text: /*
    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.
  
  */
  
  #ifndef __jack_h__
  #define __jack_h__
  
  #ifdef __cplusplus
  extern "C"
  {
  #endif
  
  #include <jack/systemdeps.h>
  #include <jack/types.h>
  #include <jack/transport.h>
  
  /**
   * Note: More documentation can be found in jack/types.h.
   */
  
      /*************************************************************
       * NOTE: JACK_WEAK_EXPORT ***MUST*** be used on every function
       * added to the JACK API after the 0.116.2 release.
       *
       * Functions that predate this release are marked with
       * JACK_WEAK_OPTIONAL_EXPORT which can be defined at compile
       * time in a variety of ways. The default definition is empty,
       * so that these symbols get normal linkage. If you wish to
       * use all JACK symbols with weak linkage, include
       * <jack/weakjack.h> before jack.h.
       *************************************************************/
  
  #include <jack/weakmacros.h>
  
  /**
   * Call this function to get version of the JACK, in form of several numbers
   *
   * @param major_ptr pointer to variable receiving major version of JACK.
   *
   * @param minor_ptr pointer to variable receiving minor version of JACK.
   *
   * @param major_ptr pointer to variable receiving micro version of JACK.
   *
   * @param major_ptr pointer to variable receiving protocol version of JACK.
   *
   */
  void
  jack_get_version(
      int *major_ptr,
      int *minor_ptr,
      int *micro_ptr,
      int *proto_ptr) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Call this function to get version of the JACK, in form of a string
   *
   * @return Human readable string describing JACK version being used.
   *
   */
  const char *
  jack_get_version_string(void) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @defgroup ClientFunctions Creating & manipulating clients
   * @{
   */
  
  /**
   * 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, ...) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
  * \bold THIS FUNCTION IS DEPRECATED AND SHOULD NOT BE USED IN
  *  NEW JACK CLIENTS
  *
  * @deprecated Please use jack_client_open().
  */
  jack_client_t * jack_client_new (const char *client_name) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Get the session ID for a client name.
   *
   * The session manager needs this to reassociate a client name to the session_id.
   *
   * The caller is responsible for calling jack_free(3) on any non-NULL
   * returned value.
   */
  char *jack_get_uuid_for_client_name (jack_client_t *client,
                                       const char    *client_name) JACK_WEAK_EXPORT;
  
  /**
   * Get the client name for a session_id.
   *
   * In order to snapshot the graph connections, the session manager needs to map
   * session_ids to client names.
   *
   * The caller is responsible for calling jack_free(3) on any non-NULL
   * returned value.
   */
  char *jack_get_client_name_by_uuid (jack_client_t *client,
                                      const char    *client_uuid ) JACK_WEAK_EXPORT;
  
  /**
   * 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 arbitrary 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_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * Remove an internal client from a JACK server.
   *
   * @deprecated Please use jack_internal_client_unload().
   */
  void jack_internal_client_close (const char *client_name) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return pid of client. If not available, 0 will be returned.
   */
  int jack_get_client_pid (const char *name) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the pthread ID of the thread running the JACK client side
   * real-time code.
   */
  jack_native_thread_t jack_client_thread_id (jack_client_t *client) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @defgroup NonCallbackAPI The non-callback API
   * @{
   */
  
  /**
   * \bold THIS FUNCTION IS DEPRECATED AND SHOULD NOT BE USED IN
   *  NEW JACK CLIENTS.
   *
   * @deprecated Please use jack_cycle_wait() and jack_cycle_signal() functions.
   */
  jack_nframes_t jack_thread_wait (jack_client_t *client, int status) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Wait until this JACK client should process data.
   *
   * @param client - pointer to a JACK client structure
   *
   * @return the number of frames of data to process
   */
  jack_nframes_t jack_cycle_wait (jack_client_t* client) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Signal next clients in the graph.
   *
   * @param client - pointer to a JACK client structure
   * @param status - if non-zero, calling thread should exit
   */
  void jack_cycle_signal (jack_client_t* client, int status) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Tell the Jack server to call @a thread_callback in the RT thread.
   * Typical use are in conjunction with @a jack_cycle_wait and @a jack_cycle_signal functions.
   * 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.
   *
   * 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_process_thread(jack_client_t* client, JackThreadCallback thread_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup ClientCallbacks Setting Client Callbacks
   * @{
   */
  
  /**
   * 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.
   *
   * 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, 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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().
   *
   * NOTE: if a client calls this AND jack_on_info_shutdown(), then
   * in case of a client thread shutdown, the callback
   * passed to this function will not be called, and the one passed to
   * jack_on_info_shutdown() will.
   *
   * NOTE: application should typically signal another thread to correctly 
   * finish cleanup, that is by calling "jack_client_close" 
   * (since "jack_client_close" cannot be called directly in the context 
   * of the thread that calls the shutdown callback).
   */
  void jack_on_shutdown (jack_client_t *client,
                         JackShutdownCallback shutdown_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @param client pointer to JACK client structure.
   * @param function The jack_info_shutdown function pointer.
   * @param arg The arguments for the jack_info_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().
   *
   * NOTE: if a client calls this AND jack_on_shutdown(), then
   * in case of a client thread shutdown, the callback passed to
   * jack_on_info_shutdown() will be called.
   *
   * NOTE: application should typically signal another thread to correctly 
   * finish cleanup, that is by calling "jack_client_close" 
   * (since "jack_client_close" cannot be called directly in the context 
   * of the thread that calls the shutdown callback).
   */
  void jack_on_info_shutdown (jack_client_t *client,
                              JackInfoShutdownCallback shutdown_callback, void *arg) JACK_WEAK_EXPORT;
  
  /**
   * 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.
   *
   * 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_process_callback (jack_client_t *client,
                                 JackProcessCallback process_callback,
                                 void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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.
   *
   * All "notification events" are received in a separated 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_freewheel_callback (jack_client_t *client,
                                   JackFreewheelCallback freewheel_callback,
                                   void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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.
   *
   * All "notification events" are received in a separated 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.)
   *
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Tell the Jack server to call @a srate_callback whenever the system
   * sample rate changes.
   *
   * All "notification events" are received in a separated 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_sample_rate_callback (jack_client_t *client,
                                     JackSampleRateCallback srate_callback,
                                     void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Tell the JACK server to call @a client_registration_callback whenever a
   * client is registered or unregistered, passing @a arg as a parameter.
   *
   * All "notification events" are received in a separated 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_client_registration_callback (jack_client_t *client,
                                              JackClientRegistrationCallback
                                              registration_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Tell the JACK server to call @a registration_callback whenever a
   * port is registered or unregistered, passing @a arg as a parameter.
   *
   * All "notification events" are received in a separated 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_port_registration_callback (jack_client_t *client,
                                            JackPortRegistrationCallback
                                            registration_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
   /**
   * Tell the JACK server to call @a connect_callback whenever a
   * port is connected or disconnected, passing @a arg as a parameter.
   *
   * All "notification events" are received in a separated 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_port_connect_callback (jack_client_t *client,
                                      JackPortConnectCallback
                                      connect_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
   /**
   * Tell the JACK server to call @a rename_callback whenever a
   * port is renamed, passing @a arg as a parameter.
   *
   * All "notification events" are received in a separated 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_port_rename_callback (jack_client_t *client,
                                     JackPortRenameCallback
                                     rename_callback, void *arg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Tell the JACK server to call @a graph_callback whenever the
   * processing graph is reordered, passing @a arg as a parameter.
   *
   * All "notification events" are received in a separated 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_graph_order_callback (jack_client_t *client,
                                     JackGraphOrderCallback graph_callback,
                                     void *) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 separated 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;
  
  /*@}*/
  
  /**
   * Tell the Jack server to call @a latency_callback whenever it
   * is necessary to recompute the latencies for some or all
   * Jack ports.
   *
   * @a latency_callback will be called twice each time it is
   * needed, once being passed JackCaptureLatency and once
   * JackPlaybackLatency. See @ref LatencyFunctions for
   * the definition of each type of latency and related functions.
   *
   * <b>IMPORTANT: Most JACK clients do NOT need to register a latency
   * callback.</b>
   *
   * Clients that meet any of the following conditions do NOT
   * need to register a latency callback:
   *
   *    - have only input ports
   *    - have only output ports
   *    - their output is totally unrelated to their input
   *    - their output is not delayed relative to their input
   *        (i.e. data that arrives in a given process()
   *         callback is processed and output again in the
   *         same callback)
   *
   * Clients NOT registering a latency callback MUST also
   * satisfy this condition:
   *
   *    - have no multiple distinct internal signal pathways
   *
   * This means that if your client has more than 1 input and
   * output port, and considers them always "correlated"
   * (e.g. as a stereo pair), then there is only 1 (e.g. stereo)
   * signal pathway through the client. This would be true,
   * for example, of a stereo FX rack client that has a
   * left/right input pair and a left/right output pair.
   *
   * However, this is somewhat a matter of perspective. The
   * same FX rack client could be connected so that its
   * two input ports were connected to entirely separate
   * sources. Under these conditions, the fact that the client
   * does not register a latency callback MAY result
   * in port latency values being incorrect.
   *
   * Clients that do not meet any of those conditions SHOULD
   * register a latency callback.
   *
   * Another case is when a client wants to use
   * @ref jack_port_get_latency_range(), which only returns meaninful
   * values when ports get connected and latency values change.
   *
   * See the documentation for  @ref jack_port_set_latency_range()
   * on how the callback should operate. Remember that the @a mode
   * argument given to the latency callback will need to be
   * passed into @ref jack_port_set_latency_range()
   *
   * @return 0 on success, otherwise a non-zero error code
   */
  int jack_set_latency_callback (jack_client_t *client,
  			       JackLatencyCallback latency_callback,
  			       void *) JACK_WEAK_EXPORT;
  /*@}*/
  
  /**
   * @defgroup ServerClientControl Controlling & querying JACK server operation
   * @{
   */
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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 *) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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 *) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 *) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup PortFunctions Creating & manipulating ports
   * @{
   */
  
  /**
   * 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.
   *
   * The @a port_name must be unique among all ports owned by this client.
   * If the name is not unique, the registration will fail.
   *
   * 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:"). Must be unique.
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 *client, jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 : DEPRECATED in Jack 2.0 !!
   * ---------------------------------------------------
   * 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.
   *
   * Caching output ports is DEPRECATED in Jack 2.0, due to some new optimization (like "pipelining").
   * Port buffers have to be retrieved in each callback for proper functioning.
   */
  void * jack_port_get_buffer (jack_port_t *port, jack_nframes_t) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the UUID of the jack_port_t
   *
   * @see jack_uuid_to_string() to convert into a string representation
   */
  jack_uuid_t jack_port_uuid (const jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the @ref JackPortFlags of the jack_port_t.
   */
  int jack_port_flags (const jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
   /**
   * @return the @a port type id.
   */
  jack_port_type_id_t jack_port_type_id (const jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return TRUE if the jack_port_t belongs to the jack_client_t.
   */
  int jack_port_is_mine (const jack_client_t *client, const jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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 jack_free() 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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 jack_free() 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   *
   * @deprecated This function will be removed from a future version
   * of JACK. Do not use it. There is no replacement. It has
   * turned out to serve essentially no purpose in real-life
   * JACK clients.
   */
  int jack_port_tie (jack_port_t *src, jack_port_t *dst) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   *
   * @deprecated This function will be removed from a future version
   * of JACK. Do not use it. There is no replacement. It has
   * turned out to serve essentially no purpose in real-life
   * JACK clients.
   */
  int jack_port_untie (jack_port_t *port) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * \bold THIS FUNCTION IS DEPRECATED AND SHOULD NOT BE USED IN
   *  NEW JACK CLIENTS
   *
   * 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) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * Modify a port's short name.  May NOT be called from a callback handling a server event.
   * 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.
   *
   * This differs from jack_port_set_name() by triggering PortRename notifications to
   * clients that have registered a port rename handler.
   */
  int jack_port_rename (jack_client_t* client, jack_port_t *port, const char *port_name) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Set @a alias as an alias for @a port.  May be called at any time.
   * If the alias is longer than jack_port_name_size(), it will be truncated.
   *
   * After a successful call, and until JACK exits or
   * @function jack_port_unset_alias() is called, @alias may be
   * used as a alternate name for the port.
   *
   * Ports can have up to two aliases - if both are already
   * set, this function will return an error.
   *
   * @return 0 on success, otherwise a non-zero error code.
   */
  int jack_port_set_alias (jack_port_t *port, const char *alias) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Remove @a alias as an alias for @a port.  May be called at any time.
   *
   * After a successful call, @a alias can no longer be
   * used as a alternate name for the port.
   *
   * @return 0 on success, otherwise a non-zero error code.
   */
  int jack_port_unset_alias (jack_port_t *port, const char *alias) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Get any aliases known for @port.
   *
   * @return the number of aliases discovered for the port
   */
  int jack_port_get_aliases (const jack_port_t *port, char* const aliases[2]) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return TRUE if input monitoring has been requested for @a port.
   */
  int jack_port_monitoring_input (jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 *client,
                    const char *source_port,
                    const char *destination_port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 *client,
                       const char *source_port,
                       const char *destination_port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * 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 *client, jack_port_t *port) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the buffersize of a port of type @arg port_type.
   *
   * this function may only be called in a buffer_size callback.
   */
  size_t jack_port_type_get_buffer_size (jack_client_t *client, const char *port_type) JACK_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup LatencyFunctions Managing and determining latency
   *
   * The purpose of JACK's latency API is to allow clients to
   * easily answer two questions:
   *
   * - How long has it been since the data read from a port arrived
   *   at the edge of the JACK graph (either via a physical port
   *   or being synthesized from scratch)?
   *
   * - How long will it be before the data written to a port arrives
   *   at the edge of a JACK graph?
  
   * To help answering these two questions, all JACK ports have two
   * latency values associated with them, both measured in frames:
   *
   * <b>capture latency</b>: how long since the data read from
   *                  the buffer of a port arrived at
   *                  a port marked with JackPortIsTerminal.
   *                  The data will have come from the "outside
   *                  world" if the terminal port is also
   *                  marked with JackPortIsPhysical, or
   *                  will have been synthesized by the client
   *                  that owns the terminal port.
   *
   * <b>playback latency</b>: how long until the data
   *                   written to the buffer of port will reach a port
   *                   marked with JackPortIsTerminal.
   *
   * Both latencies might potentially have more than one value
   * because there may be multiple pathways to/from a given port
   * and a terminal port. Latency is therefore generally
   * expressed a min/max pair.
   *
   * In most common setups, the minimum and maximum latency
   * are the same, but this design accommodates more complex
   * routing, and allows applications (and thus users) to
   * detect cases where routing is creating an anomalous
   * situation that may either need fixing or more
   * sophisticated handling by clients that care about
   * latency.
   *
   * See also @ref jack_set_latency_callback for details on how
   * clients that add latency to the signal path should interact
   * with JACK to ensure that the correct latency figures are
   * used.
   * @{
   */
  
  /**
   * 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.
   *
   * @deprecated This method will be removed in the next major
   * release of JACK. It should not be used in new code, and should
   * be replaced by a latency callback that calls @ref
   * jack_port_set_latency_range().
   */
  void jack_port_set_latency (jack_port_t *port, jack_nframes_t) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * return the latency range defined by @a mode for
   * @a port, in frames.
   *
   * See @ref LatencyFunctions for the definition of each latency value.
   *
   * This function is best used from callbacks, specifically the latency callback.
   * Before a port is connected, this returns the default latency: zero.
   * Therefore it only makes sense to call jack_port_get_latency_range() when
   * the port is connected, and that gets signalled by the latency callback.
   * See @ref jack_set_latency_callback() for details.
   */
  void jack_port_get_latency_range (jack_port_t *port, jack_latency_callback_mode_t mode, jack_latency_range_t *range) JACK_WEAK_EXPORT;
  
  /**
   * set the minimum and maximum latencies defined by
   * @a mode for @a port, in frames.
   *
   * See @ref LatencyFunctions for the definition of each latency value.
   *
   * This function should ONLY be used inside a latency
   * callback. The client should determine the current
   * value of the latency using @ref jack_port_get_latency_range()
   * (called using the same mode as @a mode)
   * and then add some number of frames to that reflects
   * latency added by the client.
   *
   * How much latency a client adds will vary
   * dramatically. For most clients, the answer is zero
   * and there is no reason for them to register a latency
   * callback and thus they should never call this
   * function.
   *
   * More complex clients that take an input signal,
   * transform it in some way and output the result but
   * not during the same process() callback will
   * generally know a single constant value to add
   * to the value returned by @ref jack_port_get_latency_range().
   *
   * Such clients would register a latency callback (see
   * @ref jack_set_latency_callback) and must know what input
   * ports feed which output ports as part of their
   * internal state. Their latency callback will update
   * the ports' latency values appropriately.
   *
   * A pseudo-code example will help. The @a mode argument to the latency
   * callback will determine whether playback or capture
   * latency is being set. The callback will use
   * @ref jack_port_set_latency_range() as follows:
   *
   * \code
   * jack_latency_range_t range;
   * if (mode == JackPlaybackLatency) {
   *  foreach input_port in (all self-registered port) {
   *   jack_port_get_latency_range (port_feeding_input_port, JackPlaybackLatency, &range);
   *   range.min += min_delay_added_as_signal_flows_from port_feeding to input_port;
   *   range.max += max_delay_added_as_signal_flows_from port_feeding to input_port;
   *   jack_port_set_latency_range (input_port, JackPlaybackLatency, &range);
   *  }
   * } else if (mode == JackCaptureLatency) {
   *  foreach output_port in (all self-registered port) {
   *   jack_port_get_latency_range (port_fed_by_output_port, JackCaptureLatency, &range);
   *   range.min += min_delay_added_as_signal_flows_from_output_port_to_fed_by_port;
   *   range.max += max_delay_added_as_signal_flows_from_output_port_to_fed_by_port;
   *   jack_port_set_latency_range (output_port, JackCaptureLatency, &range);
   *  }
   * }
   * \endcode
   *
   * In this relatively simple pseudo-code example, it is assumed that
   * each input port or output is connected to only 1 output or input
   * port respectively.
   *
   * If a port is connected to more than 1 other port, then the
   * range.min and range.max values passed to @ref
   * jack_port_set_latency_range() should reflect the minimum and
   * maximum values across all connected ports.
   *
   * See the description of @ref jack_set_latency_callback for more
   * information.
   */
  void jack_port_set_latency_range (jack_port_t *port, jack_latency_callback_mode_t mode, jack_latency_range_t *range) JACK_WEAK_EXPORT;
  
  /**
   * Request a complete recomputation of all port latencies. This
   * can be called by a client that has just changed the internal
   * latency of its port using  jack_port_set_latency
   * and wants to ensure that all signal pathways in the graph
   * are updated with respect to the values that will be returned
   * by  jack_port_get_total_latency. It allows a client
   * to change multiple port latencies without triggering a
   * recompute for each change.
   *
   * @return zero for successful execution of the request. non-zero
   *         otherwise.
   */
  int jack_recompute_total_latencies (jack_client_t *client) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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.
   *
   * @deprecated This method will be removed in the next major
   * release of JACK. It should not be used in new code, and should
   * be replaced by jack_port_get_latency_range() in any existing
   * use cases.
   */
  jack_nframes_t jack_port_get_latency (jack_port_t *port) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * 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.
   *
   * @deprecated This method will be removed in the next major
   * release of JACK. It should not be used in new code, and should
   * be replaced by jack_port_get_latency_range() in any existing
   * use cases.
   */
  jack_nframes_t jack_port_get_total_latency (jack_client_t *client,
  					    jack_port_t *port) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /**
   * Request a complete recomputation of a port's total latency. This
   * can be called by a client that has just changed the internal
   * latency of its port using  jack_port_set_latency
   * and wants to ensure that all signal pathways in the graph
   * are updated with respect to the values that will be returned
   * by  jack_port_get_total_latency.
   *
   * @return zero for successful execution of the request. non-zero
   *         otherwise.
   *
   * @deprecated This method will be removed in the next major
   * release of JACK. It should not be used in new code, and should
   * be replaced by jack_recompute_total_latencies() in any existing
   * use cases.
   */
  int jack_recompute_total_latency (jack_client_t*, jack_port_t* port) JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup PortSearching Looking up ports
   * @{
   */
  
  /**
   * @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 jack_free() any
   * non-NULL returned value.
   *
   * @see jack_port_name_size(), jack_port_type_size()
   */
  const char ** jack_get_ports (jack_client_t *client,
                                const char *port_name_pattern,
                                const char *type_name_pattern,
                                unsigned long flags) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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 *client, const char *port_name) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup TimeFunctions Handling time
   * @{
   *
   * JACK time is in units of 'frames', according to the current sample rate.
   * The absolute value of frame times is meaningless, frame times have meaning
   * only relative to each other.
   */
  
  /**
   * @return the estimated 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 *) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the estimated current time in frames.
   * This function is intended for use in other threads (not the process
   * callback).  The return value can be compared with the value of
   * jack_last_frame_time to relate time in other threads to JACK time.
   */
  jack_nframes_t jack_frame_time (const jack_client_t *) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the precise time at the start of the current process cycle.
   * This function may only be used from the process callback, and can
   * be used to interpret timestamps generated by jack_frame_time() in
   * other threads with respect to the current process cycle.
   *
   * This is the only jack time function that returns exact time:
   * when used during the process callback it always returns the same
   * value (until the next process callback, where it will return
   * that value + nframes, etc).  The return value is guaranteed to be
   * monotonic and linear in this fashion unless an xrun occurs.
   * If an xrun occurs, clients must check this value again, as time
   * may have advanced in a non-linear way (e.g. cycles may have been skipped).
   */
  jack_nframes_t jack_last_frame_time (const jack_client_t *client) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * This function may only be used from the process callback.
   * It provides the internal cycle timing information as used by
   * most of the other time related functions. This allows the
   * caller to map between frame counts and microseconds with full
   * precision (i.e. without rounding frame times to integers),
   * and also provides e.g. the microseconds time of the start of
   * the current cycle directly (it has to be computed otherwise).
   *
   * If the return value is zero, the following information is
   * provided in the variables pointed to by the arguments:
   *
   * current_frames: the frame time counter at the start of the
   *                 current cycle, same as jack_last_frame_time().
   * current_usecs:  the microseconds time at the start of the
   *                 current cycle.
   * next_usecs:     the microseconds time of the start of the next
   *                 next cycle as computed by the DLL.
   * period_usecs:   the current best estimate of the period time in
   *                  microseconds.
   *
   * NOTES:
   * 
   * Because of the types used, all the returned values except period_usecs
   * are unsigned. In computations mapping between frames and microseconds
   * *signed* differences are required. The easiest way is to compute those
   * separately and assign them to the appropriate signed variables,
   * int32_t for frames and int64_t for usecs. See the implementation of
   * jack_frames_to_time() and Jack_time_to_frames() for an example.
   * 
   * Unless there was an xrun, skipped cycles, or the current cycle is the
   * first after freewheeling or starting Jack, the value of current_usecs
   * will always be the value of next_usecs of the previous cycle.
   *
   * The value of period_usecs will in general NOT be exactly equal to
   * the difference of next_usecs and current_usecs. This is because to
   * ensure stability of the DLL and continuity of the mapping, a fraction
   * of the loop error must be included in next_usecs. For an accurate
   * mapping between frames and microseconds, the difference of next_usecs
   * and current_usecs should be used, and not period_usecs.
   *
   * @return zero if OK, non-zero otherwise.
   */
  int jack_get_cycle_times(const jack_client_t *client,
                          jack_nframes_t *current_frames,
                          jack_time_t    *current_usecs,
                          jack_time_t    *next_usecs,
                          float          *period_usecs) JACK_OPTIONAL_WEAK_EXPORT;
                    
  /**
   * @return the estimated time in microseconds of the specified frame time
   */
  jack_time_t jack_frames_to_time(const jack_client_t *client, jack_nframes_t) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return the estimated time in frames for the specified system time.
   */
  jack_nframes_t jack_time_to_frames(const jack_client_t *client, jack_time_t) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * @return return JACK's current system time in microseconds,
   *         using the JACK clock source.
   *
   * The value returned is guaranteed to be monotonic, but not linear.
   */
  jack_time_t jack_get_time(void) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * @defgroup ErrorOutput Controlling error/information output
   */
  /*@{*/
  
  /**
   * 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) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Set the @ref jack_error_callback for error message display.
   * Set it to NULL to restore default_jack_error_callback function.
   *
   * 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 *)) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Display JACK info message.
   *
   * Set via jack_set_info_function(), otherwise a JACK-provided
   * default will print @a msg (plus a newline) to stdout.
   *
   * @param msg info message text (no newline at end).
   */
  extern void (*jack_info_callback)(const char *msg) JACK_OPTIONAL_WEAK_EXPORT;
  
  /**
   * Set the @ref jack_info_callback for info message display.
   * Set it to NULL to restore default_jack_info_callback function.
   *
   * The JACK library provides two built-in callbacks for this purpose:
   * default_jack_info_callback() and silent_jack_info_callback().
   */
  void jack_set_info_function (void (*func)(const char *)) JACK_OPTIONAL_WEAK_EXPORT;
  
  /*@}*/
  
  /**
   * The free function to be used on memory returned by jack_port_get_connections,
   * jack_port_get_all_connections, jack_get_ports and jack_get_internal_client_name functions.
   * This is MANDATORY on Windows when otherwise all nasty runtime version related crashes can occur.
   * Developers are strongly encouraged to use this function instead of the standard "free" function in new code.
   *
   * @param ptr the memory pointer to be deallocated.
   */
  void jack_free(void* ptr) JACK_OPTIONAL_WEAK_EXPORT;
  
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* __jack_h__ */
  