Talk about hot to build a sustainable app with background service and an IPC mechanism

1. Build a sustainable app with an IPC
mechanism
IPC: AIDL is Sexy, not a
curse

2. Yonatan Levin

3. > 10M users
Ruby, Golang,
Python,
Android, iOS
52 cities

4. > 1000
members
Largest
StudyJam
in the World
Android
Academy

5. What are we going to do?

6. Learn how to talk
➔Became best fellows with IPC
➔Best friends with Binder
➔Fall in love with AIDL

7. Goal:
Make our app run smooth in the background while
performing multiple long tasks (like playing music)
unrelated to the UI

9. DarthVaderActivity
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.darth_vader_activity);
findViewById(R.id.iv_dva_build_death_star).setOnClickListener(this);
findViewById(R.id.iv_dva_interact_with_luke).setOnClickListener(this);
}

10. EmpireService
<service
android:name=".EmpireService"
android:enabled="true"
android:process=":remote">
</service>

11. Why separate process?
● GC not affecting your app
● Crashing not affecting UI
● Less chance to be killed:
○ Process serving others has at least the ranking of those it serve
○ Process with Service > Process with Background activities
● New Heap Space
● Smaller cold start + resource efficiency
● Because we can! :)

12. Why and when not?
●If you don’t have driver licenses
●Memory leaks
●Two process
●Keep it simple, stupid

13. https://github.com/parahall/AIDLServiceExample.git
Try this at home

14. IPC?
Inter-process communication (IPC)
is a framework for the exchange of
signals and data across multiple
processes

15. Linux legacy

16. Android

17. Why Binder?
Performance Security Stability Memory

18. Benefit for free
●Thread migration
●Identifying senders to receivers
●Unique object-mapping across process
●AIDL!!!!
●Bult-in support for marshalling
●Local execution mode (no IPC) if same process

19. We are already using binder today
●LifeCycle callbacks (onResume, OnDestroy) invoked by
ActivityManagerService
●Intents
●Content Provider

20. 1
IPC using Intent
git checkout IPCwithIntent

21. DarthVaderActivity
@Override
public void onClick(View v) {
Intent intent = new Intent(this, EmpireService.class);
switch (v.getId()) {
case R.id.iv_dva_build_death_star:
intent.putExtra(COMMAND_TYPE,
EmpireService.EmpireServiceCommands.BUILD_DEATH_STAR);
break;
case R.id.iv_dva_interact_with_luke:
intent.putExtra(COMMAND_TYPE,
EmpireService.EmpireServiceCommands.FIND_LUKE);
break;
}
mStartedCommandTime = System.currentTimeMillis();
startService(intent);
}

22. DarthVaderActivity
public class EmpireServiceReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Log.d(TAG,"Time took: " +String.valueOf(System.currentTimeMillis()-
mStartedCommandTime));
Toast.makeText(DarthVaderActivity.this, "Death Star deployed and ready for
your command, my lord",
Toast.LENGTH_LONG).show();
}
}

23. EmpireService
public int onStartCommand(Intent intent, int flags, int startId) {
EmpireServiceCommands command = (EmpireServiceCommands) intent.getExtras()
.get(COMMAND_TYPE);
switch (command) {
case BUILD_DEATH_STAR:
..do some hard work...
Intent jobDoneIntent = new Intent(EMPIRE_SERVICE_ACTION);
jobDoneIntent.putExtra("result",
new DeathStar(270000, 270000, "THIS IS THE BIG GUN"));
sendBroadcast(jobDoneIntent);
break;
case FIND_LUKE:
break;
}
stopSelf();
return START_NOT_STICKY;
}

24. Pain?
Not really OOP
Async only
Loosely-defined
Not so fast
High Level Abstraction of Binder

25. 2
IPC using Messenger
git checkout IPCwithMessenger

26. A reference to a Handler that can be sent to a remote process via
an Intent
Messages sent by the remote process via the messenger are
delivered to the local handler
Relatively fast
Overview

27. DarthVaderActivity
public void onClick(View v) {
Intent intent = new Intent(this, EmpireService.class);
Messenger messenger = new Messenger(new DarthVaderHandler(this));
intent.putExtra("ImperialMessenger", messenger);
switch (v.getId()) {
case R.id.iv_dva_build_death_star:
intent.putExtra("Command type",
EmpireService.EmpireServiceCommands.BUILD_DEATH_STAR);
break;
case R.id.iv_dva_interact_with_luke:
intent.putExtra("Command type",
EmpireService.EmpireServiceCommands.FIND_LUKE);
break;
}
startService(intent);
}

28. DarthVaderActivity
private static class DarthVaderHandler extends Handler {
private final WeakReference<DarthVaderActivity> clientRef;
public DarthVaderHandler(DarthVaderActivity client) {
this.clientRef = new WeakReference<>(client);
}
...//Handle message
}

29. DarthVaderActivity
private static class DarthVaderHandler extends Handler {
@Override
public void handleMessage(Message msg) {
Bundle data = msg.getData();
DarthVaderActivity client = clientRef.get();
if (client != null && msg.what == EmpireService.CALLBACK_MSG && data != null) {
Toast.makeText(client, "Death Star deployed and ready for your command, my lord",
Toast.LENGTH_LONG).show();
}
}
}

30. EmpireService
public int onStartCommand(Intent intent, int flags, int startId) {
Messenger messenger = intent.getParcelableExtra("ImperialMessenger");
EmpireServiceCommands command = (EmpireServiceCommands) intent.getExtras()
.get("Command type");
… more code coming...

31. EmpireService
switch (command) {
case BUILD_DEATH_STAR:
..do some hard work...
if (messenger != null) {
Message message = Message.obtain();
message.what = CALLBACK_MSG;
Bundle data = new Bundle(1);
data.putParcelable("result",
new DeathStar(270000, 270000, "THIS IS THE BIG GUN"));
message.setData(data);
try {
messenger.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
break;

32. But what if...
We want sync calls?
Full OOP
Business Transparent

33. 3
IPC using AIDL
git checkout IPCwithAIDL

34. Android Interface Definition Language (AIDL)
Our business operation on top of Binder object
Java-like interface
Defined in a separate .aidl file
AIDL Generate code of real java interface

35. .AIDL interface
interface IStarWars {
String buildDeathStar(out DeathStar deathStar);
oneway void findLuke(in IEmpireServiceResponseListener listener);
}

36. DeathStar.aidl
package com.academy.android.aidlserviceexample;
// Declare DeathStar so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable DeathStar;

37. IEmpireServiceResponseListener.aidl
interface IEmpireServiceResponseListener {
void onResponse(String response);
}

38. IStarWars.Stub
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder
implements com.academy.android.aidlserviceexample.IStarWars {
@Override
public java.lang.String buildDeathStar(
com.academy.android.aidlserviceexample.DeathStar deathStar)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.lang.String _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_buildDeathStar, _data, _reply, 0);
… not really necessary to dig in

39. Interface directional flag
in means that the object is transferred from client to service and
only used for inputs. If any changes are made to the bar object in
the service then they won’t reflect in the client.
out indicates that the object has no relevant data and will be
populated by the service and returned as a response.
inout means that the data gets copied, i.e., if any changes are
made to bar in the service then that’ll also reflect in the client’s
bar object.

40. AIDL Data Types
All primitives and arrays of
primitives
FileDescriptor
Serializable/Parcelable****
Map
Bundle
List
SparseArray

41. Sync Call - Death Star
Let the fun begin!

42. IStarWarsImplementation
public class IStarWarsImplementation extends IStarWars.Stub {
public String buildDeathStar(DeathStar deathStar) throws RemoteException {
...doing hard work..
deathStar.setBFG("BIG GUN IS VERY VERY");
deathStar.setHeight(270000);
deathStar.setWidth(270000);
return "Death Star deployed and ready for your command, my lord";
}
…
other interface methods

43. EmpireService
public class EmpireService extends Service {
private IStarWarsImplementation service;
@Override
public void onCreate() {
super.onCreate();
service = new IStarWarsImplementation();
}

44. EmpireService
@Override
public IBinder onBind(Intent intent) {
return service;
}
@Override
public boolean onUnbind(Intent intent) {
return super.onUnbind(intent);
}
@Override
public void onDestroy() {
this.service = null;
super.onDestroy();
}

45. DarthVaderActivity
public class DarthVaderActivity extends Activity implements ServiceConnection {
@Override
protected void onResume() {
super.onResume();
final boolean isServiceBounded = super.bindService(new Intent(this,
EmpireService.class),
this, BIND_AUTO_CREATE);
if (!isServiceBounded) {
Log.w(TAG, "Failed to bind to service");
}
}
… more methods

46. DarthVaderActivity
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
this.service = IStarWars.Stub.asInterface(service);
}
@Override
public void onServiceDisconnected(ComponentName name) {
this.service = null;
}

47. DarthVaderActivity
@Override
public void onClick(View v) {
try {
switch (v.getId()) {
case R.id.iv_dva_build_death_star:
DeathStar deathStar = new DeathStar();
final String reply = service.buildDeathStar(deathStar);
String buildDeathStar = String
.format("%s and it have %s", reply, deathStar.getBFG());
Toast.makeText(this, buildDeathStar, Toast.LENGTH_LONG).show();
break;
}
} catch (RemoteException e) {
e.printStackTrace();
}

48. ASync Call - Find a luke

49. .AIDL interface
interface IStarWars {
String buildDeathStar(out DeathStar deathStar);
oneway void findLuke(in IEmpireServiceResponseListener listener);
}
interface IEmpireServiceResponseListener {
void onResponse(String response);
}

50. IStarWarsImplementation
...other AIDL interface implementation methods
@Override
public void findLuke(IEmpireServiceResponseListener listener) throws RemoteException
{
..Doing very hard job through couple episodes…
listener.onResponse("I'm your father, Luke!");
}

51. DarthVaderActivity
IEmpireServiceResponseListener.Stub mListener
= new IEmpireServiceResponseListener.Stub() {
@Override
public void onResponse(final String response) throws RemoteException {
//Other process. We should run on UI Thread in order to interact with UI
mHandler.post(new Runnable() {
@Override
public void run() {
Toast.makeText(DarthVaderActivity.this, response,
Toast.LENGTH_LONG)
.show();
}
});
}
};

52. DarthVaderActivity
@Override
public void onClick(View v) {
try {
switch (v.getId()) {
case R.id.iv_dva_interact_with_luke:
service.findLuke(mListener);
break;
}
} catch (RemoteException e) {
e.printStackTrace();
}
}

53. Binder Overhead:
0 ms

54. What did we get?
Services running on separate process
Easy expandable communication
Great performance
Fun :)

55. levinyon@gmail.com
facebook.com/levin.yonatan