#[repr(transparent)]
pub struct Bus { /* private fields */ }
Expand description

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 glib::Source based notifications. This makes it possible to handle the delivery in the glib GMainLoop.

The glib::Source 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 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()][Self::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()][Self::add_watch_full()] or add_watch(). This function will install a glib::Source 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.

Implements

GstObjectExt, glib::ObjectExt

Implementations

Creates a new Bus instance.

Returns

a new Bus instance

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 [glib::MainContext::push_thread_default()][crate::glib::MainContext::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 remove_signal_watch() as many times as this function is called.

Instructs GStreamer to stop emitting the “sync-message” signal for this bus. See enable_sync_message_emission() for more information.

In the event that multiple pieces of code have called enable_sync_message_emission(), the sync-message emissions will only be stopped after all calls to 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.

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 disable_sync_message_emission() as many times as this function is called.

While this function looks similar to add_signal_watch(), it is not exactly the same – this function enables synchronous emission of signals when messages arrive; 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 GMainLoop.

Checks if there are pending messages on the bus that should be handled.

Returns

true if there are messages on the bus to be handled, false otherwise.

Peeks the message on the top of the bus’ queue. The message will remain on the bus’ message queue.

Returns

the Message that is on the bus, or None if the bus is empty.

Gets a message from the bus.

Returns

the Message that is on the bus, or None if the bus is empty.

Posts a message on the given bus. Ownership of the message is taken by the bus.

message

the Message to post

Returns

true if the message could be posted, false if the bus is flushing.

Removes a signal watch previously added with add_signal_watch().

Removes an installed bus watch from self.

Returns

true on success or false if self has no event source.

If flushing, flushes out and unrefs any messages queued in the bus. Releases references to the message origin objects. Will flush future messages until set_flushing() sets flushing to false.

flushing

whether or not to flush the bus

Gets a message from the bus, waiting up to the specified timeout.

If timeout is 0, this function behaves like pop(). If timeout is GST_CLOCK_TIME_NONE, this function will block forever until a message was posted on the bus.

timeout

a timeout

Returns

the Message that is on the bus after the specified timeout or None if the bus is empty after the timeout expired.

A message has been posted on the bus. This signal is emitted from a glib::Source added to the mainloop. this signal will only be emitted when there is a GMainLoop running.

message

the message that has been posted asynchronously

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 enable_sync_message_emission() before.

message

the message that has been posted synchronously

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 [glib::MainContext::push_thread_default()][crate::glib::MainContext::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 GMainLoop is running.

This function may be called multiple times. To clean up, the caller is responsible for calling 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.

priority

The priority of the watch.

Create watch for this bus. The glib::Source will be dispatched whenever a message is on the bus. After the GSource is dispatched, the message is popped off the bus and unreffed.

As with other watches, there can only be one watch on the bus, including any signal watch added with gst_bus_add_signal_watch.

Returns

a glib::Source that can be added to a GMainLoop.

Adds a bus 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 [glib::MainContext::push_thread_default()][crate::glib::MainContext::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.

The bus watch will only work if a GMainLoop is being run.

The watch can be removed using remove_watch() or by returning false from func. If the watch was added to the default main context it is also possible to remove the watch using [glib::Source::remove()][crate::glib::Source::remove()].

The bus watch will take its own reference to the self, so it is safe to unref self using gst_object_unref() after setting the bus watch.

func

A function to call when a message is received.

Returns

The event source id or 0 if self already got an event source.

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.

Before 1.16.3 it was not possible to replace an existing handler and clearing an existing handler with None was not thread-safe.

func

The handler function to install

notify

called when user_data becomes unused

Gets 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 pop_filtered(). If timeout is GST_CLOCK_TIME_NONE, this function will block forever until a matching message was posted on the bus.

timeout

a timeout in nanoseconds, or GST_CLOCK_TIME_NONE to wait forever

types

message types to take into account, GST_MESSAGE_ANY for any type

Returns

a Message matching the filter in types, or None if no matching message was found on the bus until the timeout expired.

Gets 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. It is not possible to use message enums beyond GST_MESSAGE_EXTENDED in the events mask.

types

message types to take into account

Returns

the next Message matching type_ that is on the bus, or None if the bus is empty or there is no message matching type_.

Trait Implementations

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