Python Script for Location Updates

Below is a simple python script to automate location updates to the emulator.

	# Karun Matharu (ksm113@imperial.ac.uk)
	# Imperial College London
	# A simple python telnet script to connect to the emulator on
	# localhost 5554 and issue geo fix commands
	import sys
	import telnetlib
	import getpass
	import time
	import random
	HOST = "localhost"
	PORT = 5554
	TIMEOUT = 2
	# Sleep time between each location update
	TIME_GAP = 4
	# Starting values for longitude and latitude
	lon = 50.000000
	lat = 50.000000
	tn = telnetlib.Telnet(HOST, PORT, TIMEOUT)
	print tn.read_some()
	while (True):
	a = random.random()
	b = random.random()
	lat = lat + a
	lon = lon + b
	s = "geo fix " + str(lon) + " " + str(lat) + "\n"
	tn.write(s)
	print(s)
	time.sleep(TIME_GAP)

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Location Updates within a Service

Requesting location updates within a remote service may cause the following exception:

runException Can't create handler inside thread that has not called Looper.prepare()

The requestLocationUpdates() function requires access to a Looper to deal with messages in a queue. When calling this method in a background service, the method may not implicitly have access to the threads Looper. Defining the thread's Looper explicitly by adding an additional argument 'Looper.getMainLooper()' deals with the issue.

	locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 4000, 0, listener, Looper.getMainLooper());

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Dealing with System Service Dependencies

As an example of a case where a system service depends on another, below is the constructor for a 'test' service which when constructed, initializes a location manager.

	/*
	Import libraries and variable declarations
	*/
	public TestService(Context context) {
	super();
	mContext = context;
	mWorker = new TestWorkerThread("TestServiceWorker");
	mWorker.start();
	Log.i(TAG, "Spawned worker thread");
	//Initialize the locationManager when the TestService starts
	locationManager = (LocationManager) mContext.getSystemService(Context.LOCATION_SERVICE);
	}
	/*
	Other functions
	*/

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The 'test' service requires that the 'LocationManagerService' is running before 'test' is created so that it can successfully initialize  a location manager.

When Android is started, 'init' is a component of the bootloader sequence which initializes a number of daemons which run continuously whilst the operating system is running.

One of those daemons 'Zygote' is the process responsible for starting system services. It does this by executing the initAndLoop() function of the SystemServer Class.

SystemServer located in frameworks/base/services/java/com/android/server/SystemServer.java

In order to ensure 'LocationManagerService' is running before 'test' service, place the 'test' service's addService code anywhere below that of the 'LocationManagerService'.

	//Within initAndLoop()
	if (!disableLocation) {
	try {
	Slog.i(TAG, "Location Manager");
	location = new LocationManagerService(context);
	ServiceManager.addService(Context.LOCATION_SERVICE, location);
	} catch (Throwable e) {
	reportWtf("starting Location Manager", e);
	}
	try {
	Slog.i(TAG, "Country Detector");
	countryDetector = new CountryDetectorService(context);
	ServiceManager.addService(Context.COUNTRY_DETECTOR, countryDetector);
	} catch (Throwable e) {
	reportWtf("starting Country Detector", e);
	}
	}
	/*
	Register Other Services
	*/
	//Register Test Service
	try {
	Slog.i(TAG, "Test Service");
	ServiceManager.addService("test", new TestService(context));
	} catch (Throwable e) {
	Slog.e(TAG, "Failure starting TestService Service", e);
	}

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