webOS Open Source Edition Architecture
The following figure shows the overall architecture of webOS Open Source Edition (OSE). webOS OSE consist of a set of layers: Core Applications, Application Framework, Managers & Services, Base Components, and BSP/Kernel.
webOS OSE has Core applications as the top layer and this layer includes System UI and System app.
System UI includes apps that are related to the basic user interface, such as Home Launcher and Notification. These apps are usually implemented using QML.
System app includes Settings app and web browser. Settings app is used to control the system properties and implemented using Enact. As a web browser, the Chromium browser is used.
Enact is a web app framework optimized for developing web apps for webOS OSE. For more information and structure of Enact, refer to Enact developer site.
Enact is also an open source project and is provided separately from webOS OSE.
The SDK provides a development environment for web apps and services. In this release of webOS OSE, we provide a CLI-based SDK for developing and installing web apps and services. Web apps can be packaged with services that are developed using Node.js. For more details on development/packaging of web apps and services, see Command Line Interface.
Managers & Services
Managers & Services layer includes the following components.
System and Application Manager
System and Application Manager (SAM) oversees the behavior of apps. SAM manages each app throughout its lifecycle, including the installation, launch, termination, and removal of the app.
There are two types of apps in webOS Open Source Edition: native app and web app. In case of a web app, actual launching and management are performed by Web Application Manager as described below.
Web Application Manager
Web Application Manager (WAM) is responsible for launching and managing web apps. In addition, WAM performs CPU usage optimization, status monitoring and recovery processing, and access privileges management, all based on the running status of web apps.
Luna Surface Manager
Luna Surface Manager (LSM) is a component that works as a graphics manager. LSM displays graphical elements on the screen, manages the composition of these elements, and performs the event handling for input devices such as keyboard and pointer. LSM is also responsible for the execution and management of System UI, such as Home Launcher and Notification. LSM is implemented using Qt, and System UI is implemented using QML.
Activity Manager is responsible for managing and executing activities requested from services. An activity is requested along with a specific condition, and it is triggered when the condition is met. You can configure the activity to perform tasks such as automatic execution of specific services, callback requests, and so on.
uMediaServer (uMS) is a module that works as a server for the webOS media framework. uMS provides interfaces for media playback, manages resources, pipelines, and their policies, and manages the lifecycle of the media player.
Base Components layer includes the following components.
LS2, also called Luna Bus, is a system bus used by webOS OSE as the IPC mechanism used between components in webOS. It is composed of:
Client library - Provides API support to register on the bus and communicate with other components.
Central hub daemon - Provides a central clearing house for all communication. Utilities for monitoring and debugging the bus are included.
For more information about LS2, please see LS2 API Development.
Chromium also includes browser logics a.k.a. Chromium browser which webOS OSE provides as the default browser app.
DB8 is an embedded JSON database that supports data storing and retrieving in the structure of key-value store. webOS OSE uses LevelDB as the back-end database. The default service associated with DB8 is the com.webos.db. The com.webos.tempdb, which allows you to configure temporary storage in memory, is also provided.
BSP/Kernel layer consists of several components to support Raspberry Pi 3. Typically, it provides evdev for event processing, Mesa for graphics support, and Wi-Fi and wired LAN for connectivity.