Android 服务中的数据并发与传感器数据

Question

我的应用程序是运行一个 Service，它与多传感器腕带保持 BLE 连接。 Service 实现了腕带 SDK 的一些回调方法，每秒钟调用几次新数据。

我想将来自不同传感器的这些数据放在同一个 Observation 对象中，并与其时间戳相关。所有 Observation 个对象每 60 秒被推送到后端服务器，传感器数据被放在一起以减少发送这些 Observation 个对象的开销。

下面的代码片段介绍了我现在正在做的事情。我的问题是 observationFetcher 中的 while 循环完全阻止了应用程序。是否有任何其他方法可以在不使用块 while 循环的情况下同步这些传感器数据？

    observationFetcher = new Runnable() {
        @Override
        public void run() {
            while (isRecording) {
                if (lastMillis != currentMillis) {
                    Observation obs = sm.getValues();
                    obs.setPropertyAsString("gateway.id", UUID);
                    observations.add(obs);
                    lastMillis = currentMillis;
                }
            }
        }
    };

public void didReceiveGSR(float gsr, double timestamp) {
    long t = System.currentTimeMillis() / 1000;

    sm.setGsrValue(t, gsr);
    currentMillis = t;
}

public void didReceiveIBI(float ibi, double timestamp) {
    sm.setIbiValue(ibi);
}

sm 是一个具有 synchronized 方法的对象，用于将同一秒内的所有传感器数据放在一起。

Answer 1

如果我错了请纠正我，但我看不出有理由浪费 CPU 时间无限迭代。当然，我没有看到完整的代码，你的 API 可能不允许你做一些事情，但我会按以下方式实现数据处理：

final class Observation {
    private float gsr;
    private float ibi;

    public Observation(float gsr, float ibi) {
        this.gsr = gsr;
        this.ibi = ibi;
    }

    // getters & setters

}

public final class Observations {
    private final ConcurrentHashMap<Long, Observation> observations = new ConcurrentHashMap<>();

    public void insertGsrValue(long timestamp, float gsr) {
        for (;;) {
            Observation observation = observations.get(timestamp);
            if (observation == null) {
                observation = observations.putIfAbsent(timestamp, new Observation(gsr, 0.0f));
                if (observation == null) {
                    return;
                }
            }
            if (observations.replace(timestamp, observation, new Observation(gsr, observation.getIbi()))) {
                return;
            }
        }
    }

    public void insertIbiValue(long timestamp, float ibi) {
        for (;;) {
            Observation observation = observations.get(timestamp);
            if (observation == null) {
                observation = observations.putIfAbsent(timestamp, new Observation(0.0f, ibi));
                if (observation == null) {
                    return;
                }
            }
            if (observations.replace(timestamp, observation, new Observation(observation.getGsr(), ibi))) {
                return;
            }
        }
    }

    public List<Observation> getObservations() {
        return new ArrayList<>(observations.values());
    }

    public void clear() {
        observations.clear();
    }

}

public final class ObservationService extends Service {
    private final Observations observations = new Observations();
    private volatile long currentMillis;
    private HandlerThread handlerThread;
    private Handler handler;

    @Override
    public void onCreate() {
        super.onCreate();
        handlerThread = new HandlerThread("observations_sender_thread");
        handlerThread.start();
        handler = new Handler(handlerThread.getLooper());
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                sendData();
                handler.postDelayed(this, TimeUnit.SECONDS.toMillis(60));
            }
        }, TimeUnit.SECONDS.toMillis(60));
    }

    @Override
    public void onDestroy() {
        handlerThread.quit();
    }

    private void sendData() {
        List<Observation> observationList = observations.getObservations();
        observations.clear();
        // send observation list somehow
    }

    public void didReceiveGSR(float gsr, double timestamp) {
        // assuming this is called on a worker thread
        long t = System.currentTimeMillis() / 1000;
        observations.insertGsrValue(t, gsr);
        currentMillis = t;
    }

    public void didReceiveIBI(float ibi, double timestamp) {
        // assuming this is called on a worker thread
        observations.insertIbiValue(currentMillis, ibi);
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

所以这段代码所做的是将来自传感器的新值插入到哈希映射中，并每 60 秒将其发送到某个地方。这段代码仍然不完美，因为存在并发问题。例如，如果先有 2 个 gsr 值，然后有一个 ibi 值，那么我们将丢失第一个 gsr 值。

无论如何，这段代码应该让您了解如何避免阻塞线程并存储数据并发。

如果您对代码有任何疑问，请告诉我。

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