/*! \page technical Technical Overview

!! TODO: Do something to this mess !!

In Harmattan, the applauncherd daemon is started by UpStart as part of
XSession, that is, at the same level as the desktop (MeeGo Touch
homescreen). In MeeGo, applaucherd is started by uxlaunch which is the
program that brings up X and the ui.

Applauncherd forks will-be-application processes, "boosters", before knowing
which application is going to be launched next. Different boosters are
optimized for different kinds of applications, e.g. Qt, Meego Touch, Qt
Declarative.  Boosters are loaded as plugins. Applauncherd searches for plugin
libraries in /usr/lib/applaucherd/lib*booster.so and forks a new process for
each booster to wait for launch commands from the user.

The user uses the launcher always through a special invoker program. The
invoker (/usr/bin/invoker) uses a socket connection to tell a booster process
to load an application binary.

In addition to possible source code changes, an application which is to be used
with applauncherd must be compiled as a shared library or a position
independent executable (-pie) and it must always export main().

Before loading an application binary, a booster process changes its security
credentials so that the code in the application binary will be executed with
the correct credentials. The process also sets environment variables to the
values sent by the invoker. Loading the binary is done with dlopen(), and
therefore the application needs to be compiled and linked as a shared library
or a position independent executable. Finally, the booster process finds the
main function in the application binary with dlsym() and calls the main() with
the command line arguments given by the invoker.

The launcher itself is a library that is loaded by a small C-program (/usr/bin/applauncherd.bin).
The idea behind this is to avoid linking the launcher binary to any
libraries. This gives full control over the flags with which the preloaded
libraries are opened with dlopen(). 

In Harmattan, Aegis platform security is used to protect the socket connection
between the invoker and boosters. This works only for ARM target. It is
automatically disabled by the build scripts when compiling on x86.

Each application type (currently Qt, Qt Declarative and MeeGo Touch) has its own booster process.
When booster launches the application by calling the "main()" function,
applauncherd will create new booster process of that type.

Booster processes do some initializations that cannot be shared among other
processes and therefore have to be done after forking. This allows, for instance,
instantiating an MApplication (QApplication) before knowing the name of the
application. Then the booster process waits for a connection from the invoker with
the information about which application should be launched. 

With MeeGo Touch booster and Qt Declarative booster, applications can fetch certain objects from a cache. 
This will significantly reduce the startup time of an application. 

*/