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Amb with backpressure support #1516

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Amb with backpressure support #1516

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32 changes: 31 additions & 1 deletion 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 @@ -21,6 +21,7 @@

import rx.Observable;
import rx.Observable.OnSubscribe;
import rx.Producer;
import rx.Subscriber;

/**
Expand Down Expand Up @@ -274,6 +275,10 @@ private AmbSubscriber(Subscriber<? super T> subscriber, int index, AtomicInteger
this.index = index;
}

public void requestMore(long n) {
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By default this Subscriber will request Long.MAX_VALUE up, since it doesn't do anything onStart. When I put printlns in the test, it shows how it gets a Long.MAX_VALUE request first:

1-requested: 9223372036854775807
2-requested: 9223372036854775807
requestMore: 3
1-requested: 3
requestMore: 3
2-requested: 3

request(n);
}

@Override
public void onNext(T args) {
if (!isSelected()) {
Expand Down Expand Up @@ -318,7 +323,8 @@ private OnSubscribeAmb(Iterable<? extends Observable<? extends T>> sources) {

@Override
public void call(Subscriber<? super T> subscriber) {
AtomicInteger choice = new AtomicInteger(AmbSubscriber.NONE);
final AtomicInteger choice = new AtomicInteger(AmbSubscriber.NONE);
final List<AmbSubscriber<T>> ambSubscribers = new ArrayList<AmbSubscriber<T>>();
int index = 0;
for (Observable<? extends T> source : sources) {
if (subscriber.isUnsubscribed()) {
Expand All @@ -329,10 +335,34 @@ public void call(Subscriber<? super T> subscriber) {
break;
}
AmbSubscriber<T> ambSubscriber = new AmbSubscriber<T>(subscriber, index, choice);
ambSubscribers.add(ambSubscriber);
subscriber.add(ambSubscriber);
source.unsafeSubscribe(ambSubscriber);
index++;
}
// setProducer at the end so that `ambSubscribers` can be finalized before `subscriber` calls `request`
subscriber.setProducer(new Producer() {

private volatile AmbSubscriber<T> selectedAmbSubscriber;

@Override
public void request(long n) {
if (choice.get() == AmbSubscriber.NONE) {
for (AmbSubscriber<T> ambSubscriber : ambSubscribers) {
// Once one Observable emits a message, `unsubscribe` of other Observables will be called
// and further messages will be dropped. Therefore, requesting all sources won't cause
// the backpressure issue.
ambSubscriber.requestMore(n);
}
}
else {
if (selectedAmbSubscriber == null) {
selectedAmbSubscriber = ambSubscribers.get(choice.get());
}
selectedAmbSubscriber.requestMore(n);
}
}
});
}

}
44 changes: 44 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 +32,11 @@
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.observers.TestSubscriber;
import rx.schedulers.TestScheduler;
import rx.subscriptions.CompositeSubscription;

Expand Down Expand Up @@ -157,4 +161,44 @@ 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) {
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) {
requested2.set(n);
}

});
}

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