276 lines
11 KiB
Markdown
276 lines
11 KiB
Markdown
# Pub Sub System - Publish and Subscribe System
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The Pub-Sub-System is a basic Publish and Subscribe System. A Pub-Sub System consists of 3 Main Elements:
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- Publishers
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- Subscribers
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- Broker
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Whereas Publishers publishes data on a given Topic, Subscribers receives updates of the data of a subscribed Topic. Topics are used as a Base to share data. For instance, if a Sensor publishes its value on the Topic `Room1.Temperature` every subscribtion which subscribes to `Room1` or `Room1.Temperature` will receive the updated Value. By unsubscribing, a Subscriber doesn't receive Updates anymore. Thereby, the Publish-and-Subscribe mechanism ensure, a loose coupleing between the Elements and scalability.
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Summarized Attributes of a Pub-Sub-System
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- A Publisher doesn't know its subscribers
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- A Subscriber doesn't kown the Publisher(s)
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- Different Publishers are able to Publish data on the same Topic
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- Broker are responsible for sharing data and subscriptions etc.
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---
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## Description of the Implementation
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The Basic Pub-Sub-System which is based on a Binary Tree-Model. For Instance, there are Publishers for the following Topics:
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- `Root.Topic1`
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- `Root.Topic2`
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- `Root.Topic2.Part1`
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- `Root.Topic2.Part2`
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- `Root.Topic2.Part3`
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Thereby the **Tree** is build up like that.
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```
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(Root)
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/ \
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/ \
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(Topic1) (Topic2)
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/ | \
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/ | \
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(Part1) | (Part2)
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(Part3)
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```
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Data of Topics are shared only to its '_Super-Topics_' and '_Child-Topics_' (see the Examples)
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### Example 1 - Publishing data on `Root/Topic2`
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If a Publisher of the Topic `Root.Topic2` publishes an update, the Subscribe of the following Topics receives an update.
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- `Root`
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- `Root.Topic2`
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- `Root.Topic2.Part1`
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- `Root.Topic2.Part2`
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- `Root.Topic2.Part3`
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Thereby each element gets the new Data in the following format:
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> **Example-Data:** `{ Part1 : 1, Part2 : 'test', Part3 : 1.337 }` is published on the Topic `Root/Topic2`
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| Topic | Received Data of the Subscription in **_JSON-Notation_** |
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| --------------------- | ---------------------------------------------------------------------------------------- |
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| `Root` | `{ Topic1: 'someData', Topic2 : { Part1 : 1, Part2 : 'test', Part3 : [1.337, 1.338] } }` |
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| `Root.Topic2` | `{ Part1 : 1, Part2 : 'test', Part3 : 1.337 }` |
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| `Root.Topic2.Part1` | `1` |
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| `Root.Topic2.Part2` | `'test'` |
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| `Root.Topic2.Part3` | `[1.337, 1.338]` |
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| `Root.Topic2.Part3.0` | `1.337` |
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| `Root.Topic2.Part3.1` | `1.338` |
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> Subscriber of the Topic `Root.Topic1` doesn't receive Updates.
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### Example 2 - Publishing data on `Root.Topic2.Part3`
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If a Publisher of the Topic `Root.Topic2.Part3` publishes an update, the Subscribe of the following Topics receives an update.
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- `Root`
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- `Root.Topic2`
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- `Root.Topic2.Part3`
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Thereby each element gets the new Data in the following format:
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> **Example-Data:** `[1234, 1.338]` is published on the Topic `Root.Topic2.Part3`
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| Topic | Received Data of the Subscription in **_JSON-Notation_** |
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| --------------------- | --------------------------------------------------------------------------------------- |
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| `Root` | `{ Topic1: 'someData', Topic2 : { Part1 : 1, Part2 : 'test', Part3 : [1234, 1.338] } }` |
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| `Root.Topic2` | `{ Part1 : 1, Part2 : 'test', Part3 : [1234, 1.338] }` |
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| `Root.Topic2.Part3` | `[1234, 1.338]` |
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| `Root.Topic2.Part3.0` | `1234` |
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| `Root.Topic2.Part3.1` | `1.338` No Update will be Pusblished, cause the value didn't change |
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> Subscriber of the Topic `Root.Topic1`, `Root.Topic2.Part1`, `Root.Topic2.Part3.1` and `Root.Topic2.Part2` doesn't receive Updates, cause their values didn't change.
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---
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## Technical Implementation
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The Pub-Sub-System is build up with a Base-Node-Container. This Container is responsible to create (if necessary) new Topics on which a Subscription could be subscribe or data could be published. Based on all available Subscriptions published Data send to the corresponding Subscriptions.
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- No multiple Pub-Sub-Systems at a Time, otherwise an exception is thrown.
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- **Subscribers must unsubscribe** if the should not listening any more. For Instance pause/deactivate or dispose an specific Object. (use the `unregister` function of a Subscribtion)
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- Subscriptions could be activated again by calling `register`
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- Subscriptions are automatically active.
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---
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## Observables
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Observables allow a simple integration of attributes of an object. Therefore the `IObserveable<T>` interface is used.
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### Example - Integrate an Observable
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To use an Observable the following code must be used, where as `TYPE` describes the data type like `number`, `string`, etc.
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```typescript
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@inject(PUBSUB.TYPES.Observable)
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public attributeName: PUBSUB.Observable<TYPE>;
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```
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Furthermore the Class containing the observable attribute **must** implement the **`IContainsObservables`-Interface**, as presented in the example below:
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```typescript
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/** Import the Pub-Sub-System (Path must be adapted) */
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import * as PUBSUB from "Pub-Sub-System/assembly/manual-assembly";
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/** Define a Class containing an observable @see attribute_01 */
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@injectable()
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class TestClass implements IContainsObservables {
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/** Values of the IOnlineValues - Interface */
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path: string = "";
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offeredTopics: Map<string, GenericObservable<any>>;
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/**
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* Defining the Attribute which should be integrated into the Publish
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* and Subscribe System. The value should be a 'number'
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*
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* @type {PUBSUB.Observer<number>}
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* @memberof TestClass
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*/
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@inject(PUBSUB.TYPES.Observable)
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public attribute_01: PUBSUB.Observable<number>;
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/**
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* Creates an instance of TestClass.
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* @memberof TestClass
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*/
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constructor() {
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/** Set a Values - That must be done during the construction */
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this.path = "";
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this.offeredTopics = new Map<string, GenericObservable<any>>();
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}
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}
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```
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### Working with Observables
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By default observables publish their content on an automatically generated Topic. This topic could be adapted and read with the `path` - attibute of an Observable.
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```typescript
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```
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#### Subscribing to Changes
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To subscribe to changes of an obserable simply use the metho `subscribe`. You can determine whether the subscription should receive the information `async` (Putting task on the next Tick of the Nodejs / JavaScript Eventloop) or `sync` (immediately).
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The Following Parameters are used:
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| Param | Type | Default | Description |
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| ------ | ---------------------------------------------------------- | -------- | -------------------------------------------------- |
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| func | [<code>subscriptionCallback</code>](#subscriptionCallback) | | Function which is called when new Datas are pushed |
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| [mode] | `'sync'` \ `'immediate'` | `'sync'` | Mode of the Subscription |
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**Returns**: <code>ISubscription</code> - The corresponding Subscription
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whereas the <code>subscriptionCallback</code> is defined as:
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| Param | Type | Description |
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| ----------- | ------------------- | --------------------------------------------- |
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| content | <code>any</code> | The new Data |
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| [topic] | <code>string</code> | The Topic on which the Data where from |
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| [timeStamp] | <code>number</code> | The timeStamp on which the data where changed |
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**Returns** - <code>void</code>
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##### Example
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```typescript
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/** Simplified Construction of the Object */
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const _test = new TestClass();
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/** Subscribe to changes of the attribute */
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_test.attribute_01.subscribe((_num, _topic) => {
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console.log("subscription on", _topic, ". Value changed to:", _num);
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}, "sync");
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/** Change the Value of the observable => Subscription will be triggered */
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_test.attribute_01.value = 1337;
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```
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#### Changing Values and reading values
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The value of an observable could be changed with the `value` attribute of an observable
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```typescript
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/** Simplified Construction of the Object */
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const _test = new TestClass();
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/** Change the Value of the observable => Subscription will be triggered */
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_test.attribute_01.value = 1337;
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/** Reading a Value */
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const _aVar = _test.attribute_01.value;
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```
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### Sample Application
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```typescript
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import { Builder } from "../../mod-Assembly-Builder/src/Container-Builder.FileLoader";
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import { DESCRIPTION, PubSubSystem } from "../assembly/manual-assembly";
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Builder.instance.addElements(DESCRIPTION.PROVIDED_CLASSES);
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Builder.instance.addActivationHandler(DESCRIPTION.ACTIVATIONHANDLERS);
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Builder.load();
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Builder.on("loaded", () => {
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// Create a Publish and Subscribe System
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const _pubSub = Builder.instance.container.get<PubSubSystem>(
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DESCRIPTION.TYPES.PubSubSystem
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);
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// Create a Subscription on the topic: "test.topic"
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const _sub = _pubSub.createSubscription<any>(
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"test.topic",
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(_data, _topic, _timestamp) => {
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console.log("received with inform", _data);
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}
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);
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// Create a Publisher and Publish "1" on a Subtopic
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_pubSub.createPublisher<number>("test.topic.child").publishData(1);
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_pubSub.createPublisher<number>("test.topic").publishData(2);
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// Change the Subscription Mode.
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_sub.options.mode = ["direct"];
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// The following Subscription will be now ignored
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_pubSub.createPublisher<number>("test.topic.child").publishData(3);
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_pubSub.createPublisher<number>("test.topic").publishData(4);
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});
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```
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Results in the Output
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```
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Changing Value to 1337
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Calling Subscription of root._id8ebg4qDkQjjx the 0'th time. Value changed to: 1337
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Adding Setter
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Changing Value to 133123
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In Setter of the attribute_01
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Calling Subscription of root._id8ebg4qDkQjjx the 1'th time. Value changed to: 100
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Reading after setter 100
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Changing Path
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Changing Value to 1337
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In Setter of the attribute_01
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In Setter of the attribute_01
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Calling Subscription of root._test.attribute_01 the 2'th time. Value changed to: 100
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create Link with Pub-Sub-System
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plublish 1336 on _test.attribute_01
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In Setter of the attribute_01
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Calling Subscription of root._test.attribute_01 the 3'th time. Value changed to: 1336
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plublish 1336 on _test.attribute_01
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Calling Subscription of root._test.attribute_01 the 4'th time. Value changed to: 1336
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```
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