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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