/**
* Copyright (c) 2016-present, RxJava Contributors.
*
* 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 io.reactivex.subscribers;
import java.util.concurrent.atomic.
AtomicReference;
import org.reactivestreams.
Subscription;
import io.reactivex.
FlowableSubscriber;
import io.reactivex.disposables.
Disposable;
import io.reactivex.internal.subscriptions.
SubscriptionHelper;
import io.reactivex.internal.util.
EndConsumerHelper;
/**
* An abstract Subscriber that allows asynchronous, external cancellation by implementing Disposable.
*
* <p>All pre-implemented final methods are thread-safe.
*
* <p>The default {@link #onStart()} requests Long.MAX_VALUE by default. Override
* the method to request a custom <em>positive</em> amount. Use the protected {@link #request(long)}
* to request more items and {@link #cancel()} to cancel the sequence from within an
* {@code onNext} implementation.
*
* <p>Note that calling {@link #request(long)} from {@link #onStart()} may trigger
* an immediate, asynchronous emission of data to {@link #onNext(Object)}. Make sure
* all initialization happens before the call to {@code request()} in {@code onStart()}.
* Calling {@link #request(long)} inside {@link #onNext(Object)} can happen at any time
* because by design, {@code onNext} calls from upstream are non-reentrant and non-overlapping.
*
* <p>Like all other consumers, {@code DisposableSubscriber} can be subscribed only once.
* Any subsequent attempt to subscribe it to a new source will yield an
* {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) <class name> multiple times."}.
*
* <p>Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)}
* and {@link #onComplete()} are not allowed to throw any unchecked exceptions.
* If for some reason this can't be avoided, use {@link io.reactivex.Flowable#safeSubscribe(org.reactivestreams.Subscriber)}
* instead of the standard {@code subscribe()} method.
*
* <p>Example<pre><code>
* Disposable d =
* Flowable.range(1, 5)
* .subscribeWith(new DisposableSubscriber<Integer>() {
* @Override public void onStart() {
* request(1);
* }
* @Override public void onNext(Integer t) {
* if (t == 3) {
* cancel();
* }
* System.out.println(t);
* request(1);
* }
* @Override public void onError(Throwable t) {
* t.printStackTrace();
* }
* @Override public void onComplete() {
* System.out.println("Done!");
* }
* });
* // ...
* d.dispose();
* </code></pre>
* @param <T> the received value type.
*/
public abstract class
DisposableSubscriber<T> implements
FlowableSubscriber<T>,
Disposable {
final
AtomicReference<
Subscription>
upstream = new
AtomicReference<
Subscription>();
@
Override
public final void
onSubscribe(
Subscription s) {
if (
EndConsumerHelper.
setOnce(this.
upstream,
s,
getClass())) {
onStart();
}
}
/**
* Called once the single upstream Subscription is set via onSubscribe.
*/
protected void
onStart() {
upstream.
get().
request(
Long.
MAX_VALUE);
}
/**
* Requests the specified amount from the upstream if its Subscription is set via
* onSubscribe already.
* <p>Note that calling this method before a Subscription is set via onSubscribe
* leads to NullPointerException and meant to be called from inside onStart or
* onNext.
* @param n the request amount, positive
*/
protected final void
request(long
n) {
upstream.
get().
request(
n);
}
/**
* Cancels the Subscription set via onSubscribe or makes sure a
* Subscription set asynchronously (later) is cancelled immediately.
* <p>This method is thread-safe and can be exposed as a public API.
*/
protected final void
cancel() {
dispose();
}
@
Override
public final boolean
isDisposed() {
return
upstream.
get() ==
SubscriptionHelper.
CANCELLED;
}
@
Override
public final void
dispose() {
SubscriptionHelper.
cancel(
upstream);
}
}