rx.internal.operators.BlockingOperatorToFuture 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.concurrent.*;
import java.util.concurrent.atomic.AtomicReference;
import rx.*;
/**
* Returns a Future representing the single value emitted by an Observable.
*
* 
*
* The toFuture operation throws an exception if the Observable emits more than one item. If the
* Observable may emit more than item, use toList().toFuture().
*/
public final class BlockingOperatorToFuture {
private BlockingOperatorToFuture() {
throw new IllegalStateException("No instances!");
}
/**
* Returns a Future that expects a single item from the observable.
*
* @param that
* an observable sequence to get a Future for.
* @param
* the type of source.
* @return the Future to retrieve a single elements from an Observable
*/
public static Future toFuture(Observable that) {
final CountDownLatch finished = new CountDownLatch(1);
final AtomicReference value = new AtomicReference();
final AtomicReference error = new AtomicReference();
@SuppressWarnings("unchecked")
final Subscription s = ((Observable)that).single().subscribe(new Subscriber() {
@Override
public void onCompleted() {
finished.countDown();
}
@Override
public void onError(Throwable e) {
error.compareAndSet(null, e);
finished.countDown();
}
@Override
public void onNext(T v) {
// "single" guarantees there is only one "onNext"
value.set(v);
}
});
return new Future() {
private volatile boolean cancelled;
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
if (finished.getCount() > 0) {
cancelled = true;
s.unsubscribe();
// release the latch (a race condition may have already released it by now)
finished.countDown();
return true;
} else {
// can't cancel
return false;
}
}
@Override
public boolean isCancelled() {
return cancelled;
}
@Override
public boolean isDone() {
return finished.getCount() == 0;
}
@Override
public T get() throws InterruptedException, ExecutionException {
finished.await();
return getValue();
}
@Override
public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
if (finished.await(timeout, unit)) {
return getValue();
} else {
throw new TimeoutException("Timed out after " + unit.toMillis(timeout) + "ms waiting for underlying Observable.");
}
}
private T getValue() throws ExecutionException {
final Throwable throwable = error.get();
if (throwable != null) {
throw new ExecutionException("Observable onError", throwable);
} else if (cancelled) {
// Contract of Future.get() requires us to throw this:
throw new CancellationException("Subscription unsubscribed");
} else {
return value.get();
}
}
};
}
}