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+Overview
+This software implements D-Bus endpoint for JACK server.
Brief History
+Initial version of jackdbus was created +as part of LADI project and was ad-hoc modification of JACK1 codebase. +jackdbus for JACK1 was maintained first as a setup of ad-hoc patches, +then via Mercural and then via Git. +In 2008/2009, jackdbus was ported to jackdmp codebase along with an implementation +of the newly designed for the new need control API for JACK. +The result of this merge became known as +JACK2. +As of 2022, jackdbus is again maintained in LADI project. +The jackaudio.org version of jackdbus is considered older/alternative +implementation.
For LADI specific issues, submit issues or pull request to LADI project. +For related discussions, you are invited to join +Libera.Chat channel #ladi
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+Do not submit LADI specific issues to jackaudio project. | +
D-Bus access
+D-Bus is an object model that provides IPC mechanism. +D-Bus supports autoactivation of objects, +thus making it simple and reliable to code a "single instance" application or daemon, +and to launch applications and daemons on demand when their services are needed.
Improvements over classical "jackd" approach:
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+Simplified single thread model for control and monitor + applications. Various D-Bus language bindings make it trivial to + write control and monitor applications using scripting languages + like Python, Ruby, Perl, etc.. +
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+A log file is available for inspection even when autoactivation + happens by the first launched JACK application. +
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+A real configuration file is used to persist settings to be + manipulated through configuration interface of JACK D-Bus object. +
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+Improved graph inspection and control mechanism. JACK graph is + versioned. Connections, ports and clients have unique + (monotonically increasing) numeric IDs. +
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+High level abstraction of JACK settings. Allows applications that + can configure JACK to expose parameters that were not known at + compile (or tarball release) time. Recent real world examples are + the JACK MIDI driver parameters and support for FFADO driver in + QJackCtl. Upgrading of JACK requires upgrade of QJackCtl in order + to make new settings available in the GUI. +
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How it works
+Autoactivation and starting/stopping JACK server
+First, application that issues D-Bus method call to JACK controller object, +causes D-Bus session daemon to activate the object by starting the jackdbus executable. +Activating controller object does not start the server. +Instead controller object has several interfaces. +The most important of them is the control interface. +Control interface contains methods for starting and stopping JACK server, +loading and unloading of internal clients (netjack), +setting buffer size and resetting xrun counter. +It also contains methods for querying information required by monitoring +applications:
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+whether JACK server is started +
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+whether JACK server is running in realtime mode +
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+sample rate +
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+DSP load +
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+current buffer size +
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+latency +
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+xrun counter +
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JACK server autostart is achieved by libjack calling "jack server start" method of +JACK control D-Bus interface.
JACK settings
+Applications that want to manage JACK settings can query +and set all settings that were traditionally specified as +jackd command-line parameters. +Interface abstraction provides virtual tree of parameter +containers with container leaves that contain parameters. +Parameters are accessed using simple addressing scheme (array of strings) +where address defines path to parameter, like "drivers", "alsa", "dither".
Overview of the tree of standard settings' addresses:
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+"engine" +
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+"engine", "driver" +
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+"engine", "realtime" +
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+"engine", …more engine parameters +
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+"driver", "device" +
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+"driver", …more driver parameters +
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+"drivers", "alsa", "device" +
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+"drivers", "alsa", …more alsa driver parameters +
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+"drivers", …more drivers +
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+"internals", "netmanager", "multicast ip" +
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+"internals", "netmanager", …more netmanager parameters +
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+"internals", …more internals +
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JACK settings are persisted. +I.e. they are automatically saved by jackdbus when they are set. +Next time user starts JACK server, last saved settings will be automatically used. +Changing JACK settings through the configure D-Bus interface takes effect on next +JACK server start. +On the fly change of the buffer size, as available in the libjack +(jack.h) API, is also possible through the control D-Bus interface.
JACK parameter constraints
+JACK internal modules that provide parameters visible through control API can provide +information about parameter valid range (like realtime priority) or +whether parameter should be presented as enumeration. +Enumeration parameters can be strict and non-strict. +Example of strict enum parameter is dither parameter of ALSA driver, +it has only predefined valid values: "shaped noise", +"rectangular", "triangualr" and "none".
Example of non-strict parameter is device parameter of ALSA driver. +It is useful to provide some detected device strings as choices to user, +but still allow user to specify custom string that ALSA layer is supposed to +understand.
JACK patchbay
+In order to simplify patchbay applications, extended functionality is provided. +There is a method that returns the current graph state. +Graph state has unique monotonically increasing version number +and contains info about all clients, their ports and connections. +Connections, ports and clients have unique numeric IDs +that are guaranteed not to be reused. +Notifica tions about graph changes are provided using +D-Bus signals.
JACK D-Bus enabled applications
+jack_control
+JACK contains "jack_control" executable, a 300 lines of Python exposing +JACK D-Bus functionality. It allows chained execution of several commands. +For example "jack control ds alsa dps midi-driver raw eps realtime on +eps relatime-priority 70 start" selects ALSA driver, enables JACK MIDI +raw backend, enables realtime mode, sets realtime priority to 70 and starts +JACK server.
LADI Tools
+LADI Tools is a set of programs to configure, control and monitor JACK. +It provides tray icon, Window Maker style dockapp, +G15 keyboard LCD display integration application, +configuration utility for managing JACK settings +and log file monitor application.
All tools are written in Python.
Patchage
+Patchage, the ubiquitous canvas modular patch bay can be compiled to use +D-Bus instead of libjack to communicate with JACK.
Doing so also enables JACK server start/stop functionality in Patchage.
Various JACK related features are implemented:
LADI Session handler (LADISH)
+LADISH, a rewrite of LASH session handler +uses D-Bus to communicate with JACK.
Various JACK related features are implemented:
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+Saving of JACK settings as part of "studio" session. +
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+Handling of "JACK server crash" scenario: restarting JACK server, +notifying JACK applications that JACK server reappeared so they +can reconnect to it, and restoring JACK connections. +
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QjackCtl JACK Audio Connection Kit - Qt GUI Interface
+QjackCtl is a simple Qt application +to control the JACK sound server daemon, is another jackdbus frontend.
KXStudio Cadence
+Cadence, a set of tools +useful for audio production, is another jackdbus frontend.
Studio Controls
+Studio Controls, a way to +configure your Linux-based audio installation for real-time audio, is +another jackdbus frontend.
References
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