rx.internal.operators.BlockingOperatorMostRecent Maven / Gradle / Ivy
/**
* 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.*;
import rx.Observable;
import rx.Subscriber;
import rx.exceptions.Exceptions;
/**
* Returns an Iterable that always returns the item most recently emitted by an Observable, or a
* seed value if no item has yet been emitted.
*
* 
*/
public final class BlockingOperatorMostRecent {
private BlockingOperatorMostRecent() {
throw new IllegalStateException("No instances!");
}
/**
* Returns an {@code Iterable} that always returns the item most recently emitted by the {@code Observable}.
*
* @param the value type
* @param source
* the source {@code Observable}
* @param initialValue
* a default item to return from the {@code Iterable} if {@code source} has not yet emitted any
* items
* @return an {@code Iterable} that always returns the item most recently emitted by {@code source}, or
* {@code initialValue} if {@code source} has not yet emitted any items
*/
public static Iterable mostRecent(final Observable source, final T initialValue) {
return new Iterable() {
@SuppressWarnings("unchecked")
@Override
public Iterator iterator() {
MostRecentObserver mostRecentObserver = new MostRecentObserver(initialValue);
/**
* Subscribe instead of unsafeSubscribe since this is the final subscribe in the chain
* since it is for BlockingObservable.
*/
((Observable)source).subscribe(mostRecentObserver);
return mostRecentObserver.getIterable();
}
};
}
static final class MostRecentObserver extends Subscriber {
volatile Object value;
MostRecentObserver(T value) {
this.value = NotificationLite.next(value);
}
@Override
public void onCompleted() {
value = NotificationLite.completed();
}
@Override
public void onError(Throwable e) {
value = NotificationLite.error(e);
}
@Override
public void onNext(T args) {
value = NotificationLite.next(args);
}
/**
* The {@link Iterator} return is not thread safe. In other words don't call {@link Iterator#hasNext()} in one
* thread expect {@link Iterator#next()} called from a different thread to work.
* @return the Iterator instance
*/
public Iterator getIterable() {
return new Iterator() {
/**
* buffer to make sure that the state of the iterator doesn't change between calling hasNext() and next().
*/
private Object buf;
@Override
public boolean hasNext() {
buf = value;
return !NotificationLite.isCompleted(buf);
}
@Override
public T next() {
try {
// if hasNext wasn't called before calling next.
if (buf == null) {
buf = value;
}
if (NotificationLite.isCompleted(buf)) {
throw new NoSuchElementException();
}
if (NotificationLite.isError(buf)) {
throw Exceptions.propagate(NotificationLite.getError(buf));
}
return NotificationLite.getValue(buf);
}
finally {
buf = null;
}
}
@Override
public void remove() {
throw new UnsupportedOperationException("Read only iterator");
}
};
}
}
}