Closing a camera view logged "ffmpeg didn't terminate gracefully,
killing" followed by "ffmpeg did not exit within 2.0s of SIGKILL;
abandoning wait", on every single close. Both waits expired every time,
so teardown took a fixed 4.00s -- and since the firmware allows one
camera connection, that was 4s in which nothing else could use it.
ffmpeg is spawned with stdout and stderr as pipes and the teardown paths
have stopped reading them, so it sits blocked in write() on a full 64 KiB
pipe. SIGTERM cannot be acted on there: the handler only sets a flag that
the main loop polls, and the loop never gets back to the check. SIGKILL
does kill it, but asyncio resolves Process.wait()'s waiter through
_try_finish(), which requires every pipe transport to report
disconnected; paused, unread pipes never reach EOF, so wait() blocks with
returncode already set. A negative-control test shows returncode=-9 at
the instant the abandon fires.
Draining both pipes while stopping the process fixes both halves: 4.00s
becomes ~0.15s. The signal ladder and its bounds stay as backstops, so a
genuinely wedged process still cannot hang a stream, a Stop request or
the janitor.
This corrects _FFMPEG_KILL_TIMEOUT's premise and #2580's conclusion. That
12-hour hang was the unbounded form of this same self-inflicted stall, not
an ffmpeg stuck in uninterruptible I/O -- the process observed doing it
was in state S, which cannot survive a delivered SIGKILL. Bounding the
wait capped the symptom without removing the cause.
Closing an external USB (V4L2) camera view abruptly could leave its ffmpeg
running and holding /dev/videoN open -- LED stuck on, and reopening the view
failed or took 10-30s fighting for exclusive device access. Same class of leak
as #776 (built-in RTSP path), but the external path was never wired into that
fix: external streams registered into none of the _active_streams /
_disconnect_events / spawned-PID registries, so /camera/stop returned
{"stopped": 0} for a live USB stream and the orphan janitor's /proc net matched
only rtsp(s)://bblp: cmdlines. Cleanup ran only via the stream generator's own
finally, which an abrupt disconnect can skip.
- Thread an on_process callback + stop_event through generate_mjpeg_stream into
_stream_usb / _stream_rtsp; register the process before the startup probe so a
process that hangs on a locked device (not just one that exits) is reapable.
- Register external streams into the shared registries under a unique
{printer_id}-ext-{token} id so /camera/stop and cleanup_orphaned_streams find
and kill them; stop_event prevents the reconnect loops from respawning.
- Extend the /proc safety-net scan to also match USB (-f v4l2) ffmpeg, excluding
still-active streams and unrelated ffmpeg.
maziggy