jack2/common/jack.h

/*
  Copyright (C) 2001 Paul Davis
  Copyright (C) 2004 Jack O'Quin
  
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.
  
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU Lesser General Public License for more details.
  
  You should have received a copy of the GNU Lesser General Public License
  along with this program; if not, write to the Free Software 
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

  $Id: jack.h,v 1.5.2.6 2006/06/20 14:44:00 letz Exp $
*/

#ifndef __jack_h__
#define __jack_h__

#ifdef __cplusplus
extern "C"
{
#endif

#ifdef WIN32
	#include <windows.h>
    typedef HANDLE pthread_t;
#else
	#include <pthread.h>
#endif

/*
#include <jack/types.h>
#include <jack/transport.h>
*/

#include "types.h"
#include "transport.h"

    /**
     * Note: More documentation can be found in jack/types.h.
     */

    /**
     * Open an external client session with a JACK server.  This interface
     * is more complex but more powerful than jack_client_new().  With it,
     * clients may choose which of several servers to connect, and control
     * whether and how to start the server automatically, if it was not
     * already running.  There is also an option for JACK to generate a
     * unique client name, when necessary.
     *
     * @param client_name of at most jack_client_name_size() characters.
     * The name scope is local to each server.  Unless forbidden by the
     * @ref JackUseExactName option, the server will modify this name to
     * create a unique variant, if needed.
     *
     * @param options formed by OR-ing together @ref JackOptions bits.
     * Only the @ref JackOpenOptions bits are allowed.
     *
     * @param status (if non-NULL) an address for JACK to return
     * information from the open operation.  This status word is formed by
     * OR-ing together the relevant @ref JackStatus bits.
     *
     *
     * <b>Optional parameters:</b> depending on corresponding [@a options
     * bits] additional parameters may follow @a status (in this order).
     *
     * @arg [@ref JackServerName] <em>(char *) server_name</em> selects
     * from among several possible concurrent server instances.  Server
     * names are unique to each user.  If unspecified, use "default"
     * unless \$JACK_DEFAULT_SERVER is defined in the process environment.
     *
     * @return Opaque client handle if successful.  If this is NULL, the
     * open operation failed, @a *status includes @ref JackFailure and the
     * caller is not a JACK client.
     */
    jack_client_t * jack_client_open (const char *client_name,
                                      jack_options_t options,
                                      jack_status_t *status, ...);

    /**
     * Attempt to become an external client of the Jack server.
     *
     * JACK is evolving a mechanism for automatically starting the server
     * when needed.  As a transition, jack_client_new() only does this
     * when \$JACK_START_SERVER is defined in the environment of the
     * calling process.  In the future this will become normal behavior.
     * For full control of this feature, use jack_client_open(), instead.
     * In either case, defining \$JACK_NO_START_SERVER disables this
     * feature.
     *
     * @param client_name of at most jack_client_name_size() characters.
     * If this name is already in use, the request fails.
     *
     * @return Opaque client handle if successful, otherwise NULL.
     *
     * @note Failure generally means that the JACK server is not running.
     * If there was some other problem, it will be reported via the @ref
     * jack_error_callback mechanism.  Use jack_client_open() and check
     * the @a status parameter for more detailed information.
     */
    jack_client_t * jack_client_new (const char *client_name);

    /**
     * Disconnects an external client from a JACK server.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_client_close (jack_client_t *client);

    /**
     * @return the maximum number of characters in a JACK client name
     * including the final NULL character.  This value is a constant.
     */
    int jack_client_name_size (void);

    /**
     * @return pointer to actual client name.  This is useful when @ref
     * JackUseExactName is not specified on open and @ref
     * JackNameNotUnique status was returned.  In that case, the actual
     * name will differ from the @a client_name requested.
     */
    char * jack_get_client_name (jack_client_t *client);

    /**
     * Load an internal client into the Jack server.
     *
     * Internal clients run inside the JACK server process.  They can use
     * most of the same functions as external clients.  Each internal
     * client must declare jack_initialize() and jack_finish() entry
     * points, called at load and unload times.  See inprocess.c for an
     * example of how to write an internal client.
     *
     * @deprecated Please use jack_internal_client_load().
     *
     * @param client_name of at most jack_client_name_size() characters.
     *
     * @param load_name of a shared object file containing the code for
     * the new client.
     *
     * @param load_init an arbitary string passed to the jack_initialize()
     * routine of the new client (may be NULL).
     *
     * @return 0 if successful.
     */
    int jack_internal_client_new (const char *client_name,
                                  const char *load_name,
                                  const char *load_init);

    jack_client_t* my_jack_internal_client_new(const char* client_name);

    /**
     * Remove an internal client from a JACK server.
     *
     * @deprecated Please use jack_internal_client_load().
     */
    void jack_internal_client_close (const char *client_name);

    void my_jack_internal_client_close (jack_client_t* client);

    /**
     * @param client pointer to JACK client structure.
     *
     * Check if the JACK subsystem is running with -R (--realtime).
     *
     * @return 1 if JACK is running realtime, 0 otherwise
     */
    int jack_is_realtime (jack_client_t *client);

    /**
     * @param client pointer to JACK client structure.
     * @param function The jack_shutdown function pointer.
     * @param 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().
     */
    void jack_on_shutdown (jack_client_t *client,
                           void (*function)(void *arg), void *arg);

    /**
     * Tell the Jack server to call @a process_callback whenever there is
     * work be done, passing @a 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.
     *
     * @return 0 on success, otherwise a non-zero error code, causing JACK
     * to remove that client from the process() graph.
     */
    int jack_set_process_callback (jack_client_t *client,
                                   JackProcessCallback process_callback,
                                   void *arg);

    /**
     * Tell JACK to call @a 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.
     *
     * @return 0 on success, otherwise a non-zero error code, causing JACK
     * to remove that client from the process() graph.
     */
    int jack_set_thread_init_callback (jack_client_t *client,
                                       JackThreadInitCallback thread_init_callback,
                                       void *arg);

    /**
     * Tell the Jack server to call @a freewheel_callback
     * whenever we enter or leave "freewheel" mode, passing @a
     * arg as the second argument. The first argument to the
     * callback will be non-zero if JACK is entering freewheel
     * mode, and zero otherwise.
     *
     * @return 0 on success, otherwise a non-zero error code.
     */
    int jack_set_freewheel_callback (jack_client_t *client,
                                     JackFreewheelCallback freewheel_callback,
                                     void *arg);

    /**
     * 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).
     * 
     * @param client pointer to JACK client structure
     * @param onoff  if non-zero, freewheel mode starts. Otherwise
     *                  freewheel mode ends.
     *
     * @return 0 on success, otherwise a non-zero error code.
     */
    int jack_set_freewheel(jack_client_t* client, int onoff);

    /**
     * Change the buffer size passed to the @a process_callback.
     *
     * This operation stops the JACK engine process cycle, then calls all
     * registered @a 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 jack_set_buffer_size_callback()
     *
     * @param client pointer to JACK client structure.
     * @param nframes new buffer size.  Must be a power of two.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_set_buffer_size (jack_client_t *client, jack_nframes_t nframes);

    /**
     * Tell JACK to call @a bufsize_callback whenever the size of the the
     * buffer that will be passed to the @a process_callback is about to
     * change.  Clients that depend on knowing the buffer size must supply
     * a @a bufsize_callback before activating themselves.
     *
     * @param client pointer to JACK client structure.
     * @param bufsize_callback function to call when the buffer size changes.
     * @param arg argument for @a bufsize_callback.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_set_buffer_size_callback (jack_client_t *client,
                                       JackBufferSizeCallback bufsize_callback,
                                       void *arg);

    /**
     * Tell the Jack server to call @a srate_callback whenever the system
     * sample rate changes.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_set_sample_rate_callback (jack_client_t *client,
                                       JackSampleRateCallback srate_callback,
                                       void *arg);

    /**
     * Tell the JACK server to call @a registration_callback whenever a
     * port is registered or unregistered, passing @a arg as a parameter.
     *
     * @return 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 @a graph_callback whenever the
     * processing graph is reordered, passing @a arg as a parameter.
     *
     * @return 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 @a xrun_callback whenever there is a
     * xrun, passing @a arg as a parameter.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_set_xrun_callback (jack_client_t *,
                                JackXRunCallback xrun_callback, void *arg);

    /**
     * Tell the Jack server that the program is ready to start processing
     * audio.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_activate (jack_client_t *client);

    /**
     * Tell the Jack server to remove this @a client from the process
     * graph.  Also, disconnect all ports belonging to it, since inactive
     * clients have no port connections.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_deactivate (jack_client_t *client);

    /**
     * Create a new port for the client. This is an object used for moving
     * data of any type in or out of the client.  Ports may be connected
     * in various ways.
     *
     * Each port has a short name.  The port's full name contains the name
     * of the client concatenated with a colon (:) followed by its short
     * name.  The jack_port_name_size() is the maximum length of this full
     * name.  Exceeding that will cause the port registration to fail and
     * return NULL.
     *
     * All ports have a type, which may be any non-NULL and non-zero
     * length string, passed as an argument.  Some port types are built
     * into the JACK API, currently only JACK_DEFAULT_AUDIO_TYPE.
     *
     * @param client pointer to JACK client structure.
     * @param port_name non-empty short name for the new port (not
     * including the leading @a "client_name:").
     * @param port_type port type name.  If longer than
     * jack_port_type_size(), only that many characters are significant.
     * @param flags @ref JackPortFlags bit mask.
     * @param buffer_size must be non-zero if this is not a built-in @a
     * port_type.  Otherwise, it is ignored.
     *
     * @return jack_port_t pointer on success, otherwise NULL.
     */
    jack_port_t * jack_port_register (jack_client_t *client,
                                      const char *port_name,
                                      const char *port_type,
                                      unsigned long flags,
                                      unsigned long buffer_size);

    /**
     * Remove the port from the client, disconnecting any existing
     * connections.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_unregister (jack_client_t *, jack_port_t *);

    /**
     * This returns a pointer to the memory area associated with the
     * specified port. For an output port, it will be a memory area
     * that can be written to; for an input port, it will be an area
     * containing the data from the port's connection(s), or
     * zero-filled. if there are multiple inbound connections, the data
     * will be mixed appropriately.  
     *
     * FOR OUTPUT PORTS ONLY
     * ---------------------
     * You may cache the value returned, but only between calls to
     * your "blocksize" callback. For this reason alone, you should
     * either never cache the return value or ensure you have
     * a "blocksize" callback and be sure to invalidate the cached
     * address from there.
     */
    void * jack_port_get_buffer (jack_port_t *, jack_nframes_t);

    /**
     * @return the full name of the jack_port_t (including the @a
     * "client_name:" prefix).
     *
     * @see jack_port_name_size().
     */
    const char * jack_port_name (const jack_port_t *port);

    /**
     * @return the short name of the jack_port_t (not including the @a
     * "client_name:" prefix).
     *
     * @see jack_port_name_size().
     */
    const char * jack_port_short_name (const jack_port_t *port);

    /**
     * @return the @ref JackPortFlags of the jack_port_t.
     */
    int jack_port_flags (const jack_port_t *port);

    /**
     * @return the @a port type, at most jack_port_type_size() characters
     * including a final NULL.
     */
    const char * jack_port_type (const jack_port_t *port);

    /**
     * @return TRUE if the jack_port_t belongs to the jack_client_t.
     */
    int jack_port_is_mine (const jack_client_t *, const jack_port_t *port);

    /**
     * @return number of connections to or from @a port.
     *
     * @pre The calling client must own @a port.
     */
    int jack_port_connected (const jack_port_t *port);

    /**
     * @return TRUE if the locally-owned @a port is @b directly connected
     * to the @a port_name.
     *
     * @see jack_port_name_size()
     */
    int jack_port_connected_to (const jack_port_t *port,
                                const char *port_name);

    /**
     * @return a null-terminated array of full port names to which the @a
     * port is connected.  If none, returns NULL.
     *
     * The caller is responsible for calling free(3) on any non-NULL
     * returned value.
     *
     * @param port locally owned jack_port_t pointer.
     *
     * @see jack_port_name_size(), jack_port_get_all_connections()
     */
    const char ** jack_port_get_connections (const jack_port_t *port);

    /**
     * @return a null-terminated array of full port names to which the @a
     * port is connected.  If none, returns NULL.
     *
     * The caller is responsible for calling free(3) on any non-NULL
     * returned value.
     *
     * This differs from jack_port_get_connections() in two important
     * respects:
     *
     *     1) You may not call this function from code that is
     *          executed in response to a JACK event. For example,
     *          you cannot use it in a GraphReordered handler.
     *
     *     2) You need not be the owner of the port to get information
     *          about its connections. 
     *
     * @see jack_port_name_size()
     */
    const char ** jack_port_get_all_connections (const jack_client_t *client,
            const jack_port_t *port);

    /**
     * A client may call this on a pair of its own ports to 
     * semi-permanently wire them together. This means that
     * a client that wants to direct-wire an input port to
     * an output port can call this and then no longer
     * have to worry about moving data between them. Any data
     * arriving at the input port will appear automatically
     * at the output port.
     *
     * The 'destination' port must be an output port. The 'source'
     * port must be an input port. Both ports must belong to
     * the same client. You cannot use this to tie ports between
     * clients. That is what a connection is for.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_tie (jack_port_t *src, jack_port_t *dst);

    /**
     * This undoes the effect of jack_port_tie(). The port
     * should be same as the 'destination' port passed to
     * jack_port_tie().
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_untie (jack_port_t *port);

    /**
     * A client may call this function to prevent other objects
     * from changing the connection status of a port. The port
     * must be owned by the calling client.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_lock (jack_client_t *, jack_port_t *);

    /**
     * This allows other objects to change the connection status of a port.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_unlock (jack_client_t *, jack_port_t *);

    /**
     * @return the time (in frames) between data being available or
     * delivered at/to a port, and the time at which it arrived at or is
     * delivered to the "other side" of the port.  E.g. for a physical
     * audio output port, this is the time between writing to the port and
     * when the signal will leave the connector.  For a physical audio
     * input port, this is the time between the sound arriving at the
     * connector and the corresponding frames being readable from the
     * port.
     */
    jack_nframes_t jack_port_get_latency (jack_port_t *port);

    /**
     * The maximum of the sum of the latencies in every
     * connection path that can be drawn between the port and other
     * ports with the @ref JackPortIsTerminal flag set.
     */
    jack_nframes_t jack_port_get_total_latency (jack_client_t *,
            jack_port_t *port);

    /**
     * The port latency is zero by default. Clients that control
     * physical hardware with non-zero latency should call this
     * to set the latency to its correct value. Note that the value
     * should include any systemic latency present "outside" the
     * physical hardware controlled by the client. For example,
     * for a client controlling a digital audio interface connected
     * to an external digital converter, the latency setting should
     * include both buffering by the audio interface *and* the converter. 
     */
    void jack_port_set_latency (jack_port_t *, jack_nframes_t);

    /**
     *
     */
    int jack_recompute_total_latencies (jack_client_t*);

    /**
     * Modify a port's short name.  May be called at any time.  If the
     * resulting full name (including the @a "client_name:" prefix) is
     * longer than jack_port_name_size(), it will be truncated.
     *
     * @return 0 on success, otherwise a non-zero error code.
     */
    int jack_port_set_name (jack_port_t *port, const char *port_name);

    /**
     * If @ref JackPortCanMonitor is set for this @a port, turn input
     * monitoring on or off.  Otherwise, do nothing.
     */
    int jack_port_request_monitor (jack_port_t *port, int onoff);

    /**
     * If @ref JackPortCanMonitor is set for this @a port_name, turn input
     * monitoring on or off.  Otherwise, do nothing.
     *
     * @return 0 on success, otherwise a non-zero error code.
     *
     * @see jack_port_name_size()
     */
    int jack_port_request_monitor_by_name (jack_client_t *client,
                                           const char *port_name, int onoff);

    /**
     * If @ref JackPortCanMonitor is set for a port, this function turns
     * on input monitoring if it was off, and turns it off if only one
     * request has been made to turn it on.  Otherwise it does nothing.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_port_ensure_monitor (jack_port_t *port, int onoff);

    /**
     * @return TRUE if input monitoring has been requested for @a port.
     */
    int jack_port_monitoring_input (jack_port_t *port);

    /**
     * Establish a connection between two ports.
     *
     * When a connection exists, data written to the source port will
     * be available to be read at the destination port.
     *
     * @pre The port types must be identical.
     *
     * @pre The @ref JackPortFlags of the @a source_port must include @ref
     * JackPortIsOutput.
     *
     * @pre The @ref JackPortFlags of the @a destination_port must include
     * @ref JackPortIsInput.
     *
     * @return 0 on success, EEXIST if the connection is already made,
     * otherwise a non-zero error code
     */
    int jack_connect (jack_client_t *,
                      const char *source_port,
                      const char *destination_port);

    /**
     * Remove a connection between two ports.
     *
     * @pre The port types must be identical.
     *
     * @pre The @ref JackPortFlags of the @a source_port must include @ref
     * JackPortIsOutput.
     *
     * @pre The @ref JackPortFlags of the @a destination_port must include
     * @ref JackPortIsInput.
     *
     * @return 0 on success, otherwise a non-zero error code
     */
    int jack_disconnect (jack_client_t *,
                         const char *source_port,
                         const char *destination_port);

    /**
     * Perform the same function as jack_disconnect() using port handles
     * rather than names.  This avoids the name lookup inherent in the
     * name-based version.
     *
     * Clients connecting their own ports are likely to use this function,
     * while generic connection clients (e.g. patchbays) would use
     * jack_disconnect().
     */
    int jack_port_disconnect (jack_client_t *, jack_port_t *);

    /**
     * @return the maximum number of characters in a full JACK port name
     * including the final NULL character.  This value is a constant.
     *
     * A port's full name contains the owning client name concatenated
     * with a colon (:) followed by its short name and a NULL
     * character.
     */
    int jack_port_name_size(void);

    /**
     * @return the maximum number of characters in a JACK port type name
     * including the final NULL character.  This value is a constant.
     */
    int jack_port_type_size(void);

    /**
     * @return the sample rate of the jack system, as set by the user when
     * jackd was started.
     */
    jack_nframes_t jack_get_sample_rate (jack_client_t *);

    /**
     * @return the current maximum size that will ever be passed to the @a
     * 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 @a bufsize_callback so they will be notified if it
     * does.
     *
     * @see jack_set_buffer_size_callback()
     */
    jack_nframes_t jack_get_buffer_size (jack_client_t *);

    /**
     * @param port_name_pattern A regular expression used to select 
     * ports by name.  If NULL or of zero length, no selection based 
     * on name will be carried out.
     * @param type_name_pattern A regular expression used to select 
     * ports by type.  If NULL or of zero length, no selection based 
     * on type will be carried out.
     * @param flags A value used to select ports by their flags.  
     * If zero, no selection based on flags will be carried out.
     *
     * @return a NULL-terminated array of ports that match the specified
     * arguments.  The caller is responsible for calling free(3) any
     * non-NULL returned value.
     *
     * @see jack_port_name_size(), jack_port_type_size()
     */
    const char ** jack_get_ports (jack_client_t *,
                                  const char *port_name_pattern,
                                  const char *type_name_pattern,
                                  unsigned long flags);

    /**
     * @return address of the jack_port_t named @a port_name.
     *
     * @see jack_port_name_size()
     */
    jack_port_t * jack_port_by_name (jack_client_t *, const char *port_name);

    /**
     * @return address of the jack_port_t of a @a port_id.
     */
    jack_port_t * jack_port_by_id (jack_client_t *client,
                                   jack_port_id_t port_id);

    /**
     * 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().
     *
     * @return ENOSYS, function not implemented.
     */
    int jack_engine_takeover_timebase (jack_client_t *);

    /**
     * @return the time in frames that has passed since the JACK server
     * began the current process cycle.
     */
    jack_nframes_t jack_frames_since_cycle_start (const jack_client_t *);

    /**
     * @return an estimate of the current time in frames.  This is a
     * running counter, no significance should be attached to its value,
     * but it can be compared to a previously returned value.
     */
    jack_nframes_t jack_frame_time (const jack_client_t *);

    /**
     * @return the frame_time after the last processing of the graph
     * this is only to be used from the process callback. 
     *
     * This function can be used to put timestamps generated by 
     * jack_frame_time() in correlation to the current process cycle.
     */
    jack_nframes_t jack_last_frame_time (const jack_client_t *client);

    /**
     * @return 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.
     */
    float jack_cpu_load (jack_client_t *client);

    /**
     * @return the pthread ID of the thread running the JACK client side
     * code.
     */
    pthread_t jack_client_thread_id (jack_client_t *);

    /**
     * Display JACK error message.
     *
     * Set via jack_set_error_function(), otherwise a JACK-provided
     * default will print @a msg (plus a newline) to stderr.
     *
     * @param msg error message text (no newline at end).
     */
    extern void (*jack_error_callback)(const char *msg);

    /**
     * Set the @ref jack_error_callback for error message display.
     *
     * The JACK library provides two built-in callbacks for this purpose:
     * default_jack_error_callback() and silent_jack_error_callback().
     */
    void jack_set_error_function (void (*func)(const char *));

#ifdef __cplusplus
}
#endif

#endif /* __jack_h__ */