JACK2 aka jackdmp is a C++ version of the JACK low-latency audio server for multi-processor machines. It is a new implementation of the JACK server core features that aims at removing some limitations of the JACK1 design. The activation system has been changed for a data flow model and lock-free programming techniques for graph access have been used to have a more dynamic and robust system.
- uses a new client activation model, that allows simultaneous client execution (on a SMP machine) when parallel clients exist in the graph (client that have the same inputs). This activation model allows to better use available CPU on a smp machine, but also works on mono-processor machine.
- uses a lock-free way to access (read/write) the client graph, thus allowing connections/disconnection to be done without interrupting the audio stream. The result is that connections/disconnections are glitch-free.
- can work in two different modes at the server level:
- synchronous activation: in a given cycle, the server waits for all clients to be finished (similar to normal jackd)
- asynchronous activation: in a given cycle, the server does not wait for all clients to be finished and use output buffer computed the previous cycle. The audible result of this mode is that if a client is not activated during one cycle, other clients may still run and the resulting audio stream will still be produced (even if its partial in some way). This mode usually result in fewer (less audible) audio glitches in a loaded system.
For further information, see the JACK homepage and wiki. There are also the #jack and #lad chat channels on freenode IRC.