Desktop, Embedded and Mobile Apps with Vortex Café

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One Standard, One set of Tools, One Goal — Ubiquitous Data Sharing

The Vortex PlatformVORTEXWeb

VORTEXLite

VORTEXGateway

VORTEXCloud

PrivateClouds

VORTEXTools

• Insight • Record/Replay • Tuner • Tester • Configurator

OpenSpliceEnterprise

VORTEXCafé

Vortex Café

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Pure Java version of Vortex targeting JVM and embedded JVMs

DDSI Protocol Stack optimised for mobility and Android OS

Only DDS on the market designed and Engineered for Android

Vortex Café

J2SE

DDSI$$(Optimised*for*Mobility)*

DDS$API Java Scala JavaScript

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Vortex Café has a Staged Event Driven Architecture (SEDA) that allows it to be easily configured to trade off between throughput and latency

A Staged Event Driven Architecture

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Decomposes a complex, event-driven application into a set of stages connected by queues

Avoids the high overhead associated with thread-based concurrency models, and decouples event and thread scheduling from application logic.

Through admission control on each event queue, SEDAs can be well-conditioned to load, preventing resources from being overcommitted when demand exceeds service capacity

SEDA

[Matt Welsh, David Culler, and Eric Brewer, SEDA: An Architecture for Well-Conditioned, Scalable Internet Services]

http://en.wikipedia.org/wiki/Computer_program

http://en.wikipedia.org/wiki/Thread_(computer_science)

http://en.wikipedia.org/wiki/Concurrency_(computer_science)

http://en.wikipedia.org/wiki/Event_queue

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The Vortex Café architecture is organized around three stages

Packet Processing Message Processing Data Processing

The channel that connect each stage can be configured to be active or passive

Vortex Café Architecture

Packet Processor

Message Processor

Data Processor

Network Packet

DDSI Messages

Cache Changes

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Channels can be active or passive (and zero-copy). That means that channels can be configured with threading resources, or not

Messages posted in a passive channel are executed in the context of the posting thread

This allows to configure Vortex Café to optimize the use case at hand

Configurability

Processor

Channel

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Single Thread per Message

Sample Configurations

Packet Processor

Message Processor

Data Processor

Network Packet

DDSI Messages

Cache Changes

Fully Asynchronous

Packet Processor

Message Processor

Data Processor

Network Packet

DDSI Messages

Cache Changes

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Vortex Café is SEDA architecture as well as all the protocol parameters can be configured through configuration file or via command line properties , i.e. providing -D options to the JVM

Configuration parameters are listed on the user manual

Example:

Configuration in Practice

java -‐server -‐cp .:./target/vortex-‐cafe-‐demo-‐assembly-‐2.0.jar \ -‐Ddds.listeners.useTransportThread=true \ -‐Dddsi.writers.heartbeatPeriod=0.001 \ -‐Dddsi.writers.nackResponseDelay=0 \ -‐Dddsi.readers.heartbeatResponseDelay=0 \ -‐Dddsi.timer.threadPool.size=1 \ -‐Dddsi.receiver.threadPool.size=0 \ -‐Dddsi.dataProcessor.threadPool.size=0 \ -‐Dddsi.acknackProcessor.threadPool.size=0 \ -‐Dddsi.writers.reliabilityQueue.size=128 \ com.prismtech.cafe.demo.perf.RoundTripDemoReader $*

Anatomy of a Vortex-Cafe App

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• DomainParticipant: Provides access to a data cloud -- called a domain in DDS

• Topic: Domain-wide definition of a kind of Information

• Publisher/Subscriber: Provide scope to data sharing through the concept of partitions

• DataReader/DataWriter: Allow to read/write data for a given topic in the partitions their Subscriber/Publisher are associated with.

DDS Entities

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Brewing Vortex-Cafeint domain_id = 18; DomainParticipantFactory dpf = DomainParticipantFactory.getInstance(env) !DomainParticipant dp = dpf.createParticipant(domainId); Topic<Post> topic = dp.createTopic(“Post”, Post.class);

struct Post { string name; string msg; }; #pragma keylist Post name

Publisher pub = dp.createPublisher(); DataWriter<Post> dw = pub.createDataWriter<Post>(topic); dw.write(new Post(“Barman”, “Would you like an espresso?”);

Subscriber sub = dp.createSubscriber(); DataReader<Post> dr = sub.createDataReader<Post>(topic); LoanedSamples<Post> samples = dw.read();

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Escalating Vortex-Cafe

val topic = Topic[Post](“Post”) struct Post { string name; string msg; }; #pragma keylist Post name

val dw = DataWriter[Post](topic) dw write(new Post(“Barman”, “Would you like an espresso?”)

val dr = DataReader[Post](topic) dr.listen { case DataAvailable(_) => dr.read.foreach(println(_.getData()) }

Android

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4Android applications are written in the Java programming language

Support for native code is available, but this often leads to worse performance (due to the JNI layer) and worse battery utilisation

Thus unless you have very good reasons not to, you are strongly encouraged to write android applications in Java and to leverage on Java libraries!

Android Fundamentals

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An Android application runs in its own JVM and (by default) on its own linux process

An application may be composed of the following elements:

- Activities: a single screen with a user interface

- Services: a component that runs in the background to perform long-running operations or to perform work for remote processes.

- Content Providers: a component that manages shared data for a set of applications

- Broadcast Receivers: a component that responds to system-wide broadcast announcements

Android allows any applications to start any other application component and potentially consume the data it produces

Android Application in a Nutshell

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4Activities, Services and Broadcast Receivers are activated through an asynchronous message, called Intent

For Activities and Services the intent specifies the action to perform

For Broadcast Receivers it specifies the event being broadcasted, e.g. battery-low

Component Activation

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4The manifest is an XML file containing several important information about the application

Among, other things, the manifest includes the authorization necessary for your application -- for instance, it is in this file that you have to mention that your application requires access to the network, etc.

Application Manifest

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Notice that Activities are also destroyed each time there is a screen rotation (unless you don’t explicitly manage it)

Activities Life-Cycle

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Tasks and Back Tasks

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Considering the Android application lifecycle, we should ask ourselves a few questions:

When should we create DDS entities and who should hold a reference to them?

What happens when an application is no more visible?

Can I control when my application exits?

How do I deal with multi-threading?

DDS Considerations for Android

DDS Chat

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4To learn how to write an Android Application that uses Vortex Café we’ll develop a very simple Chat

To keep things simple this chat will have a single “chat room”

DDS Chat for Android

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Our Chat application will have a very simple architecture with simply one Activity that will take care of:

- Sending Posts into the ChatRoom

- Displaying Posts in the room since when we joined

In terms of information modelling, we’ll have a single topic representing the user post

Step 1: Architecture

struct Post { string name; string msg; }; #pragma keylist Post name

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Creating DDS entities, such as DomainParticipants, DataReaders and DataWriters involves network communication, such as discovery information

In addition when an a DDS entity is destroyed it looses its state

As such, tying the life-cycle of DDS entities to activities should be done with great care

Step 2: Lifecycle Management[1/2]

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In general, it is a better idea to tie the life-cycle of DDS entities to the Application as opposed to Activities

In some cases, it may make sense to tie the life-cycle of DataReaders/DataWriters to that of the activity that relies on them -- Usually this makes sense for activities that are “one-off”

Step 2: Lifecycle Management[2/2]

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Applicationpublic class ChatApplication extends Application {!! DataReader<Post> dr;! DataWriter <Post> dw;! DomainParticipant dp;!! @Override! public void onCreate() {! super.onCreate();! // This should be defined via a resource -- but for a small! // demo that’s OK.!

System.setProperty(ServiceEnvironment.IMPLEMENTATION_CLASS_NAME_PROPERTY,! "com.prismtech.cafe.core.ServiceEnvironmentImpl");! ServiceEnvironment env = ServiceEnvironment.createInstance(! ChatApplication.class.getClassLoader());! DomainParticipantFactory dpf =! DomainParticipantFactory.getInstance(env);!! dp = dpf.createParticipant(0);! Topic<Post> topic = dp.createTopic("Post",Post.class);! Publisher pub = dp.createPublisher();! Subscriber sub = dp.createSubscriber();!! dw = pub.createDataWriter(topic);! dr = sub.createDataReader(topic);! }!!

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Application

! public DataReader<Post> reader() {! return this.dr;! }!! public DataWriter<Post> writer() {! return this.dw;! }!!! @Override! public void onTerminate() {! super.onTerminate();! this.dp.close();! }!}!

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Manifest...

<application! android:allowBackup="true"! android:icon="@drawable/ic_launcher"! android:label="@string/app_name"! android:theme="@style/AppTheme" android:name="ChatApplication" >! <activity! android:name=“com.ddschat.MainActivity"! android:label="@string/app_name" >! <intent-filter>! <action android:name="android.intent.action.MAIN" />! <category android:name="android.intent.category.LAUNCHER" />! </intent-filter>! </activity>!</application>!

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When using Vortex Café you need to grant the proper permissions for networking:

More Manifest...

<uses-permission android:name="android.permission.INTERNET"/>!<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>!<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>!

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Activity GUI<?xml version="1.0" encoding="utf-8"?>!<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"! xmlns:tools="http://schemas.android.com/tools"! android:layout_width="match_parent"! android:layout_height="match_parent"! android:orientation="vertical" >!! <TextView android:id="@+id/chatMessages"! android:layout_width="match_parent"! android:layout_height="wrap_content"! android:text="@string/chat_msgs"! android:visibility="gone"! android:background="#666"! android:textColor="#fff"! android:paddingLeft="5dp"! />! <ListView! android:id="@+id/messageList"! android:layout_width="match_parent"! android:layout_height="0dp"! android:layout_weight="1"! />!!

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Activity GUI

! <LinearLayout! android:layout_width="fill_parent"! android:layout_height="wrap_content"! android:orientation="horizontal" >!! <EditText! android:id="@+id/message"! android:layout_width="0dp"! android:layout_height="wrap_content"! android:layout_weight="1"! android:hint="@string/edit_message" />!! <Button! android:layout_width="wrap_content"! android:layout_height="wrap_content"! android:onClick="sendChatMessage"! android:text="@string/button_send" />! </LinearLayout>!!!</LinearLayout>!

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Activity 1 ! 2 public class MainActivity extends Activity {! 3 ! 4 private static final String TAG = "ChatMainActivity";! 5 private final Handler handler = new Handler();! 6 private ArrayAdapter<String> chatMessages;! 7 ! 8 public class ChatMessageListener extends ChatMessageDataListener { ! 9 // ...!10 }!11 !12 @Override!13 protected void onCreate(Bundle savedInstanceState) {!14 super.onCreate(savedInstanceState);!15 setContentView(R.layout.activity_main);!16 chatMessages = new ArrayAdapter<String>(this, R.layout.messages);!17 chatMessages.add("Welcome to the DDS Chat Room");!18 ListView mview = (ListView) findViewById(R.id.messageList);!19 mview.setAdapter(chatMessages);!20 ChatApplication app = (ChatApplication) getApplication();!21 !22 app.reader().setListener(new ChatMessageListener());!23 !24 }!25

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Activity

!25 !26 @Override!27 public boolean onCreateOptionsMenu(Menu menu) {!28 // Inflate the menu; this adds items to the action bar if it is present.!29 getMenuInflater().inflate(R.menu.main, menu);!30 return true;!31 }!

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Activity

32 !33 public void sendChatMessage(View view) {!34 EditText editText = (EditText) findViewById(R.id.message);!35 String msg = editText.getText().toString();!36 editText.setText("");!37 // chatMessages.add(msg);!38 ChatApplication app = (ChatApplication) getApplication();!39 try {!40 Log.i(TAG, ">>> Sending data " + msg);!41 app.writer().write(new Post(usr, msg));!42 } catch (TimeoutException te) {!43 }!44 }!45 !46 }!

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Receiving data is a bit trickier since in Android only the thread that runs an activity has the right to change the UI

This means, that from a DDS listener it is not possible to change an the UI directly!

The solution is to use an Android Handler to which we can post Runnable to be executed by the activity thread

Let’s see how this works...

Receiving Data

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DDS Listener & Android Handler

1 public class ChatMessageListener extends ChatMessageDataListener {! 2 ! 3 private DataReader<Post> dr;! 4 ! 5 public ChatMessageListener() {! 6 ChatApplication app = (ChatApplication) getApplication();! 7 dr = app.reader();! 8 }! 9 !

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DDS Listener & Android Handler

10 @Override!11 public void onDataAvailable(DataAvailableEvent<Post> dae) {!12 final Iterator<Post> i = dr.read();!13 !14 Log.i(TAG, ">>> DataReaderListener.onDataAvailable");!15 if (i.hasNext()) {!16 Runnable dispatcher = new Runnable() {!17 public void run() {!18 while (i.hasNext()) {!19 Sample<Post> s = i.next();!20 !21 if (s.getSampleState() == SampleState.NOT_READ) {!22 Post cm = s.getData();!23 chatMessages.add(cm.name + " > " + cm.msg);!24 }!25 }!26 }!27 };!28 handler.post(dispatcher);!29 }!30 }!31 }!

Raspberry Pi

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The Raspberry Pi is a low cost, credit-card sized computer that plugs into a computer monitor or TV, and uses a standard keyboard and mouse

Raspberry Pi can interact with the outside world, and is used in a wide array of digital maker projects, from music machines and parent detectors to weather stations and tweeting birdhouses with infra-red cameras, etc.

Raspberry Pi