apps/OboeTester/app/src/main/cpp/OboeStreamCallbackProxy.cpp

/*
 * 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.
 */

#include "common/OboeDebug.h"
#include "OboeStreamCallbackProxy.h"

// Linear congruential random number generator.
static uint32_t s_random16() {
    static uint32_t seed = 1234;
    seed = ((seed * 31421) + 6927) & 0x0FFFF;
    return seed;
}

/**
 * The random number generator is good for burning CPU because the compiler cannot
 * easily optimize away the computation.
 * @param workload number of times to execute the loop
 * @return a white noise value between -1.0 and +1.0
 */
static float s_burnCPU(int32_t workload) {
    uint32_t random = 0;
    for (int32_t i = 0; i < workload; i++) {
        for (int32_t j = 0; j < 10; j++) {
            random = random ^ s_random16();
        }
    }
    return (random - 32768) * (1.0 / 32768);
}

bool OboeStreamCallbackProxy::mCallbackReturnStop = false;

int64_t OboeStreamCallbackProxy::getNanoseconds(clockid_t clockId) {
    struct timespec time;
    int result = clock_gettime(clockId, &time);
    if (result < 0) {
        return result;
    }
    return (time.tv_sec * 1e9) + time.tv_nsec;
}

oboe::DataCallbackResult OboeStreamCallbackProxy::onAudioReady(
        oboe::AudioStream *audioStream,
        void *audioData,
        int numFrames) {
    oboe::DataCallbackResult callbackResult = oboe::DataCallbackResult::Stop;
    int64_t startTimeNanos = getNanoseconds();

    mCallbackCount++;
    mFramesPerCallback = numFrames;

    if (mCallbackReturnStop) {
        return oboe::DataCallbackResult::Stop;
    }

    s_burnCPU((int32_t)(mWorkload * kWorkloadScaler * numFrames));

    if (mCallback != nullptr) {
        callbackResult = mCallback->onAudioReady(audioStream, audioData, numFrames);
    }

    // Update CPU load
    double calculationTime = (double)(getNanoseconds() - startTimeNanos);
    double inverseRealTime = audioStream->getSampleRate() / (1.0e9 * numFrames);
    double currentCpuLoad = calculationTime * inverseRealTime; // avoid a divide
    mCpuLoad = (mCpuLoad * 0.95) + (currentCpuLoad * 0.05); // simple low pass filter

    return callbackResult;
}