public 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 EXTENDED in the events mask

Because poll is implemented using the "message" signal enabled by gst_bus_add_signal_watch, calling 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 MainLoop 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 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 pop_filtered instead of this function; for other short timeouts use timed_pop_filtered; everything else is better handled by setting up an asynchronous bus watch and doing things from there.



a Bus


a mask of MessageType, representing the set of message types to poll for (note special handling of extended message types below)


the poll timeout, as a ClockTime, or CLOCK_TIME_NONE to poll indefinitely.


the message that was received, or null if the poll timed out.