Using the Qt booster

This section describes how to use the Qt booster. The booster provides the application with the key libraries already present in the process, but no other initialisations are done in the booster.

Prerequisites

The launcher can start an application if the following prerequisites are met:

• The application is compiled and linked to a position independent binary (executable or library)

• The application is started with the invoker command instead of executing the executable file.

1. Compiling and linking for launcher

If you intend to run a binary with applauncherd, compile it with -fPIC option to produce position-independent code. It is recommended that you link them either as shared libraries, or, preferably, as position-independent executables, which can be executed both traditionally and with the launcher. The -pie and -rdynamic linker flags accomplish this.

To improve linking and loading times of shared object libraries, it is recommended that you hide any unnecessary symbols from the resulting binary by using -fvisibility=hidden and -fvisibility-inlines-hidden flags as well. However, applauncherd needs to find the entry point for your application, so the symbol main needs to be explicitly made visible. This can be done as follows:

  #include <QtCore/QtGlobal>
  
  Q_DECL_EXPORT int main(int argc, char **argv)
  {
  ...
  }

If your application loads a plug-in that needs to access some symbols in the main application, the symbols also need to be exported. In addition, you must use the --global-syms invoker parameter, as described in Advanced invoker command line parameters.

Normally you do not need to worry about the compiler and linker flags, as the applauncherd-dev package provides configuration options for qmake, CMake, and pkg-config. If you are building a Debian package, make your package build-depend on applauncherd-dev and your application binary package depend on applauncherd.

For details on how to get the compiler and linker flags, see Using qmake, Using CMake, or Using pkg-config.

2. Adapting application source code

No modifications are typically needed when the Qt booster is used. However, if the application has explicit calls to exit(), change them to use _exit() instead. This prevents cleanup actions related to shared libraries to be performed multiple times. For more details, see Limitations and known issues.

3. Launching the application

Check that applauncherd package is installed and applancherd daemon is running. You can now run your application as usual as /usr/bin/myApp, or use the qtboosted launching by running:

invoker --type=q /usr/bin/myApp

4. Finishing touches

The invoker can also provide single instance behaviour and a splash screen for your application as follows. For more details, see Enabling single instance support for an application and Enabling a splash screen for an application.

/usr/bin/invoker --single-instance --splash=/usr/share/myApp/splash.jpg --type=q /usr/bin/myApp