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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.observable.extensions;
/**
* Represents a SimpleQueue plus the means and constants for requesting a fusion mode.
* @param the value type returned by the SimpleQueue.poll()
*/
public interface QueueFuseable extends SimpleQueue {
/**
* Returned by the {@link #requestFusion(int)} if the upstream doesn't support
* the requested mode.
*/
int NONE = 0;
/**
* Request a synchronous fusion mode and can be returned by {@link #requestFusion(int)}
* for an accepted mode.
*
* In synchronous fusion, all upstream values are either already available or is generated
* when {@link #poll()} is called synchronously. When the {@link #poll()} returns null,
* that is the indication if a terminated stream.
* In this mode, the upstream won't call the onXXX methods and callers of
* {@link #poll()} should be prepared to catch exceptions. Note that {@link #poll()} has
* to be called sequentially (from within a serializing drain-loop).
*/
int SYNC = 1;
/**
* Request an asynchronous fusion mode and can be returned by {@link #requestFusion(int)}
* for an accepted mode.
*
* In asynchronous fusion, upstream values may become available to {@link #poll()} eventually.
* Upstream signals onError() and onComplete() as usual but onNext may not actually contain
* the upstream value but have {@code null} instead. Downstream should treat such onNext as indication
* that {@link #poll()} can be called. Note that {@link #poll()} has to be called sequentially
* (from within a serializing drain-loop). In addition, callers of {@link #poll()} should be
* prepared to catch exceptions.
*/
int ASYNC = 2;
/**
* Request any of the {@link #SYNC} or {@link #ASYNC} modes.
*/
int ANY = SYNC | ASYNC;
/**
* Used in binary or combination with the other constants as an input to {@link #requestFusion(int)}
* indicating that the {@link #poll()} will be called behind an asynchronous boundary and thus
* may change the non-trivial computation locations attached to the {@link #poll()} chain of
* fused operators.
*
* For example, fusing map() and observeOn() may move the computation of the map's function over to
* the thread run after the observeOn(), which is generally unexpected.
*/
int BOUNDARY = 4;
/**
* Request a fusion mode from the upstream.
*
* This should be called before {@code onSubscribe} returns.
*
* Calling this method multiple times or after {@code onSubscribe} finished is not allowed
* and may result in undefined behavior.
*
* @param mode the requested fusion mode, allowed values are {@link #SYNC}, {@link #ASYNC},
* {@link #ANY} combined with {@link #BOUNDARY} (e.g., {@code requestFusion(SYNC | BOUNDARY)}).
* @return the established fusion mode: {@link #NONE}, {@link #SYNC}, {@link #ASYNC}.
*/
int requestFusion(int mode);
}