>> choice = new AtomicReference<AmbSubscriber<T>>();
final Collection<AmbSubscriber<T>> ambSubscribers = new ConcurrentLinkedQueue<AmbSubscriber<T>>();

public void unsubscribeLosers() {
AmbSubscriber<T> winner = choice.get();
if(winner != null) {
unsubscribeOthers(winner);
}
}

public void unsubscribeOthers(AmbSubscriber<T> notThis) {
for (AmbSubscriber<T> other : ambSubscribers) {
if (other != notThis) {
other.unsubscribe();
}
}
return ch == index;
ambSubscribers.clear();
}

}

private final Iterable<? extends Observable<? extends T>> sources;
private final Selection<T> selection = new Selection<T>();

private OnSubscribeAmb(Iterable<? extends Observable<? extends T>> sources) {
this.sources = sources;
}

@Override
public void call(Subscriber<? super T> subscriber) {
AtomicInteger choice = new AtomicInteger(AmbSubscriber.NONE);
int index = 0;
for (Observable<? extends T> source : sources) {
if (subscriber.isUnsubscribed()) {
break;
public void call(final Subscriber<? super T> subscriber) {
subscriber.add(Subscriptions.create(new Action0() {

@Override
public void call() {
if (selection.choice.get() != null) {
// there is a single winner so we unsubscribe it
selection.choice.get().unsubscribe();
}
// if we are racing with others still existing, we'll also unsubscribe them
if(!selection.ambSubscribers.isEmpty()) {
for (AmbSubscriber<T> other : selection.ambSubscribers) {
other.unsubscribe();
}
selection.ambSubscribers.clear();
}
}
if (choice.get() != AmbSubscriber.NONE) {
// Already choose someone, the rest Observables can be skipped.
break;

}));
subscriber.setProducer(new Producer() {

@Override
public void request(long n) {
if (selection.choice.get() != null) {
// propagate the request to that single Subscriber that won
selection.choice.get().requestMore(n);
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Needs return here.

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Good catch.

} else {
for (Observable<? extends T> source : sources) {
if (subscriber.isUnsubscribed()) {
break;
}
AmbSubscriber<T> ambSubscriber = new AmbSubscriber<T>(n, subscriber, selection);
selection.ambSubscribers.add(ambSubscriber);
// possible race condition in previous lines ... a choice may have been made so double check (instead of synchronizing)
if (selection.choice.get() != null) {
// Already chose one, the rest can be skipped and we can clean up
selection.unsubscribeOthers(selection.choice.get());
break;
}
source.unsafeSubscribe(ambSubscriber);
}
}
}
AmbSubscriber<T> ambSubscriber = new AmbSubscriber<T>(subscriber, index, choice);
subscriber.add(ambSubscriber);
source.unsafeSubscribe(ambSubscriber);
index++;
}
});
}

}
62 changes: 62 additions & 0 deletions rxjava-core/src/test/java/rx/internal/operators/OnSubscribeAmbTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -15,13 +15,15 @@
*/
package rx.internal.operators;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.inOrder;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.times;
import static rx.internal.operators.OnSubscribeAmb.amb;

import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

import org.junit.Before;
import org.junit.Test;
Expand All @@ -30,9 +32,13 @@
import rx.Observable;
import rx.Observable.OnSubscribe;
import rx.Observer;
import rx.Producer;
import rx.Scheduler;
import rx.Subscriber;
import rx.functions.Action0;
import rx.internal.util.RxRingBuffer;
import rx.observers.TestSubscriber;
import rx.schedulers.Schedulers;
import rx.schedulers.TestScheduler;
import rx.subscriptions.CompositeSubscription;

Expand Down Expand Up @@ -157,4 +163,60 @@ public void testAmb3() {
inOrder.verifyNoMoreInteractions();
}

@Test
public void testProducerRequestThroughAmb() {
TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
ts.requestMore(3);
final AtomicLong requested1 = new AtomicLong();
final AtomicLong requested2 = new AtomicLong();
Observable<Integer> o1 = Observable.create(new OnSubscribe<Integer>() {

@Override
public void call(Subscriber<? super Integer> s) {
s.setProducer(new Producer() {

@Override
public void request(long n) {
System.out.println("1-requested: " + n);
requested1.set(n);
}

});
}

});
Observable<Integer> o2 = Observable.create(new OnSubscribe<Integer>() {

@Override
public void call(Subscriber<? super Integer> s) {
s.setProducer(new Producer() {

@Override
public void request(long n) {
System.out.println("2-requested: " + n);
requested2.set(n);
}

});
}

});
Observable.amb(o1, o2).subscribe(ts);
assertEquals(3, requested1.get());
assertEquals(3, requested2.get());
}

@Test
public void testBackpressure() {
TestSubscriber<Integer> ts = new TestSubscriber<Integer>();
Observable.range(0, RxRingBuffer.SIZE * 2)
.ambWith(Observable.range(0, RxRingBuffer.SIZE * 2))
.observeOn(Schedulers.computation()) // observeOn has a backpressured RxRingBuffer
.delay(1, TimeUnit.MICROSECONDS) // make it a slightly slow consumer
.subscribe(ts);

ts.awaitTerminalEvent();
ts.assertNoErrors();
assertEquals(RxRingBuffer.SIZE * 2, ts.getOnNextEvents().size());
}
}