Polling service: irregular intervals

Question

I've, for test purpose, a little android app composed by a simple activity where you can insert an host, a port and a interval in second. The app starts a service that creates a thread with a cycle that reads from an input stream of a socket until it is intentionally stopped. Here is the code of the service:

@Override
public int onStartCommand(Intent intent, int flags, int startId) {


    prepareFileLogging();

    FILELOG.info("PollingService: onStartCommand");

    mNotificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    Intent bIntent = new Intent(this, MainActivity.class);
    PendingIntent pbIntent = PendingIntent
            .getActivity(this, 0, bIntent, Intent.FLAG_ACTIVITY_CLEAR_TOP);
    Notification.Builder bBuilder =
            new Notification.Builder(this)
                    .setSmallIcon(android.R.drawable.stat_notify_sync)
                    .setContentTitle("PollingTest")
                    .setContentText("Servizio di polling attivo")
                    .setAutoCancel(true)
                    .setOngoing(true)
                    .setContentIntent(pbIntent);

    this.startForeground(1, bBuilder.build());

    Log.i("PollingService", "Received start id " + startId + ": " + intent);

    FILELOG.info("PollingService: Received start id " + startId + ": " + intent);


    hostName = intent.getExtras().getString(PAR_HOST);
    portNumber = intent.getExtras().getInt(PAR_PORT);
    freqSeconds = intent.getExtras().getInt(PAR_FREQ);


    if(pollingThread == null){

        FILELOG.info("pollingThread not running: starting...");

        pollingThread = new Poll();
        pollingThread.start();


    }



    Toast.makeText(this, "Servizio in Background: ServizioSincronizzazione.onCreate()",
            Toast.LENGTH_LONG).show();

    mReceiver = new BroadcastRec();

    getApplication().registerReceiver(mReceiver, filter);


    return START_REDELIVER_INTENT;

}




@Override
public void onDestroy() {

    mNotificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    Notification.Builder bBuilder = new Notification.Builder(this)
            .setSmallIcon(android.R.drawable.stat_notify_error).setContentTitle(
                    "PollingTest")
            .setContentText("Il Servizio di polling è sinterrotto");

    Toast.makeText(this, "Servizio interrotto", Toast.LENGTH_SHORT).show();

    getApplication().unregisterReceiver(mReceiver);

    stopPollingService();
    Log.i("PollingService", "onDestroy");

    super.onDestroy();
}



private class Poll extends Thread {

    @Override
    public void run() {

        Thread thisThread = Thread.currentThread();

        FILELOG.info("pollingThread: started");

        try {

            Socket echoSocket = new Socket(hostName, portNumber);

            PrintWriter out =
                    new PrintWriter(echoSocket.getOutputStream(), true);
            BufferedReader in =
                    new BufferedReader(
                            new InputStreamReader(echoSocket.getInputStream()));


            int nanos = 250000;

            while (pollingThread == thisThread) {

                Log.i("PollThread", "start of a new call");

                out.println("prova");
                String response = in.readLine();
                FILELOG.info("pollingThread: server response: " +response);

                System.out.println("server: " + response);

                if (response != null && response.equals("null")) {
                    FILELOG.info("pollingThread: server down (reponse 'null'), new socket");

                    echoSocket = new Socket(hostName, portNumber);
                }


                sendBroadcast(new Intent());

                try {
                    Log.i("PollThread", "timeout start...");
                    Thread.sleep(freqSeconds*1000, nanos);
                } catch (InterruptedException e) {
                    Log.i("PollThread", e.getMessage());
                    FILELOG.info("pollingThread error: " + e.getMessage());
                }
            }


        } catch (UnknownHostException e) {
            FILELOG.info("pollingThread error: Don't know about host " + e.getMessage());

            System.err.println("Don't know about host " + hostName);
            stopPollingService();

        } catch (IOException e) {
            FILELOG.info("pollingThread error: Couldn't get I/O for the connection to " + e.getMessage());
            System.err.println("Couldn't get I/O for the connection to " +
                    hostName);
            stopPollingService();


        }


    }
}

I've keep the app running on a tablet for one day analyzing the drain of battery and the intervals between two request to the server. The problem I noticed is that for about 10 minutes the 5 seconds interval is respected, then it changes between 5 and 20 seconds! The tablet has been waked up a couple of times and unlocked and the service never crashed. Here it is the sequence of intervals observed by the server:

Someone can think a reason of why this happened?

Answer 1

The system is most likely going into a low power state because the device is idle for 10 minutes. In order to reliably wake up you would need to either use an alarm via the AlarmManager or hold a partial wake lock.