PARTIAL_WAKE_LOCK and thread running in a service
<p>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.</p>

<p>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?</p>

<p>This is part of the code of the main activity, where the service is stareted:</p>

<pre><code>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));
    }
}
</code></pre>

<p>This is the code of the service:</p>

<pre><code>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;
                }
            }
        }

    }


}
</code></pre>
