/**
* 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 org.reactivestreams.Subscription;
import io.reactivex.FlowableSubscriber;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.EndConsumerHelper;
/**
* Abstract base implementation of a {@link org.reactivestreams.Subscriber Subscriber} with
* support for requesting via {@link #request(long)}, cancelling via
* via {@link #cancel()} (both synchronously) and calls {@link #onStart()}
* when the subscription happens.
*
* <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.
*
* <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>Use the protected {@link #cancel()} to cancel the sequence from within an
* {@code onNext} implementation.
*
* <p>Like all other consumers, {@code DefaultSubscriber} 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.
* @param <T> the value type
*
* <p>Example<pre><code>
* Flowable.range(1, 5)
* .subscribe(new DefaultSubscriber<Integer>() {
* @Override public void onStart() {
* System.out.println("Start!");
* 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!");
* }
* });
* </code></pre>
*/
public abstract class DefaultSubscriber<T> implements FlowableSubscriber<T> {
private Subscription s;
@Override
public final void onSubscribe(Subscription s) {
if (EndConsumerHelper.validate(this.s, s, getClass())) {
this.s = s;
onStart();
}
}
/**
* Requests from the upstream Subscription.
* @param n the request amount, positive
*/
protected final void request(long n) {
Subscription s = this.s;
if (s != null) {
s.request(n);
}
}
/**
* Cancels the upstream's Subscription.
*/
protected final void cancel() {
Subscription s = this.s;
this.s = SubscriptionHelper.CANCELLED;
s.cancel();
}
/**
* Called once the subscription has been set on this observer; override this
* to perform initialization or issue an initial request.
* <p>
* The default implementation requests {@link Long#MAX_VALUE}.
*/
protected void onStart() {
request(Long.MAX_VALUE);
}
}