Throwing and Cathcing Signals

Signals vs Messages

Messages are directed toward a specific recipient node, Signals however are broadcast to all potential listeners.

Both Messages and Signals can include correlation keys, called MessageKeys to specify specific scope

Therefore, Signals are best used for events that may affect multiple processes or multiple nodes.

Defining Signals Catch Events

In this example, we will demonstrate how can two seperate processes communicate through Signals

P.S. To define a Signal or a Message in the on-line modeler you need to click '+' to create the Signal first.

In this Process we have 3 User Tasks (Task 1,2,3). Each of the above Tasks have a Boundary Event of type Signal Catch Event. Boundary Events start with the parent Task, and wait to be invoked. These events are: - Intrrupting; meaning then invoked they will cancel the parent Task - Have a SignalId Cancel_All

Throw the Signal

The simplest way to invoke a Signal is through a Throw Signal Event In the above example, we add a User Task Cancel ?, when Invoked by User, It with Throw the Signal Cancel_All, this will cause all waiting User Tasks to be cancelled.

Another Way to Throw the Signal is using TypeScript Code as follows:

    let instances = await api.engine.throwSignal('Cancel_All',{},{"data.caseId":1001},user);

Here is the full code sample:

import { configuration } from './';
import { BPMNServer,BPMNAPI, Logger, SecureUser } from './';

const logger = new Logger({ toConsole: false});
const server = new BPMNServer(configuration, logger, { cron: false });
const api = new BPMNAPI(server);
let user = new SecureUser({userName:'user1',userGroups:['admin']});


testSignal();

async function testSignal() {

    let name = 'signal';
    console.log('starting ',name);
    //  delete existing cases
    await api.data.deleteInstances({caseId:1001},user);

    //  start the process
    let response = await api.engine.start(name, {caseId:1001},user);
    report(response.instance);

    console.log('--------------------');

    // throw the signal - once only     - should be caught by 3 items
    //  we restrict the signal to only one particualr caseId:1001

    let instances = await api.engine.throwSignal('Cancel_All',{},{"data.caseId":1001},user);

    console.log(`sigal was caught by ${instances.length} items`);

    for(let  i=0;i<instances.length;i++){
        let item=await api.data.findItem({"items.id":instances[i].itemId},user);
        console.log(`-Item  ${item.elementId} - ${item.status}  was invoked by the signal`);
    }

}
function report(instance) {
    var item1 = instance.items.forEach(item => {
        console.log(`- ${item.elementId} - ${item.status} `);
    })
}