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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.*;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.functions.*;
/**
* Abstraction over an RxJava {@link SingleObserver} that allows associating
* a resource with it.
*
* All methods are safe to call from multiple threads, but note that there is no guarantee
* whose terminal event will win and get delivered to the downstream.
*
* Calling {@link #onSuccess(Object)} multiple times has no effect.
* Calling {@link #onError(Throwable)} multiple times or after {@code onSuccess} will route the
* exception into the global error handler via {@link io.reactivex.rxjava3.plugins.RxJavaPlugins#onError(Throwable)}.
*
* The emitter allows the registration of a single resource, in the form of a {@link Disposable}
* or {@link Cancellable} via {@link #setDisposable(Disposable)} or {@link #setCancellable(Cancellable)}
* respectively. The emitter implementations will dispose/cancel this instance when the
* downstream cancels the flow or after the event generator logic calls {@link #onSuccess(Object)},
* {@link #onError(Throwable)}, or when {@link #tryOnError(Throwable)} succeeds.
*
* Only one {@code Disposable} or {@code Cancellable} object can be associated with the emitter at
* a time. Calling either {@code set} method will dispose/cancel any previous object. If there
* is a need for handling multiple resources, one can create a {@link io.reactivex.rxjava3.disposables.CompositeDisposable}
* and associate that with the emitter instead.
*
* The {@link Cancellable} is logically equivalent to {@code Disposable} but allows using cleanup logic that can
* throw a checked exception (such as many {@code close()} methods on Java IO components). Since
* the release of resources happens after the terminal events have been delivered or the sequence gets
* cancelled, exceptions throw within {@code Cancellable} are routed to the global error handler via
* {@link io.reactivex.rxjava3.plugins.RxJavaPlugins#onError(Throwable)}.
*
* @param the value type to emit
*/
public interface SingleEmitter<@NonNull T> {
/**
* Signal a success value.
* @param t the value, not null
*/
void onSuccess(@NonNull T t);
/**
* Signal an exception.
* @param t the exception, not {@code null}
*/
void onError(@NonNull Throwable t);
/**
* Sets a {@link Disposable} on this emitter; any previous {@code Disposable}
* or {@link Cancellable} will be disposed/cancelled.
* This method is thread-safe.
* @param d the {@code Disposable}, {@code null} is allowed
*/
void setDisposable(@Nullable Disposable d);
/**
* Sets a Cancellable on this emitter; any previous {@link Disposable}
* or {@link Cancellable} will be disposed/cancelled.
*
This method is thread-safe.
* @param c the {@code Cancellable} resource, {@code null} is allowed
*/
void setCancellable(@Nullable Cancellable c);
/**
* Returns true if the downstream disposed the sequence or the
* emitter was terminated via {@link #onSuccess(Object)}, {@link #onError(Throwable)},
* or a successful {@link #tryOnError(Throwable)}.
*
This method is thread-safe.
* @return true if the downstream disposed the sequence or the emitter was terminated
*/
boolean isDisposed();
/**
* Attempts to emit the specified {@link Throwable} error if the downstream
* hasn't cancelled the sequence or is otherwise terminated, returning false
* if the emission is not allowed to happen due to lifecycle restrictions.
*
* Unlike {@link #onError(Throwable)}, the {@link io.reactivex.rxjava3.plugins.RxJavaPlugins#onError(Throwable) RxjavaPlugins.onError}
* is not called if the error could not be delivered.
*
History: 2.1.1 - experimental
* @param t the throwable error to signal if possible
* @return true if successful, false if the downstream is not able to accept further
* events
* @since 2.2
*/
boolean tryOnError(@NonNull Throwable t);
}