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/*
* 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.rxjava3.core;
import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.disposables.Disposable;
/**
* Provides a mechanism for receiving push-based notification of a valueless completion or an error.
*
* When a {@code CompletableObserver} is subscribed to a {@link CompletableSource} through the {@link CompletableSource#subscribe(CompletableObserver)} method,
* the {@code CompletableSource} calls {@link #onSubscribe(Disposable)} with a {@link Disposable} that allows
* disposing the sequence at any time. A well-behaved
* {@code CompletableSource} will call a {@code CompletableObserver}'s {@link #onError(Throwable)}
* or {@link #onComplete()} method exactly once as they are considered mutually exclusive terminal signals.
*
* Calling the {@code CompletableObserver}'s method must happen in a serialized fashion, that is, they must not
* be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must
* adhere to the following protocol:
*
onSubscribe (onError | onComplete)?
*
* Subscribing a {@code CompletableObserver} to multiple {@code CompletableSource}s is not recommended. If such reuse
* happens, it is the duty of the {@code CompletableObserver} implementation to be ready to receive multiple calls to
* its methods and ensure proper concurrent behavior of its business logic.
*
* Calling {@link #onSubscribe(Disposable)} or {@link #onError(Throwable)} with a
* {@code null} argument is forbidden.
*
* The implementations of the {@code onXXX} methods should avoid throwing runtime exceptions other than the following cases:
*
* - If the argument is {@code null}, the methods can throw a {@code NullPointerException}.
* Note though that RxJava prevents {@code null}s to enter into the flow and thus there is generally no
* need to check for nulls in flows assembled from standard sources and intermediate operators.
*
* - If there is a fatal error (such as {@code VirtualMachineError}).
*
* @since 2.0
*/
public interface CompletableObserver {
/**
* Called once by the {@link Completable} to set a {@link Disposable} on this instance which
* then can be used to cancel the subscription at any time.
* @param d the {@code Disposable} instance to call dispose on for cancellation, not null
*/
void onSubscribe(@NonNull Disposable d);
/**
* Called once the deferred computation completes normally.
*/
void onComplete();
/**
* Called once if the deferred computation 'throws' an exception.
* @param e the exception, not {@code null}.
*/
void onError(@NonNull Throwable e);
}