Digging Into Android System Services

Walkthrough of the architecture that the Android platform uses to expose services to applications.

1. Digging Into Android System Services Dave Smith, PE @devunwired
2. Why Are You Here? Trace AOSP Code Learn Platform Internals Discover App Impact
3. Linux Kernel Hardware Abstraction Layer Native Services Runtime Application Framework Applications
4. Linux Kernel Hardware Abstraction Layer Native Services Runtime Application Framework Applications
5. Application System Server Manager Service
6. Application System Server Manager Service Application Manager Application Manager Application Manager
7. Context.getSystemService(SERVICE_NAME)
8. ContextImpl SystemServiceRegistry Context AlarmManager NotificationManager LocationManager PowerManager Context.getSystemService(SERVICE_NAME)
9. package android.app;
 
 final class SystemServiceRegistry {
 ...
 
 static {
 ...
 registerService(Context.ACCOUNT_SERVICE, AccountManager.class,
 new CachedServiceFetcher<AccountManager>() {
 @Override
 public AccountManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ACCOUNT_SERVICE);
 IAccountManager service = IAccountManager.Stub.asInterface(b);
 return new AccountManager(ctx, service);
 }
 });
 ...
 registerService(Context.ALARM_SERVICE, AlarmManager.class,
 new CachedServiceFetcher<AlarmManager>() {
 @Override
 public AlarmManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ALARM_SERVICE);
 IAlarmManager service = IAlarmManager.Stub.asInterface(b);
 return new AlarmManager(service, ctx);
 }
 });
 ...
 }
 } SystemServiceRegistry.java
10. package android.app;
 
 final class SystemServiceRegistry {
 ...
 
 static {
 ...
 registerService(Context.ACCOUNT_SERVICE, AccountManager.class,
 new CachedServiceFetcher<AccountManager>() {
 @Override
 public AccountManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ACCOUNT_SERVICE);
 IAccountManager service = IAccountManager.Stub.asInterface(b);
 return new AccountManager(ctx, service);
 }
 });
 ...
 registerService(Context.ALARM_SERVICE, AlarmManager.class,
 new CachedServiceFetcher<AlarmManager>() {
 @Override
 public AlarmManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ALARM_SERVICE);
 IAlarmManager service = IAlarmManager.Stub.asInterface(b);
 return new AlarmManager(service, ctx);
 }
 });
 ...
 }
 } SystemServiceRegistry.java
11. Application System Server Manager Service
12. Binder IPC Application System Server Service Manager
13. Application System Server Manager Service Binder IPC AIDL Proxy Stub
14. Application System Server AlarmManager AlarmManagerService IAlarmManager IAlarmManager.Stub Binder IPC
15. IAlarmManager.aidl AlarmManager.java package android.app;
 
 ...
 
 public class AlarmManager {
 private final IAlarmManager mService;
 ...
 
 public void setTime(long millis) {
 try {
 mService.setTime(millis);
 } catch (RemoteException ex) {
 throw ex.rethrowFromSystemServer();
 }
 }
 
 public void setTimeZone(String timeZone) {
 ...
 
 try {
 mService.setTimeZone(timeZone);
 } catch (RemoteException ex) {
 throw ex.rethrowFromSystemServer();
 }
 }
 } package android.app;
 
 interface IAlarmManager {
 void set(...);
 boolean setTime(long millis);
 void setTimeZone(String zone);
 void remove(...);
 long getNextWakeFromIdleTime();
 ...
 }
16. IAlarmManager.aidl AlarmManager.java package android.app;
 
 ...
 
 public class AlarmManager {
 private final IAlarmManager mService;
 ...
 
 public void setTime(long millis) {
 try {
 mService.setTime(millis);
 } catch (RemoteException ex) {
 throw ex.rethrowFromSystemServer();
 }
 }
 
 public void setTimeZone(String timeZone) {
 ...
 
 try {
 mService.setTimeZone(timeZone);
 } catch (RemoteException ex) {
 throw ex.rethrowFromSystemServer();
 }
 }
 } package android.app;
 
 interface IAlarmManager {
 void set(...);
 boolean setTime(long millis);
 void setTimeZone(String zone);
 void remove(...);
 long getNextWakeFromIdleTime();
 ...
 }
17. package com.android.server;
 
 public class AlarmManagerService extends SystemService {
 ... 
 private final IBinder mService = new IAlarmManager.Stub() { 
 @Override
 public boolean setTime(long millis) {
 getContext().enforceCallingOrSelfPermission(
 "android.permission.SET_TIME",
 "setTime");
 ...
 } 
 @Override
 public void setTimeZone(String tz) {
 getContext().enforceCallingOrSelfPermission(
 "android.permission.SET_TIME_ZONE",
 "setTimeZone");
 ...
 }
 }; 
 } AlarmManagerService.java IAlarmManager.aidl package android.app;
 
 interface IAlarmManager {
 void set(...);
 boolean setTime(long millis);
 void setTimeZone(String zone);
 void remove(...);
 long getNextWakeFromIdleTime();
 ...
 }
18. Binder IPC Application Service Object
19. Binder IPC Application Service Object Object
20. public class MainActivity extends Activity implements LocationListener {
 
 @Override
 protected void onResume() {
 super.onResume();
 
 LocationManager manager = (LocationManager) getSystemService(LOCATION_SERVICE);
 manager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
 }
 
 @Override
 protected void onPause() {
 super.onPause();
 
 LocationManager manager = (LocationManager) getSystemService(LOCATION_SERVICE);
 manager.removeUpdates(this);
 }
 
 @Override
 public void onLocationChanged(Location location) {
 ...
 }
 
 ...
 }
21. public class MainActivity extends Activity implements LocationListener {
 
 @Override
 protected void onResume() {
 super.onResume();
 
 LocationManager manager = (LocationManager) getSystemService(LOCATION_SERVICE);
 manager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
 }
 
 @Override
 protected void onPause() {
 super.onPause();
 
 LocationManager manager = (LocationManager) getSystemService(LOCATION_SERVICE);
 manager.removeUpdates(this);
 }
 
 @Override
 public void onLocationChanged(Location location) {
 ...
 }
 
 ...
 }
22. Application System Server Manager Service
23. Application System Server Manager Service Service Manager Stub Stub
24. Application System Server Manager Service Service Manager IBinder Stub IBinder
25. Application System Server Manager Service Service Manager Proxy Stub IBinder
26. $ adb shell service list Found 116 services: 0 carrier_config: [com.android.internal.telephony.ICarrierConfigLoader] 1 phone: [com.android.internal.telephony.ITelephony] 2 isms: [com.android.internal.telephony.ISms] 3 iphonesubinfo: [com.android.internal.telephony.IPhoneSubInfo] 4 simphonebook: [com.android.internal.telephony.IIccPhoneBook] 5 isub: [com.android.internal.telephony.ISub] 6 telecom: [com.android.internal.telecom.ITelecomService] 7 contexthub_service: [android.hardware.location.IContextHubService] 8 dns_listener: [android.net.metrics.IDnsEventListener] 9 connectivity_metrics_logger: [android.net.IConnectivityMetricsLogger] 10 imms: [com.android.internal.telephony.IMms] 11 media_projection: [android.media.projection.IMediaProjectionManager] 12 launcherapps: [android.content.pm.ILauncherApps] 13 shortcut: [android.content.pm.IShortcutService] 14 fingerprint: [android.hardware.fingerprint.IFingerprintService] 15 trust: [android.app.trust.ITrustManager] 16 media_router: [android.media.IMediaRouterService] 17 media_session: [android.media.session.ISessionManager] 18 restrictions: [android.content.IRestrictionsManager] 19 print: [android.print.IPrintManager] 20 graphicsstats: [android.view.IGraphicsStats] ...
27. package android.app;
 
 final class SystemServiceRegistry {
 ...
 
 static {
 ...
 registerService(Context.ACCOUNT_SERVICE, AccountManager.class,
 new CachedServiceFetcher<AccountManager>() {
 @Override
 public AccountManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ACCOUNT_SERVICE);
 IAccountManager service = IAccountManager.Stub.asInterface(b);
 return new AccountManager(ctx, service);
 }
 });
 ...
 registerService(Context.ALARM_SERVICE, AlarmManager.class,
 new CachedServiceFetcher<AlarmManager>() {
 @Override
 public AlarmManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ALARM_SERVICE);
 IAlarmManager service = IAlarmManager.Stub.asInterface(b);
 return new AlarmManager(service, ctx);
 }
 });
 ...
 }
 } SystemServiceRegistry.java
28. package android.app;
 
 final class SystemServiceRegistry {
 ...
 
 static {
 ...
 registerService(Context.ACCOUNT_SERVICE, AccountManager.class,
 new CachedServiceFetcher<AccountManager>() {
 @Override
 public AccountManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ACCOUNT_SERVICE);
 IAccountManager service = IAccountManager.Stub.asInterface(b);
 return new AccountManager(ctx, service);
 }
 });
 ...
 registerService(Context.ALARM_SERVICE, AlarmManager.class,
 new CachedServiceFetcher<AlarmManager>() {
 @Override
 public AlarmManager createService(ContextImpl ctx) {
 IBinder b = ServiceManager.getService(Context.ALARM_SERVICE);
 IAlarmManager service = IAlarmManager.Stub.asInterface(b);
 return new AlarmManager(service, ctx);
 }
 });
 ...
 }
 } SystemServiceRegistry.java
29. package com.android.server;
 
 import android.content.Context;
 
 public final class SystemServer {
 ...
 ConnectivityServicer connectivity = new ConnectivityService(
 context, networkManagement, networkStats, networkPolicy);
 ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity); 
 ...
 LocationManagerService location = new LocationManagerService(context);
 ServiceManager.addService(Context.LOCATION_SERVICE, location);
 ...
 } SystemServer.java
30. @devunwired +DaveSmithDev milehighandroid.com wiresareobsolete.com