proper jack_set_thread_init_callback behavior

[wmedrano]

The documentation says:

Tell JACK to call thread_init_callback once just after the creation of the thread in which all other callbacks will be handled.

The code in the supplied function does not need to be suitable for real-time execution.

However, in jack and jack2 I've noticed that it gets called multiple times.

Simple program that has has callback called multiple times. https://pastebin.com/dVZqdGdh

Should the documentation be updated? I think saying creation of the thread implies that there is a single thread and the function will be called only once.

RustAudio/rust-jack#104

[HadrienG2]

Could it be because jack2, which uses multiple audio processing threads, actually spawns multiple audio threads per application? I just checked that the different invocations come from different OS threads...

If so, that is indeed just a matter of clarifying the documentation.

[emmef]

Seeing the above, is my assumption correct that jack_set_thread_init_callback(...) only calls thread_init_callback for threads that also call process_callback as set by jack_set_process_callback(...)? In that case, the documentation could be clarified as:

Tell JACK to call thread_init_callback once just after the creation of a processing thread in which processing callbacks will be handled.