Callbacks could be queued to be invoked either on the impl side or the
main thread side of the thread; change this to take a GMainContext,
which effectively means a callback can be queued to be invoked on any
thread that has a GMainLoop running on its own GMainContext.
Flushing is made to handle flushing callbacks synchronously on all
threads. This works by keeping a hash table of queued callbacks per
thread (GMainContext); when flushing (from the main thread), callbacks
on the main thread context is flushed, followed by synchronization with
all the other threads.
meta_thread_flush_callbacks() is changed to no longer return the number
of dispatched callbacks; it becomes much harder when there are N queues
spread across multiple threads. Since it wasn't used for anything, just
drop the counting, making life slightly easier.
Feedback to thread tasks are however always queued on the callers
thread.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>
This isn't a problem for user space threads, as there are no race
conditions, but when kernel thread support is introduced, we must make
sure that e.g. the main loop is actually running before quitting it.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>
This uses the queue that was introduced when migrating impl task
management from MetaThread to MetaThreadImpl, with the exception that
it's now fully used as an actual queue. It now has a GSource that sits
on the right GMainContext that is dispatched whenever there are tasks to
execute.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>
It's the impl side that wants to add impl side idle sources, or fd
sources, etc, so make it part of MetaThreadImpl.
This changes things to be GAsyncQueue based. While things are still
technically single threaded, the GAsyncQueue type is used as later we'll
introduce queuing tasks asynchronously, then eventually queuing across
thread barriers.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2777>
