BufferProvider.java
/*
* Copyright 2020 The Android Open Source Project
*
* 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 androidx.camera.video.internal;
import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;
import androidx.camera.core.impl.Observable;
import com.google.common.util.concurrent.ListenableFuture;
/**
* BufferProvider provides buffers for writing data.
*
* <p>BufferProvider has {@link State}, it could be either {@link State#ACTIVE} or
* {@link State#INACTIVE}. The state can be fetched directly through {@link #fetchData()} or use
* {@link #addObserver} to receive state changes.
*
* <p>A buffer for writing data can be acquired with {@link #acquireBuffer()}". The buffer can
* only be obtained when the state is {@link State#ACTIVE}. If the state is
* {@link State#INACTIVE}, the {@link #acquireBuffer()} will return a failed
* {@link ListenableFuture} with {@link IllegalStateException}. If the state is transitioned from
* {@link State#ACTIVE} to {@link State#INACTIVE}, the incomplete {@link ListenableFuture} will
* get {@link java.util.concurrent.CancellationException}. Buffer acquisition can be cancelled
* with {@link ListenableFuture#cancel} if acquisition is not yet complete.
*
* @param <T> the buffer data type
*/
@RequiresApi(21) // TODO(b/200306659): Remove and replace with annotation on package-info.java
public interface BufferProvider<T> extends Observable<BufferProvider.State> {
/**
* Acquires a buffer.
*
* <p>A buffer can only be obtained when the state is {@link State#ACTIVE}. If the state is
* {@link State#INACTIVE}, the {@link #acquireBuffer()} will return an failed
* {@link ListenableFuture} with {@link IllegalStateException}. If the state is transitioned
* from {@link State#ACTIVE} to {@link State#INACTIVE}, the incomplete
* {@link ListenableFuture} will get {@link java.util.concurrent.CancellationException}.
* Buffer acquisition can be cancelled with {@link ListenableFuture#cancel} if acquisition
* is not yet complete.
*
* @return a {@link ListenableFuture} to represent the acquisition.
*/
@NonNull
ListenableFuture<T> acquireBuffer();
/** The state of the BufferProvider. */
enum State {
/** The state means it is able to acquire a buffer. */
ACTIVE,
/**
* The state means it is not able to acquire buffer.
*
* <p>The acquisition via {@link #acquireBuffer()} will get a result with
* {@link IllegalStateException}.
*/
INACTIVE,
}
}