Bus

The GstBus is an object responsible for delivering GstMessage packets in a first-in first-out way from the streaming threads (see GstTask) to the application.

Since the application typically only wants to deal with delivery of these messages from one thread, the GstBus will marshall the messages between different threads. This is important since the actual streaming of media is done in another thread than the application.

The GstBus provides support for GSource based notifications. This makes it possible to handle the delivery in the glib mainloop.

The GSource callback function gst_bus_async_signal_func() can be used to convert all bus messages into signal emissions.

A message is posted on the bus with the gst_bus_post() method. With the gst_bus_peek() and gst_bus_pop() methods one can look at or retrieve a previously posted message.

The bus can be polled with the gst_bus_poll() method. This methods blocks up to the specified timeout value until one of the specified messages types is posted on the bus. The application can then gst_bus_pop() the messages from the bus to handle them. Alternatively the application can register an asynchronous bus function using gst_bus_add_watch_full() or gst_bus_add_watch(). This function will install a GSource in the default glib main loop and will deliver messages a short while after they have been posted. Note that the main loop should be running for the asynchronous callbacks.

It is also possible to get messages from the bus without any thread marshalling with the gst_bus_set_sync_handler() method. This makes it possible to react to a message in the same thread that posted the message on the bus. This should only be used if the application is able to deal with messages from different threads.

Every GstPipeline has one bus.

Note that a GstPipeline will set its bus into flushing state when changing from READY to NULL state.

Last reviewed on 2012-03-28 (0.11.3)

class Bus : ObjectGst {

protected

GstBus* gstBus;

GstBus* getBusStruct();

void* getStruct();

this(GstBus* gstBus);

void setStruct(GObject* obj);

uint addWatch(bool delegate(Message) dlg);

bool delegate(Message) onWatchListener;

static gboolean watchCallBack(GstBus* bus, GstMessage* msg, Bus bus_d);

void setSyncHandler(GstBusSyncReply delegate(Message) dlg);

GstBusSyncReply delegate(Message) onSyncHandlerListener;

static GstBusSyncReply syncHandlerCallBack(GstBus* bus, GstMessage* msg, Bus bus_d);

int[string] connectedSignals;

void delegate(Message, Bus)[] onMessageListeners;

void addOnMessage(void delegate(Message, Bus) dlg, ConnectFlags connectFlags);

static void callBackMessage(GstBus* busStruct, GstMessage* message, Bus _bus);

void delegate(Message, Bus)[] onSyncMessageListeners;

void addOnSyncMessage(void delegate(Message, Bus) dlg, ConnectFlags connectFlags);

static void callBackSyncMessage(GstBus* busStruct, GstMessage* message, Bus _bus);

this();

int post(Message message);

int havePending();

Message peek();

Message pop();

Message popFiltered(GstMessageType types);

Message timedPop(GstClockTime timeout);

Message timedPopFiltered(GstClockTime timeout, GstMessageType types);

void setFlushing(int flushing);

GstBusSyncReply syncSignalHandler(Message message, void* data);

Source createWatch();

uint addWatchFull(int priority, GstBusFunc func, void* userData, GDestroyNotify notify);

void disableSyncMessageEmission();

void enableSyncMessageEmission();

int asyncSignalFunc(Message message, void* data);

void addSignalWatch();

void addSignalWatchFull(int priority);

void removeSignalWatch();

Message poll(GstMessageType events, GstClockTime timeout);

}

Constructors

this this(GstBus* gstBus): Sets our main struct and passes it to the parent class
this this(): Creates a new GstBus instance.

Members

Functions

addOnMessage void addOnMessage(void delegate(Message, Bus) dlg, ConnectFlags connectFlags): A message has been posted on the bus. This signal is emitted from a GSource added to the mainloop. this signal will only be emitted when there is a mainloop running.
addOnSyncMessage void addOnSyncMessage(void delegate(Message, Bus) dlg, ConnectFlags connectFlags): A message has been posted on the bus. This signal is emitted from the thread that posted the message so one has to be careful with locking. This signal will not be emitted by default, you have to call gst_bus_enable_sync_message_emission() before. See Also GstMessage, GstElement
addSignalWatch void addSignalWatch(): Adds a bus signal watch to the default main context with the default priority (G_PRIORITY_DEFAULT). It is also possible to use a non-default main context set up using g_main_context_push_thread_default() (before one had to create a bus watch source and attach it to the desired main context 'manually'). After calling this statement, the bus will emit the "message" signal for each message posted on the bus. This function may be called multiple times. To clean up, the caller is responsible for calling gst_bus_remove_signal_watch() as many times as this function is called. MT safe.
addSignalWatchFull void addSignalWatchFull(int priority): Adds a bus signal watch to the default main context with the given priority (e.g. G_PRIORITY_DEFAULT). It is also possible to use a non-default main context set up using g_main_context_push_thread_default() (before one had to create a bus watch source and attach it to the desired main context 'manually'). After calling this statement, the bus will emit the "message" signal for each message posted on the bus when the main loop is running. This function may be called multiple times. To clean up, the caller is responsible for calling gst_bus_remove_signal_watch() as many times as this function is called. There can only be a single bus watch per bus, you must remove any signal watch before you can set another type of watch. MT safe.
addWatch uint addWatch(bool delegate(Message) dlg): Adds a bus watch to the default main context with the default priority. This function is used to receive asynchronous messages in the main loop. The watch can be removed using g_source_remove() or by returning FALSE from func. MT safe.
addWatchFull uint addWatchFull(int priority, GstBusFunc func, void* userData, GDestroyNotify notify): Adds a bus watch to the default main context with the given priority (e.g. G_PRIORITY_DEFAULT). It is also possible to use a non-default main context set up using g_main_context_push_thread_default() (before one had to create a bus watch source and attach it to the desired main context 'manually'). This function is used to receive asynchronous messages in the main loop. There can only be a single bus watch per bus, you must remove it before you can set a new one. When func is called, the message belongs to the caller; if you want to keep a copy of it, call gst_message_ref() before leaving func. The watch can be removed using g_source_remove() or by returning FALSE from func. MT safe.
asyncSignalFunc int asyncSignalFunc(Message message, void* data): A helper GstBusFunc that can be used to convert all asynchronous messages into signals.
createWatch Source createWatch(): Create watch for this bus. The GSource will be dispatched whenever a message is on the bus. After the GSource is dispatched, the message is popped off the bus and unreffed.
disableSyncMessageEmission void disableSyncMessageEmission(): Instructs GStreamer to stop emitting the "sync-message" signal for this bus. See gst_bus_enable_sync_message_emission() for more information. In the event that multiple pieces of code have called gst_bus_enable_sync_message_emission(), the sync-message emissions will only be stopped after all calls to gst_bus_enable_sync_message_emission() were "cancelled" by calling this function. In this way the semantics are exactly the same as gst_object_ref() that which calls enable should also call disable. MT safe.
enableSyncMessageEmission void enableSyncMessageEmission(): Instructs GStreamer to emit the "sync-message" signal after running the bus's sync handler. This function is here so that code can ensure that they can synchronously receive messages without having to affect what the bin's sync handler is. This function may be called multiple times. To clean up, the caller is responsible for calling gst_bus_disable_sync_message_emission() as many times as this function is called. While this function looks similar to gst_bus_add_signal_watch(), it is not exactly the same -- this function enables synchronous emission of signals when messages arrive; gst_bus_add_signal_watch() adds an idle callback to pop messages off the bus asynchronously. The sync-message signal comes from the thread of whatever object posted the message; the "message" signal is marshalled to the main thread via the main loop. MT safe.
getBusStruct GstBus* getBusStruct(): Get the main Gtk struct
getStruct void* getStruct(): the main Gtk struct as a void*
havePending int havePending(): Check if there are pending messages on the bus that should be handled.
peek Message peek(): Peek the message on the top of the bus' queue. The message will remain on the bus' message queue. A reference is returned, and needs to be unreffed by the caller.
poll Message poll(GstMessageType events, GstClockTime timeout): Poll the bus for messages. Will block while waiting for messages to come. You can specify a maximum time to poll with the timeout parameter. If timeout is negative, this function will block indefinitely. All messages not in events will be popped off the bus and will be ignored. Because poll is implemented using the "message" signal enabled by gst_bus_add_signal_watch(), calling gst_bus_poll() will cause the "message" signal to be emitted for every message that poll sees. Thus a "message" signal handler will see the same messages that this function sees -- neither will steal messages from the other. This function will run a main loop from the default main context when polling. You should never use this function, since it is pure evil. This is especially true for GUI applications based on Gtk+ or Qt, but also for any other non-trivial application that uses the GLib main loop. As this function runs a GLib main loop, any callback attached to the default GLib main context may be invoked. This could be timeouts, GUI events, I/O events etc.; even if gst_bus_poll() is called with a 0 timeout. Any of these callbacks may do things you do not expect, e.g. destroy the main application window or some other resource; change other application state; display a dialog and run another main loop until the user clicks it away. In short, using this function may add a lot of complexity to your code through unexpected re-entrancy and unexpected changes to your application's state. For 0 timeouts use gst_bus_pop_filtered() instead of this function; for other short timeouts use gst_bus_timed_pop_filtered(); everything else is better handled by setting up an asynchronous bus watch and doing things from there.
pop Message pop(): Get a message from the bus.
popFiltered Message popFiltered(GstMessageType types): Get a message matching type from the bus. Will discard all messages on the bus that do not match type and that have been posted before the first message that does match type. If there is no message matching type on the bus, all messages will be discarded.
post int post(Message message): Post a message on the given bus. Ownership of the message is taken by the bus.
removeSignalWatch void removeSignalWatch(): Removes a signal watch previously added with gst_bus_add_signal_watch(). MT safe.
setFlushing void setFlushing(int flushing): If flushing, flush out and unref any messages queued in the bus. Releases references to the message origin objects. Will flush future messages until gst_bus_set_flushing() sets flushing to FALSE. MT safe.
setStruct void setStruct(GObject* obj): Undocumented in source. Be warned that the author may not have intended to support it.
setSyncHandler void setSyncHandler(GstBusSyncReply delegate(Message) dlg): Use this for making an XOverlay. Sets the synchronous handler on the bus. The function will be called every time a new message is posted on the bus. Note that the function will be called in the same thread context as the posting object. This function is usually only called by the creator of the bus. Applications should handle messages asynchronously using the gst_bus watch and poll functions. You cannot replace an existing sync_handler. You can pass NULL to this function, which will clear the existing handler.
syncSignalHandler GstBusSyncReply syncSignalHandler(Message message, void* data): A helper GstBusSyncHandler that can be used to convert all synchronous messages into signals.
timedPop Message timedPop(GstClockTime timeout): Get a message from the bus, waiting up to the specified timeout. If timeout is 0, this function behaves like gst_bus_pop(). If timeout is GST_CLOCK_TIME_NONE, this function will block forever until a message was posted on the bus.
timedPopFiltered Message timedPopFiltered(GstClockTime timeout, GstMessageType types): Get a message from the bus whose type matches the message type mask types, waiting up to the specified timeout (and discarding any messages that do not match the mask provided). If timeout is 0, this function behaves like gst_bus_pop_filtered(). If timeout is GST_CLOCK_TIME_NONE, this function will block forever until a matching message was posted on the bus.

Static functions

callBackMessage void callBackMessage(GstBus* busStruct, GstMessage* message, Bus _bus): Undocumented in source. Be warned that the author may not have intended to support it.
callBackSyncMessage void callBackSyncMessage(GstBus* busStruct, GstMessage* message, Bus _bus): Undocumented in source. Be warned that the author may not have intended to support it.
syncHandlerCallBack GstBusSyncReply syncHandlerCallBack(GstBus* bus, GstMessage* msg, Bus bus_d): Undocumented in source. Be warned that the author may not have intended to support it.
watchCallBack gboolean watchCallBack(GstBus* bus, GstMessage* msg, Bus bus_d): Undocumented in source. Be warned that the author may not have intended to support it.

Variables

connectedSignals int[string] connectedSignals;
gstBus GstBus* gstBus;: the main Gtk struct
onMessageListeners void delegate(Message, Bus)[] onMessageListeners;: Undocumented in source.
onSyncHandlerListener GstBusSyncReply delegate(Message) onSyncHandlerListener;: Undocumented in source.
onSyncMessageListeners void delegate(Message, Bus)[] onSyncMessageListeners;: Undocumented in source.
onWatchListener bool delegate(Message) onWatchListener;: Undocumented in source.

Inherited Members

From ObjectGst

gstObject GstObject* gstObject;: the main Gtk struct
getObjectGstStruct GstObject* getObjectGstStruct(): Get the main Gtk struct
getStruct void* getStruct(): the main Gtk struct as a void*
setStruct void setStruct(GObject* obj): Undocumented in source. Be warned that the author may not have intended to support it.
connectedSignals int[string] connectedSignals;
onDeepNotifyListeners void delegate(ObjectGst, ParamSpec, ObjectGst)[] onDeepNotifyListeners;: Undocumented in source.
addOnDeepNotify void addOnDeepNotify(void delegate(ObjectGst, ParamSpec, ObjectGst) dlg, ConnectFlags connectFlags): The deep notify signal is used to be notified of property changes. It is typically attached to the toplevel bin to receive notifications from all the elements contained in that bin.
callBackDeepNotify void callBackDeepNotify(GstObject* gstobjectStruct, GstObject* propObject, GParamSpec* prop, ObjectGst _objectGst): Undocumented in source. Be warned that the author may not have intended to support it.
setName int setName(string name): Sets the name of object, or gives object a guaranteed unique name (if name is NULL). This function makes a copy of the provided name, so the caller retains ownership of the name it sent.
getName string getName(): Returns a copy of the name of object. Caller should g_free() the return value after usage. For a nameless object, this returns NULL, which you can safely g_free() as well. Free-function: g_free
setParent int setParent(ObjectGst parent): Sets the parent of object to parent. The object's reference count will be incremented, and any floating reference will be removed (see gst_object_ref_sink()).
getParent ObjectGst getParent(): Returns the parent of object. This function increases the refcount of the parent object so you should gst_object_unref() it after usage.
unparent void unparent(): Clear the parent of object, removing the associated reference. This function decreases the refcount of object. MT safe. Grabs and releases object's lock.
defaultDeepNotify void defaultDeepNotify(ObjectG object, ObjectGst orig, ParamSpec pspec, string[] excludedProps): A default deep_notify signal callback for an object. The user data should contain a pointer to an array of strings that should be excluded from the notify. The default handler will print the new value of the property using g_print. MT safe. This function grabs and releases object's LOCK for getting its path string.
defaultError void defaultError(ErrorG error, char dbug): A default error function that uses g_printerr() to display the error message and the optional debug sting.. The default handler will simply print the error string using g_print.
checkUniqueness int checkUniqueness(ListG list, string name): Checks to see if there is any object named name in list. This function does not do any locking of any kind. You might want to protect the provided list with the lock of the owner of the list. This function will lock each GstObject in the list to compare the name, so be carefull when passing a list with a locked object.
hasAncestor int hasAncestor(ObjectGst ancestor): Check if object has an ancestor ancestor somewhere up in the hierarchy. One can e.g. check if a GstElement is inside a GstPipeline.
doref void* doref(void* object): Increments the reference count on object. This function does not take the lock on object because it relies on atomic refcounting. This object returns the input parameter to ease writing
unref void unref(void* object): Decrements the reference count on object. If reference count hits zero, destroy object. This function does not take the lock on object as it relies on atomic refcounting. The unref method should never be called with the LOCK held since this might deadlock the dispose function.
refSink void* refSink(void* object): Increase the reference count of object, and possibly remove the floating reference, if object has a floating reference. In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.
replace int replace(ObjectGst oldobj, ObjectGst newobj): Atomically modifies a pointer to point to a new object. The reference count of oldobj is decreased and the reference count of newobj is increased. Either newobj and the value pointed to by oldobj may be NULL.
getPathString string getPathString(): Generates a string describing the path of object in the object hierarchy. Only useful (or used) for debugging. Free-function: g_free
suggestNextSync GstClockTime suggestNextSync(): Returns a suggestion for timestamps where buffers should be split to get best controller results.
syncValues int syncValues(GstClockTime timestamp): Sets the properties of the object, according to the GstControlSources that (maybe) handle them and for the given timestamp. If this function fails, it is most likely the application developers fault. Most probably the control sources are not setup correctly.
hasActiveControlBindings int hasActiveControlBindings(): Check if the object has an active controlled properties.
setControlBindingsDisabled void setControlBindingsDisabled(int disabled): This function is used to disable all controlled properties of the object for some time, i.e. gst_object_sync_values() will do nothing.
setControlBindingDisabled void setControlBindingDisabled(string propertyName, int disabled): This function is used to disable the GstController on a property for some time, i.e. gst_controller_sync_values() will do nothing for the property.
addControlBinding int addControlBinding(ControlBinding binding): Attach the GstControlBinding to the object. If there already was a GstControlBinding for this property it will be replaced. The object will take ownership of the binding.
getControlBinding ControlBinding getControlBinding(string propertyName): Gets the corresponding GstControlBinding for the property. This should be unreferenced again after use.
removeControlBinding int removeControlBinding(ControlBinding binding): Removes the corresponding GstControlBinding. If it was the last ref of the binding, it will be disposed.
getValue Value getValue(string propertyName, GstClockTime timestamp): Gets the value for the given controlled property at the requested time.
getValueArray int getValueArray(string propertyName, GstClockTime timestamp, GstClockTime interval, void[] values): Gets a number of values for the given controlled property starting at the requested time. The array values need to hold enough space for n_values of the same type as the objects property's type. This function is useful if one wants to e.g. draw a graph of the control curve or apply a control curve sample by sample. The values are unboxed and ready to be used. The similar function gst_object_get_g_value_array() returns the array as GValues and is better suites for bindings.
getGValueArray int getGValueArray(string propertyName, GstClockTime timestamp, GstClockTime interval, uint nValues, Value values): Gets a number of GValues for the given controlled property starting at the requested time. The array values need to hold enough space for n_values of GValue. This function is useful if one wants to e.g. draw a graph of the control curve or apply a control curve sample by sample.
getControlRate GstClockTime getControlRate(): Obtain the control-rate for this object. Audio processing GstElement objects will use this rate to sub-divide their processing loop and call gst_object_sync_values() inbetween. The length of the processing segment should be up to control-rate nanoseconds. If the object is not under property control, this will return GST_CLOCK_TIME_NONE. This allows the element to avoid the sub-dividing. The control-rate is not expected to change if the element is in GST_STATE_PAUSED or GST_STATE_PLAYING.
setControlRate void setControlRate(GstClockTime controlRate): Change the control-rate for this object. Audio processing GstElement objects will use this rate to sub-divide their processing loop and call gst_object_sync_values() inbetween. The length of the processing segment should be up to control-rate nanoseconds. The control-rate should not change if the element is in GST_STATE_PAUSED or GST_STATE_PLAYING.