Event Driven Design

21 Aug 2018

Introduction

Observer Pattern

Centralized Event Management

Decouple event from event handling

Implementation

Queue Single Thread, queue, watch

Operating System, Kernel mode, user mode

select / epoll model

GUI Design

Updating UI in dedicated thread. Single Thread UI / main thread

epoll

Windows

Android

AsyncTask

Vue

vm._events[event] stores an array of listener functions: (vm._events[event] || (vm._events[event] = [])).push(fn)

vm.$emit
vm.$on
vm.$once( event, callback )
vm.$off( [event, callback] )

// node_modules/vue/src/core/instance/events.js
export function eventsMixin (Vue: Class<Component>) {
  const hookRE = /^hook:/
  Vue.prototype.$on = function (event: string | Array<string>, fn: Function): Component {
    const vm: Component = this
    if (Array.isArray(event)) {
      for (let i = 0, l = event.length; i < l; i++) {
        this.$on(event[i], fn)
      }
    } else {
      (vm._events[event] || (vm._events[event] = [])).push(fn)
      // optimize hook:event cost by using a boolean flag marked at registration
      // instead of a hash lookup
      if (hookRE.test(event)) {
        vm._hasHookEvent = true
      }
    }
    return vm
  }

Javascript Event

https://developer.mozilla.org/en-US/docs/Web/API/Event

Java Event

In Java, we implement event using interface, See https://docs.oracle.com/javase/tutorial/uiswing/events/intro.html

Event Hierarchy

Centralized management

sub event

distributed management

pub/sub

Programming Models and Phylosophy

A Core Pattern for Events Adila A. Krisnadhi1;2 and Pascal Hitzler1 1 Wright State University, OH, USA 2 Universitas Indonesia, Depok, Indonesia

Refernces:

https://github.com/mspnp/architecture-center/blob/master/docs/patterns/event-sourcing.md

Asylum