/**
* 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.subjects;
import java.util.*;
import rx.
Observer;
import rx.exceptions.
Exceptions;
import rx.functions.
Action1;
import rx.internal.operators.
NotificationLite;
import rx.internal.producers.
SingleProducer;
import rx.subjects.
SubjectSubscriptionManager.
SubjectObserver;
/**
* Subject that publishes only the last item observed to each {@link Observer} once the source {@code Observable}
* has completed. The item is cached and published to any {@code Observer}s which subscribe after the source
* has completed. If the source emitted no items, {@code AsyncSubject} completes without emitting anything.
* If the source terminated in an error, current and future subscribers will receive only the error.
* <p>
* <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/S.AsyncSubject.png" alt="">
* <p>
* Example usage:
* <p>
* <pre> {@code
// observer will receive no onNext events because the subject.onCompleted() isn't called.
AsyncSubject<Object> subject = AsyncSubject.create();
subject.subscribe(observer);
subject.onNext("one");
subject.onNext("two");
subject.onNext("three");
// observer will receive "three" as the only onNext event.
AsyncSubject<Object> subject = AsyncSubject.create();
subject.subscribe(observer);
subject.onNext("one");
subject.onNext("two");
subject.onNext("three");
subject.onCompleted();
} </pre>
*
* @param <T>
* the type of item expected to be observed by the Subject
*/
public final class
AsyncSubject<T> extends
Subject<T, T> {
final
SubjectSubscriptionManager<T>
state;
volatile
Object lastValue;
/**
* Creates and returns a new {@code AsyncSubject}.
* @param <T> the result value type
* @return the new {@code AsyncSubject}
*/
public static <T>
AsyncSubject<T>
create() {
final
SubjectSubscriptionManager<T>
state = new
SubjectSubscriptionManager<T>();
state.
onTerminated = new
Action1<
SubjectObserver<T>>() {
@
Override
public void
call(
SubjectObserver<T>
o) {
Object v =
state.
getLatest();
if (
v == null ||
NotificationLite.
isCompleted(
v)) {
o.
onCompleted();
} else
if (
NotificationLite.
isError(
v)) {
o.
onError(
NotificationLite.
getError(
v));
} else {
o.
actual.
setProducer(new
SingleProducer<T>(
o.
actual,
NotificationLite.<T>
getValue(
v)));
}
}
};
return new
AsyncSubject<T>(
state,
state);
}
protected
AsyncSubject(
OnSubscribe<T>
onSubscribe,
SubjectSubscriptionManager<T>
state) {
super(
onSubscribe);
this.
state =
state;
}
@
Override
public void
onCompleted() {
if (
state.
active) {
Object last =
lastValue;
if (
last == null) {
last =
NotificationLite.
completed();
}
for (
SubjectObserver<T>
bo :
state.
terminate(
last)) {
if (
last ==
NotificationLite.
completed()) {
bo.
onCompleted();
} else {
bo.
actual.
setProducer(new
SingleProducer<T>(
bo.
actual,
NotificationLite.<T>
getValue(
last)));
}
}
}
}
@
Override
public void
onError(final
Throwable e) {
if (
state.
active) {
Object n =
NotificationLite.
error(
e);
List<
Throwable>
errors = null;
for (
SubjectObserver<T>
bo :
state.
terminate(
n)) {
try {
bo.
onError(
e);
} catch (
Throwable e2) {
if (
errors == null) {
errors = new
ArrayList<
Throwable>();
}
errors.
add(
e2);
}
}
Exceptions.
throwIfAny(
errors);
}
}
@
Override
public void
onNext(T
v) {
lastValue =
NotificationLite.
next(
v);
}
@
Override
public boolean
hasObservers() {
return
state.
observers().length > 0;
}
/**
* Check if the Subject has a value.
* <p>Use the {@link #getValue()} method to retrieve such a value.
* <p>Note that unless {@link #hasCompleted()} or {@link #hasThrowable()} returns true, the value
* retrieved by {@code getValue()} may get outdated.
* @return true if and only if the subject has some value but not an error
* @since 1.2
*/
public boolean
hasValue() {
Object v =
lastValue;
Object o =
state.
getLatest();
return !
NotificationLite.
isError(
o) &&
NotificationLite.
isNext(
v);
}
/**
* Check if the Subject has terminated with an exception.
* @return true if the subject has received a throwable through {@code onError}.
* @since 1.2
*/
public boolean
hasThrowable() {
Object o =
state.
getLatest();
return
NotificationLite.
isError(
o);
}
/**
* Check if the Subject has terminated normally.
* @return true if the subject completed normally via {@code onCompleted()}
* @since 1.2
*/
public boolean
hasCompleted() {
Object o =
state.
getLatest();
return
o != null && !
NotificationLite.
isError(
o);
}
/**
* Returns the current value of the Subject if there is such a value and
* the subject hasn't terminated with an exception.
* <p>The method can return {@code null} for various reasons. Use {@link #hasValue()}, {@link #hasThrowable()}
* and {@link #hasCompleted()} to determine if such {@code null} is a valid value, there was an
* exception or the Subject terminated without receiving any value.
* @return the current value or {@code null} if the Subject doesn't have a value,
* has terminated with an exception or has an actual {@code null} as a value.
* @since 1.2
*/
public T
getValue() {
Object v =
lastValue;
Object o =
state.
getLatest();
if (!
NotificationLite.
isError(
o) &&
NotificationLite.
isNext(
v)) {
return
NotificationLite.
getValue(
v);
}
return null;
}
/**
* Returns the Throwable that terminated the Subject.
* @return the Throwable that terminated the Subject or {@code null} if the
* subject hasn't terminated yet or it terminated normally.
* @since 1.2
*/
public
Throwable getThrowable() {
Object o =
state.
getLatest();
if (
NotificationLite.
isError(
o)) {
return
NotificationLite.
getError(
o);
}
return null;
}
}