Development/Tutorials/D-Bus/Autostart Services (es)

Development/Tutorials/D-Bus/Autostart Services

Creating and Installing D-Bus Autostart Services

Tutorial Series	D-Bus
Previous	Introduction Creating Interfaces
What's Next	n/a
Further Reading	n/a

Abstract

The D-Bus systems provides a mechanism to autostart applications if they aren't already running when a D-Bus call is made to a service provided by that program. This tutorial demonstrates how to create a D-Bus autostart service and integrate it into your CMake build.

The Basic Mechanics

Whenever a D-Bus message arrives for the D-Bus server to deliver, it looks for the corresponding service that the message is addressed to on the bus it was sent on.

If no such service is currently registered, it then falls back to looking through files kept in the services directory in the D-Bus data path, e.g. /usr/share/dbus-1/services. It looks through each *.service file one by one for a matching service name. It then uses this file to determine what application to launch, waits for the application to finish launching and then (if all goes well) delivers the message.

All of this happens transparently to the application the message originated with.

Creating a Service File

The service files are simple ".ini style" configuration files, much like standard .desktop files.

A valid service file:

ends with the suffix .service
has a [D-BUS Service] group
has a Name and Exec key

The contents of an example service file for an application called MyApp might look like this:

[D-BUS Service] Name=org.kde.myapp Exec=/usr/bin/myapp

The Name and Exec keys will be familiar to anyone who has worked with .desktop files before. Unlike .desktop files, though, the Exec line must contain the full path to the application that is to be started.

In the above example, if a message was sent to the org.kde.myapp service but such a service had not yet been registered on the bus, then /usr/bin/myapp will be launched. It is then up to myapp to register the proper service on the bus.

Instalando un fichero de servicio

Once you have created a service file for your application, place it somewhere in the source tree and add a suffix, such as .in to it. This will allow us to process the file during the build to customize the Exec entry without the risk of overwriting the source file.

Utilizaremos una directiva simple CMake para realizar la personalización e instalaciónn. Puesto que el prefijo de instalación no lo conoceremos hasta el momento de la construcción, necesitamos ajustar ligeramente nuestro servicio de fichero. Using the myapp example again, we might create a file called org.kde.myapp.service that contains the following content:

[D-BUS Service] Name=org.kde.myapp Exec=@CMAKE_INSTALL_PREFIX@/bin/myapp

En el fichero CMakeLists.txt añadiremos estas dos líneas:

include(DBusMacros) dbus_add_activation_service(org.kde.myapp.service.in)

As of CMake 2.6.1, this macro does not exist natively. To make it exist, you can place this CMake module file in the cmake/ directory of your application, and then you can use the above command.

Por ejemplo, si tu aplicación está en algún lugar en kdebase/workspace, you have to make sure that this cmake module file (which is linked above), exists at kdebase/workspace/cmake/modules/PkgConfigGetVar.cmake.

Cuando se ejecuta make install, a properly formed service file will be generated (using the .service file that you have just created), and installed to the correct location on disk. Tu aplicación está ahora preparada para ser activada automáticamente cuando se necesite.