maximum priority source to check
location to store timeout to be used in polling
location to store gstreamer.PollFD records that need to be polled.
the number of records actually stored in fds, or, if more than n_fds records need to be stored, the number of records that need to be stored.
Determines information necessary to poll this main loop.
You must have successfully acquired the context with MainContext.acquire before you may call this function.