Controlling & querying JACK server operation

Functions
int	jack_set_freewheel (jack_client_t *client, int onoff) JACK_OPTIONAL_WEAK_EXPORT
int	jack_set_buffer_size (jack_client_t *client, jack_nframes_t nframes) JACK_OPTIONAL_WEAK_EXPORT
jack_nframes_t	jack_get_sample_rate (jack_client_t *) JACK_OPTIONAL_WEAK_EXPORT
jack_nframes_t	jack_get_buffer_size (jack_client_t *) JACK_OPTIONAL_WEAK_EXPORT
int	jack_engine_takeover_timebase (jack_client_t *) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT
float	jack_cpu_load (jack_client_t *client) JACK_OPTIONAL_WEAK_EXPORT

Detailed Description

Function Documentation

float jack_cpu_load

(

jack_client_t *

client

)

Returns

the current CPU load estimated by JACK. This is a running average of the time it takes to execute a full process cycle for all clients as a percentage of the real time available per cycle determined by the buffer size and sample rate.

int jack_engine_takeover_timebase

(

jack_client_t *

)

Old-style interface to become the timebase for the entire JACK subsystem.

Deprecated:

This function still exists for compatibility with the earlier transport interface, but it does nothing. Instead, see transport.h and use jack_set_timebase_callback().

Returns

ENOSYS, function not implemented.

jack_nframes_t jack_get_buffer_size

(

jack_client_t *

)

Returns

the current maximum size that will ever be passed to the process_callback. It should only be used before the client has been activated. This size may change, clients that depend on it must register a bufsize_callback so they will be notified if it does.

See also

jack_set_buffer_size_callback()

jack_nframes_t jack_get_sample_rate

(

jack_client_t *

)

Returns

the sample rate of the jack system, as set by the user when jackd was started.

Referenced by main().

int jack_set_buffer_size	(	jack_client_t *	client,
		jack_nframes_t	nframes
	)

Change the buffer size passed to the process_callback.

This operation stops the JACK engine process cycle, then calls all registered bufsize_callback functions before restarting the process cycle. This will cause a gap in the audio flow, so it should only be done at appropriate stopping points.

See also

jack_set_buffer_size_callback()

Parameters

client	pointer to JACK client structure.
nframes	new buffer size. Must be a power of two.

Returns

0 on success, otherwise a non-zero error code

int jack_set_freewheel	(	jack_client_t *	client,
		int	onoff
	)

Start/Stop JACK's "freewheel" mode.

When in "freewheel" mode, JACK no longer waits for any external event to begin the start of the next process cycle.

As a result, freewheel mode causes "faster than realtime" execution of a JACK graph. If possessed, real-time scheduling is dropped when entering freewheel mode, and if appropriate it is reacquired when stopping.

IMPORTANT: on systems using capabilities to provide real-time scheduling (i.e. Linux kernel 2.4), if onoff is zero, this function must be called from the thread that originally called jack_activate(). This restriction does not apply to other systems (e.g. Linux kernel 2.6 or OS X).

Parameters

client	pointer to JACK client structure
onoff	if non-zero, freewheel mode starts. Otherwise freewheel mode ends.

Returns

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