GTK: audio bell leaks a GStreamer pipeline + GL-context threads per ring (idle CPU climbs over time)

[nikicat]

Issue Description

With bell-features = audio and an (optional) bell-audio-path set, every terminal bell leaks a GStreamer pipeline and its GL-context threads. They are never torn down, so over a long-running session CPU usage climbs steadily and thread count grows without bound.

After ~1.5 days of normal use (multiple long-lived TUI sessions that ring the bell on completion), a single Ghostty process had accumulated 3,482 threads and was consuming ~3 CPU cores while idle. Thread-name histogram from /proc/<pid>/task/*/comm:

1358 gldisplay-event
 696 ghostty:gdrv
 696 ghostt:traceq
 679 gstglcontext
  14 renderer / io / io-reader (normal)

That is ~696 GStreamer playbin/GL pipelines that were never freed — almost exactly one per bell rung. The leaked threads are parked in __futex_wait (0 nonvoluntary ctx switches), but the ~1358 GL display event loops still burn multiple cores.

Root cause (from source)

ringBell allocates a fresh MediaFile on every bell:

• src/apprt/gtk/class/surface.zig:2489 → media.fromFilename(path) → gtk.MediaFile.newForFilename(path)
• On Linux the default GTK media backend is GStreamer, and libgstgtk4 wires the playback through a GL sink — so even an audio-only .oga spins up a gstglcontext + gldisplay-event thread set per pipeline.

Cleanup relies solely on notify::ended → unref (src/apprt/gtk/media.zig:96-102). Critically, the error handler is connected only when required == true (src/apprt/gtk/media.zig:50-58):

if (required) {
    _ = gobject.Object.signals.notify.connect(media_file, ..., .{ .detail = "error" });
}
// "ended" handler always connected; calls media_file.unref()

So for an optional bell-audio-path (the common case), any MediaFile that errors or never reaches the ended state is never unref'd, and its pipeline + GL threads leak. The ~696 leaked sets ≈ the number of bells fits this. (A happy-path teardown leak in the GStreamer GL backend is also possible and would compound it — see "Open question".)

The 100 ms per-surface BEL rate-limit (#9810, present since 1.3.0) caps the acute DoS freeze but does nothing for this slow per-bell leak, since legitimate bells fire far below 10/s.

This is the same gtk_media_file_new_for_filename-per-bell path implicated in the crash in #11720 (missing playbin3), and any teardown/unref fix should be checked against the GTK ownership double-free discussed in #12306.

Expected Behavior

Ringing the audio bell N times leaves the thread/pipeline count bounded (ideally constant), and idle CPU returns to baseline after playback finishes.

Actual Behavior

Each audio bell leaks a GStreamer pipeline and its GL threads. Thread count and idle CPU grow without bound over the lifetime of the process.

Reproduction Steps

1. Config: bell-features = audio + a valid bell-audio-path.
2. Spam bells, spaced past the 100 ms rate-limit:

   while true; do printf '\a'; sleep 0.2; done
   

3. Watch the thread count climb and not recover:

   watch -n1 'ls /proc/$(pidof ghostty)/task | wc -l'
   

Ghostty Logs

No response

Ghostty Version

Ghostty 1.3.1-arch2

(Code path is unchanged on tip — the 79162279d "enabling reuse" refactor only relocated the helpers; the bell call site still allocates a new MediaFile per ring.)

OS Version Information

Arch Linux. GTK 4.22.4, libadwaita 1.9.0, GStreamer 1.28.3 (gst-plugins-base/good 1.28.3). Default (GStreamer) GTK media backend (GTK_MEDIA unset); libgstgtk4.so present.

(Linux only) Display Server

Wayland

(Linux only) Desktop Environment/Window Manager

No response

Minimal Ghostty Configuration

bell-features = audio,attention,title,border
bell-audio-path = /path/to/bell.oga

Additional Relevant Configuration

Triggered in practice by long-lived TUI programs that ring the bell on each completion (e.g. AI coding agents), accumulating hundreds of bells over a multi-day session.

Suggested fixes

• Reuse a single MediaFile per surface (seek(0) + play() on each bell) to bound pipelines to 1 per surface regardless of root cause. Note: the Audible ping not working as expected #8957 "plays only once" bug was reuse without seeking back to start, so seek(0) is the key detail.
• And/or connect the error handler unconditionally so the optional-audio path also tears down.
• Longer term, consider a non-GStreamer bell (e.g. libcanberra / direct PipeWire) to avoid the GL pipeline entirely.

Open question for maintainers

Does the leak occur on the happy path (i.e. does the GStreamer GTK4/GL backend fail to join gstglcontext/gldisplay-event threads even when ended fires and unref runs), or only on the error/never-ended path? The fix scope depends on this. A minimal GTK4 harness that loops new_for_filename → play → await ended → unref while sampling g_type_get_instance_count(gtk_media_file_get_type()) (GOBJECT_DEBUG=instance-count) and /proc/self/task would disambiguate.

[jcollie]

#13647