[LAD] xrun callback

Hello, I'm trying to use jack_set_xrun_callback to be notified in my application of eventual xrun. in the documentation of the function I see a note: that 'this function cannot be called while the client is activated'. Does it mean that my client must call jack_set_xrun_callback before being activated or that the callback cannot be called while client is activated? If it's the later than should I use another client that will stay not activated as parameter jack_client_t It says return 0 on success. Does it mean the callback must succeed doing something or can it just increase some counter and return 0. What would be the consequences of a non-zero error code? Would jack stop? Currently I'm registering the callback and then activate and use the client. I'm not sure if I get an xrun that does crash my application of if something wrong in the application makes it crash and trigger an xrun... Chicken and egg problem. Is there another way? Thanks -- Raphaël. for reference: from jack.h /** * Tell the JACK server to call @a xrun_callback whenever there is a * xrun, passing @a arg as a parameter. * * All "notification events" are received in a seperated non RT thread, * the code in the supplied function does not need to be * suitable for real-time execution. * * NOTE: this function cannot be called while the client is activated * (after jack_activate has been called.) * * @return 0 on success, otherwise a non-zero error code */ int jack_set_xrun_callback (jack_client_t *client, JackXRunCallback xrun_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;