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diff --git a/docs/3_Developer_Guides/1_Application_Framework/1_Introduction.md b/docs/3_Developer_Guides/1_Application_Framework/1_Introduction.md deleted file mode 100644 index 957858a..0000000 --- a/docs/3_Developer_Guides/1_Application_Framework/1_Introduction.md +++ /dev/null @@ -1,150 +0,0 @@ ---- -title: Introduction ---- - -# Foreword - -The AGL Application Framework is nothing new. However, the implementation used up until -the `lamprey` release has been retired starting with the `marlin` release and replaced -by a redesigned Application Framework one. However, this new implementation isn't a 1:1 -replacement, and as such it doesn't provide all of the features of the previous -Application Framework. Some of those will be added back over time, others have been -discarded in favor of more modern and/or widely-used alternatives. - -# Introduction - -As a provider of an integrated solution to build up on, AGL needs to define a reliable -and well-specified method for managing the deployment and integration of applications -and services, as well as the way they can interact with the rest of the system. - -This is achieved by providing a common set of rules and components, known as the -Application Framework. By ensuring conformity to those rules, application developers -can have a good understanding of the requirements for creating and packaging -applications targeting AGL-based systems. Likewise, system developers and integrators -have a clear path for including such applications in AGL-based products. - -The Application Framework's scope extends to the following areas: -- system services integration and lifecycle management -- user session management, including user-level applications and services lifecycle - management -- inter-process communication - -In order to be as simple as possible and avoid any unneded custom implementation, the -Application Framework relies mainly on third-party technologies and/or software -components, most of those being maintained under the -[freedesktop.org](https://www.freedesktop.org) umbrella. Those include: - - -- [systemd](https://www.freedesktop.org/wiki/Software/systemd/): system services and user session services management - - -- [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/): inter-process communication - - -- [Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/): - application enumeration and startup - -AGL also provides reference implementations whenever possible and relevant, located in -the [meta-agl](/3_Developer_Guides/6_AGL_Layers/2_meta-agl/) layer under `meta-app-framework`. At the -moment, the Application Framework contains 2 such components: - -- `agl-session`: `systemd` unit files for user sessions management - -- `applaunchd`: application launcher service - -# Services management - -Both system and user services are managed by `systemd`, which provides a number of -important features, such as dependency management or service monitoring: when starting -a service, `systemd` will ensure any other units this service depends on are available, -and otherwise start those dependencies. Similarly, `systemd` can automatically restart -a crashed service, ensuring minimal downtime. - -`systemd` also provides an efficient first layer of security through its -[sandboxing](https://www.freedesktop.org/software/systemd/man/systemd.exec.html#Sandboxing) -and other security-related options. - -It is also well integrated with D-Bus and can be used for a more fine-grained control -over D-Bus activated services: by delegating the actual service startup to `systemd`, -developers can take advantage of some of its advanced features, allowing for improved -reliability and security. - -Each service should be represented by a `systemd` unit file installed to the appropriate -location. More details can be obtained from the [Creating a New Service](/3_Developer_Guides/2_Creating_a_New_Service/) -document. - -# User session management - -Similarly, user sessions and the services they rely on are also managed by `systemd`. - -AGL provides 2 `systemd` units: - - -1\. `agl-session@.service` is a template system service for managing user sessions; it -takes a username or UID as a parameter, creating a session for the desired user. -Instanciating this service can be achieved by enabling `agl-session@USER.service`, for -example by executing the following command on a running system: - -``` -$ systemctl enable agl-session@USER.service -``` - -By default, AGL enables this service as `agl-session@agl-driver.service`, running as -user `agl-driver`. - -*Note: while you can create sessions for as many users as needed, only one instance of -`agl-session@.service` is allowed per user.* - - -2\. `agl-session.target` is a user target for managing user services and their -dependencies. It is started by `agl-session@.service`. - -By default, `agl-compositor` is part of this target. It is therefore automatically -started for user `agl-driver`. - -Any other service needed as part of the user session should similarly depend on this -target by appending the following lines to their unit file: - -``` -[Install] -WantedBy=agl-session.target -``` - -# Inter-process communication - -In order to provide a "standard", language-independent IPC mechanism and avoid the need -for maintaining custom bindings for each programming language to be used on top of AGL, -the Application Framework promotes the use of [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/) -as the preferred way for applications to interact with services. - -Most services already included in AGL provide one or several D-Bus interfaces, and can -therefore interact with D-Bus capable applications and services without requiring any -additional component. Those services include, among others: - -- [ConnMan](https://git.kernel.org/pub/scm/network/connman/connman.git/): network connectivity - -- [BlueZ](http://www.bluez.org/): Bluetooth connectivity - -- [oFono](https://git.kernel.org/pub/scm/network/ofono/ofono.git): telephony and modem - management - -- [GeoClue](https://gitlab.freedesktop.org/geoclue/geoclue/-/wikis/home): geolocation - -# Application launcher service - -As mentioned above, the Application Framework follows the guidelines of the -[Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/) -for application enumeration and startup. - -As no simple reference implementation exists for this part of the specification, AGL -provides an application launcher service named `applaunchd`. This service is part of the -default user session, and as such is automatically started on session startup. It can -therefore be considered always available. - -`applaunchd` enumerates applications installed on the system and provides a D-bus -interface for services and applications to: -- query the list of available applications -- request the startup and/or activation of a specific application -- be notified when applications are started or terminated - -`applaunchd` is described with more details in [the following document](../2_Application_Startup/). |