PARTIAL_WAKE_LOCK and thread running in a service

Question

I have got a service which runs a thread. The thread save some data in a file (in the sdcard). When Android goes to sleep, I need that the service and the thread continue running. I tried it with a PARTIAL_WAKE_LOCK, but it doesn't work; the thread stops while Android is sleeping. Other locks like FULL_WAKE_LOCK works, but I need to use PARTIAL_WAKE_LOCK because, in the future, in that thread I will read from a serial port and I don't care the screen turn off.

I don't know if I have got some mistake in the code, or if I don't understand the PARTIAL_WAKE_LOCK. Somebody can tell me why my solution doesn't wrok?

This is part of the code of the main activity, where the service is stareted:

public void onClick(View v) {
    if (SerialPortService.WAKELOCK == null) {
        PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
        SerialPortService.WAKELOCK = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, SerialPortService.WL_TAG);
        SerialPortService.WAKELOCK.acquire();
        startService(new Intent(getApplicationContext(), SerialPortService.class));
    }
}

This is the code of the service:

public class SerialPortService extends Service {

    public static String WL_TAG = "serial_port_wl_tag";
    public static PowerManager.WakeLock WAKELOCK = null;
    private BufferedWriter out = null;
    private ReadThread readThread;

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

    public void onCreate() {
        super.onCreate();
        try {
            File root = Environment.getExternalStorageDirectory();
            if (root.canWrite()){
                File dataFile = new File(root, "batterytest.txt");
                FileWriter dataFileWritter = new FileWriter(dataFile);
                out = new BufferedWriter(dataFileWritter);
            }
        } catch (IOException ioe) {
            Log.d("TEST", "Could not open file " + ioe.getMessage());
        }
        readThread = new ReadThread();
        readThread.start();
    }

    public void onDestroy() {
        if (readThread != null) readThread.interrupt();
        WAKELOCK.release();
        WAKELOCK = null;
        try {
            out.close();
        } catch (IOException ioe) {
            Log.d("TEST", "Could not close file " + ioe.getMessage());
        }
        super.onDestroy();
    }

    private class ReadThread extends Thread {
        public void run() {
            super.run();
            while (!isInterrupted()) {
                try {
                    Thread.sleep(5000);
                    if (out != null) {
                        Calendar now = Calendar.getInstance();
                        out.write(now.getTime().toString());
                        out.newLine();
                } catch (IOException ioe) {
                    Log.d("TEST", "Could not read file " + ioe.getMessage());}
                    return;
                } catch (InterruptedException e) {
                    return;
                }
            }
        }

    }


}

Answer 1

Well, I will answer my question. My code is ok. I've discovered few minutes ago that the problem is the implementation of the PowerManager in the Eken M009S tablets, (a chinese tablet), the device where I've made the tests. In other devices, like in Samsung's cell phones, the PARTIAL_WAKE_LOCK works perfectly.