Use private non-GLib-integrated D-Bus connection to fix main-loop CPU spin#33
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km1tch wants to merge 1 commit into
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Use private non-GLib-integrated D-Bus connection to fix main-loop CPU spin#33km1tch wants to merge 1 commit into
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… spin The shared dbus.SessionBus() singleton attaches its watch sources to the default GLib main context, because StreamController sets DBusGMainLoop(set_as_default=True) at startup. MediaController then makes blocking MPRIS calls (list_names, Properties.Get, ...) from the tick_actions thread. The blocking thread and the GTK main loop end up sharing one connection: the connection's GSource keeps reporting messages pending dispatch while the blocking thread owns the connection, so the main loop wakes, dispatches nothing, and immediately re-polls - forever. The result is one core pegged at 100% for the lifetime of the process. Confirmed with py-spy: the main thread is always inside g_main_context_iteration with no Python callback on the stack; a native profile shows ~43% of main-thread time in g_wakeup_signal eventfd writes and ~33% in ppoll. Fix: give MediaController a private connection with no main-loop integration (mainloop=dbus.mainloop.NULL_MAIN_LOOP). Blocking calls then poll their own socket, which is thread-safe and never touches the GLib context. This plugin registers no D-Bus signal receivers, so nothing here needs main-loop integration. Tested on a live deployment (GNOME Wayland, Python 3.14, dbus-python 1.4.0, GLib 2.88): main-thread CPU went from a sustained 99.9% to idle, and MPRIS control/metadata calls kept working against Firefox and MPD. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #32 — StreamController's GTK main thread spins at ~100% CPU whenever MediaPlugin is active.
What
One functional line:
MediaControllernow opens a private D-Bus connection with no main-loop integration (mainloop=dbus.mainloop.NULL_MAIN_LOOP) instead of the shareddbus.SessionBus()singleton.Why
StreamController core sets
DBusGMainLoop(set_as_default=True), so the shared session bus attaches its watch sources to the GTK main context. MediaController's MPRIS calls are all blocking calls from thetick_actionsthread, which leaves the connection's GSource permanently "ready" while the tick thread owns the connection — the main loop wakes, dispatches nothing, and re-polls forever, pegging one core for the lifetime of the process. Full analysis with py-spy native profiles in the linked issue.With a private non-integrated connection, blocking calls poll their own socket (thread-safe in libdbus) and never touch the GLib context.
Safety
connect_to_signal/add_signal_receiver), so nothing in this repo needs main-loop integration.private=Trueavoids mutating behavior of the shared singleton for core or other plugins.Tested
Live deployment on GNOME Wayland (Python 3.14, dbus-python 1.4.0, GLib 2.88): main-thread CPU drops from a sustained 99.9% to idle after this change; play/pause/next, metadata, album art, and player discovery verified working against Firefox and MPD.
Diagnosed and fixed with help from Claude (Fable 5) — attribution retained in the commit trailer.