JACK 0.120.1 released

JACK 0.120.1 represents more than a year of incremental development on JACK1. The majority of the work has been done by Torben Hohn, and includes one major API revision and one major API addition, along with a quite a few other fixes, API clarifications and new utilities.

The addition is the new Session API that allows for easy management (save/restore) of multi-client configurations. The core JACK release does not include a session management application, but QJackctl already offers this. The session API has already been implemented in Jack2. Please see below for links to read about this API.

The revision involves the API used to manage and discover latency in JACK signal flow, and unlike the existing one (now marked as deprecated)), this one can actually do what it needs to do. Anyone who has written a client that used the existing port latency API should update their client to use the new one: the old API will be removed when we move to API/protocol version 1.0.0 which will be soon.

Please note that the latency API has not been implemented in Jack2 at this time.

Usage Changes

• add -M command line flag to allow user-specified MIDI buffer sizing The units of the argument to this command line flag are "MIDI events per process() cycle", where an event occupies up to 4 bytes (as most common MIDI events do). The default buffer size is same as the one used for audio data, which will store about 2 MIDI events per sample. Typical values for event-count will range from 10 to about 500. Be aware that using very high values along with a large number of ports may cause JACK to fail to start because of the amount of memory that would be required.
• several new utility clients:
  • jack_midi_dump (Carl Hetherington) (displays MIDI events arriving at its input port as text in its originating terminal window)
  • jack_iodelay (from the original jdelay in C++ by Fons Adriensen; ported to C by Torben Hohn)
  • jack_latent_client (for testing latency API)
  • jack_session_notify (a minimal session manager)

Developer-visible Changes

Applications can now request weak linkage for all function symbols in the JACK API. See http://jackaudio.org/files/docs/html/group__WeakLinkage.html for more information.

Using Port Buffers before activating a client

It has always been undefined behaviour to try to use JACK port buffers outside of a process callback. This release adds an additional limitation: any call to jack_port_get_buffer() before jack_activate() will return NULL rather than a usable address. This may cause issues in clients which did this - the behaviour was always wrong, but was not enforced by JACK.

Determining and tracking port buffer sizes

A few details about detecting the port buffer sizes have changed:

• clients should now use jack_port_type_get_buffer_size() if they absolutely must determine buffer sizes before they call jack_activate(). The use of jack_port_get_buffer_size() before calling jack_activate() is now forbidden and may result in the client crashing.
• clients that care about port buffer sizes should register a buffer size callback. The callback will now always be executed during a call to jack_activate(). This ensures that on return from jack_activate() and before the first call to its process callback, the client definitely knows the buffer size. Future callbacks will occur if the buffer size changes. Note that older versions of JACK do not necessarily call the buffer size callback during jack_activate() - this behaviour should be considered a serious bug in JACK and another reason to upgrade.

Session API

JACK Session is a new section of the JACK API that is designed to allow management of JACK configurations that involve multiple clients. Use of the API is optional by clients, but is strongly recommended.

The API is fully documented online:

• API Reference: http://jackaudio.org/files/docs/html/group__SessionClientFunctions.html
• Walkthrough for client developers: http://trac.jackaudio.org/wiki/WalkThrough/Dev/JackSession

Latency API

The older latency management API is now deprecated because it was fundamentally broken (in the sense that it could not do what it claimed to be able to do)

The new API is fully documented online

• API Reference: http://jackaudio.org/files/docs/html/group__LatencyFunctions.html
• Conceptual diagram: http://jackaudio.org/files/jack-latency.png

Bug Fixes, Tweaks Etc. Etc

• switch all example clients and tools to use jack_client_open()
• README emptied to just point at http://jackaudio.org/
• replace use of pthread_t in public headers with jack_native_thread_t
• offer build time option to make code 100% valgrind clean
• shm.c released under LGPL, not GPL, to match the rest of libjack
• fixes for rare crashes in alsa_in/out
• netjack1 support for Celt 0.9
• check arguments given to jack_bufsize, to prevent server lockup
• check arguments to jack_set_buffer_size() in server
• jack_connect can use client UUIDs
• sanitycheck now no longer warms about unlimited lockable memory
• sanitycheck no longer mentions nice
• fix race conditions near client exit/shutdown/zombiefication
• no watchdog operations while freewheeling (JACK will no longer die if freewheeling is very, very slow)
• (incomplete) new internal client code based on a2jmidid (originally by Dmitry Baikov & Nedko Arnaudov)