[LAD] JACK latency API clarifications

Paul Davis paul at linuxaudiosystems.com
Fri Feb 21 14:51:46 UTC 2014

On Fri, Feb 21, 2014 at 9:38 AM, Stefano D'Angelo <zanga.mail at gmail.com>wrote:

> Sorry guys, other two (silly?) questions:
> 1. apart from the process callback, which callbacks need to be
> RT-safe? Looking around I found a master thesis [1] that says: "Apart
> from
> the JackProcessCallback callback, which is called in the realtime
> audio thread for obvious reasons, all other callbacks are called
> asynchronously in a specialized non-realtime thread, to avoid
> notifications to interfere with audio processing", is that true?

The documentation does actually state which ones need to be RT, but there
is no list to easily consult.

The threading design described above is specific to Jack2. Jack1 delivers
all callbacks to the same thread (which necessarily means that processing
audio is blocked by other callbacks). This is one of the major (and largely
hidden) design differences between Jack1 and Jack2.

> 2. may the system sample rate actually change (while a client is running)?

JACK to date has never supported changing the sample rate.
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