# Client Callbacks

## Functions

int | jack_set_thread_init_callback (jack_client_t *client, JackThreadInitCallback thread_init_callback, void *arg)
void | jack_on_shutdown (jack_client_t *client, void(*function)(void *arg), void *arg)
int | jack_set_process_callback (jack_client_t *client, JackProcessCallback process_callback, void *arg)
int | jack_set_freewheel_callback (jack_client_t *client, JackFreewheelCallback freewheel_callback, void *arg)
int | jack_set_buffer_size_callback (jack_client_t *client, JackBufferSizeCallback bufsize_callback, void *arg)
int | jack_set_sample_rate_callback (jack_client_t *client, JackSampleRateCallback srate_callback, void *arg)
int | jack_set_client_registration_callback (jack_client_t *, JackClientRegistrationCallback registration_callback, void *arg)
int | jack_set_port_registration_callback (jack_client_t *, JackPortRegistrationCallback registration_callback, void *arg)
int | jack_set_port_connect_callback (jack_client_t *, JackPortConnectCallback connect_callback, void *arg)
int | jack_set_graph_order_callback (jack_client_t *, JackGraphOrderCallback graph_callback, void *)
int | jack_set_xrun_callback (jack_client_t *, JackXRunCallback xrun_callback, void *arg)

## Function Documentation

void jack_on_shutdown | ( | jack_client_t * | client,
|  | void(*)(void *arg) | function,
|  | void * | arg |
| ) |  |  |

Parameters:

  | client | pointer to JACK client structure.
  | function | The jack_shutdown function pointer.
  | arg | The arguments for the jack_shutdown function.

Register a function (and argument) to be called if and when the JACK server shuts down the client thread. The function must be written as if it were an asynchonrous POSIX signal handler --- use only async-safe functions, and remember that it is executed from another thread. A typical function might set a flag or write to a pipe so that the rest of the application knows that the JACK client thread has shut down.

NOTE: clients do not need to call this. It exists only to help more complex clients understand what is going on. It should be called before jack_client_activate().

Referenced by main().

int jack_set_buffer_size_callback | ( | jack_client_t * | client,
|  | JackBufferSizeCallback | bufsize_callback,
|  | void * | arg |
| ) |  |  |

Tell JACK to call bufsize_callback whenever the size of the the buffer that will be passed to the process_callback is about to change. Clients that depend on knowing the buffer size must supply a bufsize_callback before activating themselves.

Parameters:

  | client | pointer to JACK client structure.
  | bufsize_callback | function to call when the buffer size changes.
  | arg | argument for bufsize_callback.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_client_registration_callback | ( | jack_client_t * | ,
|  | JackClientRegistrationCallback | registration_callback,
|  | void * | arg |
| ) |  |  |

Tell the JACK server to call registration_callback whenever a port is registered or unregistered, passing arg as a parameter.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_freewheel_callback | ( | jack_client_t * | client,
|  | JackFreewheelCallback | freewheel_callback,
|  | void * | arg |
| ) |  |  |

Tell the Jack server to call freewheel_callback whenever we enter or leave "freewheel" mode, passing arg as the second argument. The first argument to the callback will be non-zero if JACK is entering freewheel mode, and zero otherwise.

Returns:
  0 on success, otherwise a non-zero error code.

int jack_set_graph_order_callback | ( | jack_client_t * | ,
|  | JackGraphOrderCallback | graph_callback,
|  | void * |  |
| ) |  |  |

Tell the JACK server to call graph_callback whenever the processing graph is reordered, passing arg as a parameter.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_port_connect_callback | ( | jack_client_t * | ,
|  | JackPortConnectCallback | connect_callback,
|  | void * | arg |
| ) |  |  |

Tell the JACK server to call connect_callback whenever a port is connected or disconnected, passing arg as a parameter.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_port_registration_callback | ( | jack_client_t * | ,
|  | JackPortRegistrationCallback | registration_callback,
|  | void * | arg |
| ) |  |  |

Tell the JACK server to call registration_callback whenever a port is registered or unregistered, passing arg as a parameter.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_process_callback | ( | jack_client_t * | client,
|  | JackProcessCallback | process_callback,
|  | void * | arg |
| ) |  |  |

Tell the Jack server to call process_callback whenever there is work be done, passing arg as the second argument.

The code in the supplied function must be suitable for real-time execution. That means that it cannot call functions that might block for a long time. This includes malloc, free, printf, pthread_mutex_lock, sleep, wait, poll, select, pthread_join, pthread_cond_wait, etc, etc. See http://jackit.sourceforge.net/docs/design/design.html#SECTION00411000000000000000 for more information.

Returns:
  0 on success, otherwise a non-zero error code, causing JACK to remove that client from the process() graph.

Referenced by jack_initialize(), and main().

int jack_set_sample_rate_callback | ( | jack_client_t * | client,
|  | JackSampleRateCallback | srate_callback,
|  | void * | arg |
| ) |  |  |

Tell the Jack server to call srate_callback whenever the system sample rate changes.

Returns:
  0 on success, otherwise a non-zero error code

int jack_set_thread_init_callback | ( | jack_client_t * | client,
|  | JackThreadInitCallback | thread_init_callback,
|  | void * | arg |
| ) |  |  |

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.

Returns:
  0 on success, otherwise a non-zero error code, causing JACK to remove that client from the process() graph.

int jack_set_xrun_callback | ( | jack_client_t * | ,
|  | JackXRunCallback | xrun_callback,
|  | void * | arg |
| ) |  |  |

Tell the JACK server to call xrun_callback whenever there is a xrun, passing arg as a parameter.

Returns:
  0 on success, otherwise a non-zero error code