mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-18 15:51:11 +00:00
84770e8437
Original commit message from CVS: * docs/design/part-events.txt: * docs/design/part-gstbus.txt: * docs/design/part-gstpipeline.txt: * docs/design/part-messages.txt: * docs/design/part-overview.txt: * docs/design/part-segments.txt: * gst/gstbin.c: * gst/gstbuffer.c: * gst/gstclock.c: * gst/gstelement.c: * gst/gstevent.c: * gst/gstfilter.c: * gst/gstiterator.c: Various documentation updates.
38 lines
1.8 KiB
Text
38 lines
1.8 KiB
Text
GstBus
|
|
------
|
|
|
|
The GstBus is an object responsible for delivering GstMessages in
|
|
a first-in first-out way from the streaming threads 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. Different GSources
|
|
can be added to the same bin provided they listen to different message types.
|
|
|
|
A message is posted on the bus with the gst_bus_post() method. With the
|
|
gst_bus_peek() and _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 _pop() the messages from the
|
|
bus to handle them.
|
|
|
|
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.
|
|
|
|
If no messages are popped from the bus with either a GSource or gst_bus_pop(),
|
|
they remain on the bus.
|
|
|
|
When a pipeline or bin goes from READY into NULL state, it will set its bus
|
|
to flushing, ie. the bus will drop all existing and new messages on the bus,
|
|
This is necessary because bus messages hold references to the bin/pipeline
|
|
or its elements, so there are circular references that need to be broken if
|
|
one ever wants to be able to destroy a bin or pipeline properly.
|