The new emerging NLE for GNU/Linux
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This page was moved from Cehteh's MoinMoin-wiki, which at that time was the first home of Lumiera development
The design and techniques outlined here are in use without major changes as of 2015 (and can be expected to remain this way). The documentation needs rewording in a more neutral and descriptive way and probably an introductory paragraph might be helpful TODO

…There is now sort-of an “application realm”, which doesn’t belong strictly to any one of the Layers. It serves the purpose of pulling up and tearing down the application in a controlled fashion. And additionally, it provides the Interface and Config core services. Within the application, we find a small number of Subsystems, which are more or less independent. These subsystems are conceptual entities and don’t correspond 1:1 to a layer, an interface, a class or a plugin. These subsystems are of no relevance outside the mentioned "application realm". When the application is in normal operational mode, we have the usual components, interfaces, services, aggregated into the three Layers.

Currently I’ve identified the following subsystems:

  • Engine

  • Builder

  • Session

  • Lumiera GUI

  • Script runner

  • Renderfarm node server

To deal with those subsystems, I’ve created an Interface to define the operations and liabilities of a subsystem. Additionally, I assume that for each subsystem there is a Façade, which the subsystem is free to implement as it sees fit. Typically, this façade will load plugins, register and provide further "business interfaces", and especially set up the Layer separation interfaces which canalise any communication going on between the layers.

Tip The code from my startup branch has meanwhile been merged to master. Look here for the code referred in the following discussion.
  • common/subsys.hpp contains the subsystem interface mentioned above.

  • lumiera/main.cpp uses the subsystem instances provided by the facades, and additionally the services of lumiera::AppState (common/appstate.hpp)

  • AppState represents the state as relevant for the "application realm", i.e. it performs global initialisation and shutdown. See especially AppState::init()

  • see backend/enginefacade.hpp|cpp as an (unimplemented) façade skeleton. backend::EngineFacade::getDescriptor() yields the subsystem interface

  • the GuiFacade is somewhat special, because we want to load the GUI from a shared library. This façade is basically completed and working, but it currently just loads a dummy plugin. The implementation of the GuiFacade needs to be in core (because it pulls the plugin); that’s why I’ve put it into common/guifacade.cpp, while the interface is in gui/guifacade.hpp as usual.

  • as an example for a Layer separation interface, I’ve implemented the GuiNotificationFacade, which will be used by the lower layers to push informations into the GUI (and finally to request the GUI to shut down). Layer separation interfaces are considered part of the public Lumiera API, thus the headers go into src/include/**

    • include/guinotification.h (C/C combined header) defines an C interface (abstract class) and a CLI interface.

    • embedded into the interface is a factory, i.e. by gui::GuiNotification::facade() you get an instance…

    • which actually is a proxy and routes any call through the instance of the accompanying CLI interface which is defined within the interface/plugin system

    • this in turn forwards to the implementation class in gui/guinotificationfacade.cpp, which is assumed to live within the GUI (shared lib)


Actually this system builds on the assumption, that starting each subsystem doesn’t block the overall start/main/stop thread. I.e. any subsystem is supposed to spawn its control/event threads if necessary. Not every subsystem needs to spawn threads though (for example, the session doesn’t). In the current implementation no spawning of threads happens. Likewise, I’ve commented out the synchronisation primitives.
TODO 2015 meanwhile we do spawn threads and perform synchronisation

Initialisation and Lifecycle

Basically, everything workes as discussed last spring in the GlobalInitialisation design entry. I’ve considered to switch to simple functions pre_init(), init(), … as proposed by Cehteh, but I’m not happy with this idea, because it creates a coupling between anything which needs to be done in a certain initialisation function. Actually, I prefer the usual approach of lifecycle events (or signals) used in many application frameworks, i.e. the publisher-subscriber model. This allows to keep the registration immediately within the implementation of a facility, and it allows to add an arbitrary number of additional lifecycle events, like ON_SESSION_CLOSE, ON_BUILD, ON_EMERGENCY_EXIT.

Basically we have now the following steps and events happening

  • ON_BASIC_INIT runs "somewhere" in the static initialisation phase before main(). To schedule something there, you need to place a statc C++ variable. This should be reserved for very basic initialisation tasks which need to be done even prior to any global initialisation, e.g. the NOBUG_INIT is done this way, the config system, maybe setting up a dispatcher table based on (compile time) type information (for the rules engine).

  • AppState::init() cares for bringing up the plugin loader and opens the config-interface.

  • …followed by triggering ON_GLOBAL_INIT

  • main() pulls up the subsystems according to the command line options.

  • within each subsystem, façade interfaces shall be opened with the interface system. Any initialisation of components should be tied to these.

  • as a rule and if possible, any service should be written such as to come up on demand.

  • shutdown or failure of any given subsystem initiates the shutdown sequence by requesting all other running subsystems to terminate

  • there is an ON_GLOBAL_SHUTDOWN event, which can be used for normal cleanup. In case of an emergency exit, this hook may be skipped

  • alternatively, the ON_EMERGENCY_EXIT event is triggered. In case of nested exceptions, this may happen twice.

  • the AppState destructor tries to bring down the core systems (config-interface and pluginloader).

Demo Run

  • building with scons (default target) now yields a bin/, besides the bin/lumiera exe the scons built created since day one.

  • we need to set the LUMIERA_PLUGIN_PATH from the commandline to point to this bin directory, e.g.

  • LUMIERA_PLUGIN_PATH=/home/hiv/devel/lumi/.libs NOBUG_LOG='test:TRACE,lumiera:TRACE,config:TRACE' bin/lumiera 2>&1 | egrep -v '(TODO)|(FIXME)'

00000392: configfacade.cpp:74: INFO: thread_1: Config: Config system ready.
00000394: main.cpp:55: NOTICE: thread_1: main: *** Lumiera NLE for Linux ***
00000395: appstate.cpp:114: TRACE: thread_1: init: initialising application core...
00000405: interface.c:54: TRACE: thread_1: lumiera_interface_open: lumieraorg_interface
00000406: interface.c:55: WARNING: thread_1: lumiera_interface_open: opening experimental interface: lumieraorg_interface_0_lumieraorg_interface
00000412: interface.c:168: TRACE: thread_1: lumiera_interface_open_interfacenode: lumieraorg_interface 0 ()
00000437: config.c:199: NOTICE: thread_1: lumiera_config_get: envvar override for config LUMIERA_PLUGIN_PATH = /home/hiv/devel/lumi/
00000444: config.c:199: NOTICE: thread_1: lumiera_config_get: envvar override for config LUMIERA_PLUGIN_PATH = /home/hiv/devel/lumi/
00000467: appstate.cpp:132: TRACE: thread_1: init: Lumiera core started successfully.
00000469: appstate.cpp:140: TRACE: thread_1: maybeStart: maybe startup Builder...?
00000472: appstate.cpp:140: TRACE: thread_1: maybeStart: maybe startup Renderfarm node...?
00000475: appstate.cpp:140: TRACE: thread_1: maybeStart: maybe startup Lumiera GTK GUI...?
00000476: subsystemrunner.hpp:144: INFO: thread_1: triggerStartup: Starting subsystem "Lumiera GTK GUI"
00000477: interface.c:54: TRACE: thread_1: lumiera_interface_open: lumieraorg_GuiStarterPlugin
00000483: interface.c:168: TRACE: thread_1: lumiera_interface_open_interfacenode: lumieraorg_GuiStarterPlugin 0 ()
 *** Ha Ha Ha
     this is the GuiStarterPlugin speaking!
     now, the Lumiera GUI should be spawned....
     but actually nothing happens!!!!!!!!!!!!!!
00000491: appstate.cpp:140: TRACE: thread_1: maybeStart: maybe startup Script runner...?
00000494: appstate.cpp:171: NOTICE: thread_1: maybeWait: Shutting down Lumiera...
00000495: interface.c:230: TRACE: thread_1: lumiera_interface_close:
00000498: interface.c:258: TRACE: thread_1: lumiera_interfacenode_close: lumieraorg_GuiStarterPlugin 1 ()
00000634: configfacade.cpp:83: TRACE: thread_1: ~Config: config system closed.
00000635: appstate.cpp:245: TRACE: thread_1: ~AppState: shutting down basic application layer...
00000643: interface.c:230: TRACE: thread_1: lumiera_interface_close:
00000646: interface.c:258: TRACE: thread_1: lumiera_interfacenode_close: lumieraorg_interface 1 ()
  • incidentally, running… lumiera --help produces the following output

00000392: configfacade.cpp:74: INFO: thread_1: Config: Config system ready.
00000394: main.cpp:55: NOTICE: thread_1: main: *** Lumiera NLE for Linux ***
Lumiera, the non linear video editor. Supported parameters:
  -h [ --help ]         produce help message
  -f [ --session ] arg  session file to load (UNIMPLEMENTED)
  -s [ --script ] arg   execute the given LUA script (UNIMPLEMENTED)
  --headless            start without GUI
  -p [ --port ] arg     open renderfarm node at given port (UNIMPLEMENTED)
  -d [ --define ] arg   enter definition into config system (UNIMPLEMENTED)