Class Bus

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.gobject.TypeInstance
org.gnome.gobject.GObject
org.gnome.gobject.InitiallyUnowned
org.freedesktop.gstreamer.gst.GstObject
org.freedesktop.gstreamer.gst.Bus
All Implemented Interfaces:
Proxy
@Generated("org.javagi.JavaGI") public class Bus extends GstObject

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 GMainLoop.

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.

  • Constructor Details

    • Bus

      public Bus(MemorySegment address)
      Create a Bus instance for the provided memory address.
      Parameters:
      address - the memory address of the native object

    • Bus

      public Bus()
      Create a new Bus.

  • Method Details

    • getType

      public static @Nullable Type getType()
      Get the GType of the Bus class.
      Returns:
      the GType

    • getMemoryLayout

      public static MemoryLayout getMemoryLayout()
      The memory layout of the native struct.
      Returns:
      the memory layout

    • asParent

      protected Bus asParent()
      Return this instance as if it were its parent type. Comparable to the Java super keyword, but ensures the parent typeclass is also used in native code.
      Overrides:
      asParent in class GstObject
      Returns:
      the instance as if it were its parent type

    • addSignalWatch

      public 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.

    • addSignalWatchFull

      public 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 GMainLoop 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.

      Parameters:
      priority - The priority of the watch.

    • addWatch

      public int addWatch(int priority, @Nullable BusFunc func)

      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.

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

      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 gst_bus_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 g_source_remove().

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

      Parameters:
      priority - The priority of the watch.
      func - A function to call when a message is received.
      Returns:
      The event source id or 0 if this Bus already got an event source.

    • asyncSignalFunc

      public boolean asyncSignalFunc(Message message, @Nullable MemorySegment data)
      A helper GstBusFunc that can be used to convert all asynchronous messages into signals.
      Parameters:
      message - the GstMessage received
      data - user data
      Returns:
      true

    • createWatch

      public @Nullable 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.

      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 GSource that can be added to a GMainLoop.

    • disableSyncMessageEmission

      public 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.

    • enableSyncMessageEmission

      public 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 GMainLoop.

    • getPollfd

      public void getPollfd(PollFD fd)

      Gets the file descriptor from the bus which can be used to get notified about messages being available with functions like g_poll(), and allows integration into other event loops based on file descriptors. Whenever a message is available, the POLLIN / IOCondition.IN event is set.

      Warning: NEVER read or write anything to the returned fd but only use it for getting notifications via g_poll() or similar and then use the normal GstBus API, e.g. gst_bus_pop().

      Parameters:
      fd - A GPollFD to fill
      Since:
      1.14

    • havePending

      public boolean havePending()
      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.

    • peek

      public @Nullable Message peek()
      Peeks the message on the top of the bus' queue. The message will remain on the bus' message queue.
      Returns:
      the GstMessage that is on the bus, or null if the bus is empty.

    • poll

      public @Nullable Message poll(Set<MessageType> events, ClockTime timeout)

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

      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 GMainLoop 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.

      Parameters:
      events - a mask of GstMessageType, representing the set of message types to poll for (note special handling of extended message types below)
      timeout - the poll timeout, as a GstClockTime, or GST_CLOCK_TIME_NONE to poll indefinitely.
      Returns:
      the message that was received, or null if the poll timed out.

    • poll

      public @Nullable Message poll(MessageType events, ClockTime timeout)

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

      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 GMainLoop 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.

      Parameters:
      events - a mask of GstMessageType, representing the set of message types to poll for (note special handling of extended message types below)
      timeout - the poll timeout, as a GstClockTime, or GST_CLOCK_TIME_NONE to poll indefinitely.
      Returns:
      the message that was received, or null if the poll timed out.

    • pop

      public @Nullable Message pop()
      Gets a message from the bus.
      Returns:
      the GstMessage that is on the bus, or null if the bus is empty.

    • popFiltered

      public @Nullable Message popFiltered(Set<MessageType> types)
      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.
      Parameters:
      types - message types to take into account
      Returns:
      the next GstMessage matching type that is on the bus, or null if the bus is empty or there is no message matching type.

    • popFiltered

      public @Nullable Message popFiltered(MessageType... types)
      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.
      Parameters:
      types - message types to take into account
      Returns:
      the next GstMessage matching type that is on the bus, or null if the bus is empty or there is no message matching type.

    • post

      public boolean post(Message message)
      Posts a message on the given bus. Ownership of the message is taken by the bus.
      Parameters:
      message - the GstMessage to post
      Returns:
      true if the message could be posted, false if the bus is flushing.

    • removeSignalWatch

      public void removeSignalWatch()
      Removes a signal watch previously added with gst_bus_add_signal_watch().

    • removeWatch

      public boolean removeWatch()
      Removes an installed bus watch from bus.
      Returns:
      true on success or false if this Bus has no event source.
      Since:
      1.6

    • setFlushing

      public void setFlushing(boolean flushing)
      If flushing, flushes out and unrefs 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.
      Parameters:
      flushing - whether or not to flush the bus

    • setSyncHandler

      public void setSyncHandler(@Nullable BusSyncHandler func)

      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 null was not thread-safe.

      Parameters:
      func - The handler function to install

    • syncSignalHandler

      public BusSyncReply syncSignalHandler(Message message, @Nullable MemorySegment data)
      A helper GstBusSyncHandler that can be used to convert all synchronous messages into signals.
      Parameters:
      message - the GstMessage received
      data - user data
      Returns:
      BusSyncReply.PASS

    • timedPop

      public @Nullable Message timedPop(ClockTime timeout)

      Gets 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.

      Parameters:
      timeout - a timeout
      Returns:
      the GstMessage that is on the bus after the specified timeout or null if the bus is empty after the timeout expired.

    • timedPopFiltered

      public @Nullable Message timedPopFiltered(ClockTime timeout, Set<MessageType> types)

      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 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.

      Parameters:
      timeout - a timeout in nanoseconds, or GST_CLOCK_TIME_NONE to wait forever
      types - message types to take into account, MessageType.ANY for any type
      Returns:
      a GstMessage matching the filter in types, or null if no matching message was found on the bus until the timeout expired.

    • timedPopFiltered

      public @Nullable Message timedPopFiltered(ClockTime timeout, MessageType... types)

      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 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.

      Parameters:
      timeout - a timeout in nanoseconds, or GST_CLOCK_TIME_NONE to wait forever
      types - message types to take into account, MessageType.ANY for any type
      Returns:
      a GstMessage matching the filter in types, or null if no matching message was found on the bus until the timeout expired.

    • message

      protected void message(Message message)
      A message has been posted on the bus.
      Parameters:
      message - the message that has been posted asynchronously

    • syncMessage

      protected void syncMessage(Message message)
      A message has been posted on the bus.
      Parameters:
      message - the message that has been posted synchronously

    • onMessage

      public SignalConnection<Bus.MessageCallback> onMessage(@Nullable String detail, Bus.MessageCallback handler)
      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 GMainLoop running.
      Parameters:
      detail - the signal detail
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitMessage

      public void emitMessage(@Nullable String detail, @Nullable Message message)
      Emits the "message" signal. See onMessage(String, Bus.MessageCallback).

    • onSyncMessage

      public SignalConnection<Bus.SyncMessageCallback> onSyncMessage(@Nullable String detail, Bus.SyncMessageCallback handler)

      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.

      Parameters:
      detail - the signal detail
      handler - the signal handler
      Returns:
      a signal handler ID to keep track of the signal connection
      See Also:

    • emitSyncMessage

      public void emitSyncMessage(@Nullable String detail, @Nullable Message message)
      Emits the "sync-message" signal. See onSyncMessage(String, Bus.SyncMessageCallback).

    • builder

      public static Bus.Builder<? extends Bus.Builder> builder()
      A Bus.Builder object constructs a Bus with the specified properties. Use the various set...() methods to set properties, and finish construction with Bus.Builder.build().
      Returns:
      the builder object