The Bus is an object responsible for delivering Message
packets in a first-in first-out way from the streaming threads (see Task) 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 SignalSource based notifications. This makes
it possible to handle the delivery in the glib mainloop.
The SignalSource callback function
async_signal_func can be used to convert all bus messages into
signal emissions.
A message is posted on the bus with the post method. With the
peek and pop
methods one can look at or retrieve a previously posted message.
The bus can be polled with the 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
pop the messages from the bus to handle them. Alternatively the application can
register an asynchronous bus function using add_watch_full or
gst_bus_add_watch. This function will install a SignalSource 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
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 Pipeline has one bus.
Note that a Pipeline will set its bus into flushing state when changing from
READY to NULL state.
Last reviewed on 2006-03-12 (0.10.5)
