LatencyTuner.h

/*
 * Copyright 2017 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.
 */

#ifndef OBOE_LATENCY_TUNER_
#define OBOE_LATENCY_TUNER_

#include <atomic>
#include <cstdint>
#include "oboe/Definitions.h"
#include "oboe/AudioStream.h"

namespace oboe {

class LatencyTuner {
public:

    explicit LatencyTuner(AudioStream &stream);

    explicit LatencyTuner(AudioStream &stream, int32_t maximumBufferSize);

    Result tune();

    void requestReset();

    bool isAtMaximumBufferSize();

    void setMinimumBufferSize(int32_t bufferSize) {
        mMinimumBufferSize = bufferSize;
    }

    int32_t getMinimumBufferSize() const {
        return mMinimumBufferSize;
    }

    void setBufferSizeIncrement(int32_t sizeIncrement) {
        mBufferSizeIncrement = sizeIncrement;
    }

    int32_t getBufferSizeIncrement() const {
        return mBufferSizeIncrement;
    }

private:

    void reset();

    enum class State {
        Idle,
        Active,
        AtMax,
        Unsupported
    } ;

    // arbitrary number of calls to wait before bumping up the latency
    static constexpr int32_t kIdleCount = 8;
    static constexpr int32_t kDefaultNumBursts = 2;

    AudioStream           &mStream;
    State                 mState = State::Idle;
    int32_t               mMaxBufferSize = 0;
    int32_t               mPreviousXRuns = 0;
    int32_t               mIdleCountDown = 0;
    int32_t               mMinimumBufferSize;
    int32_t               mBufferSizeIncrement;
    std::atomic<int32_t>  mLatencyTriggerRequests{0}; // TODO user atomic requester from AAudio
    std::atomic<int32_t>  mLatencyTriggerResponses{0};
};

} // namespace oboe

#endif // OBOE_LATENCY_TUNER_