The polling thread owns the ELM327, so reading/clearing trouble codes from
the GUI thread would race PID reads and corrupt the stream. Add a one-off
command path that serializes ad-hoc link work onto the polling thread.
obdcore/scheduler.py:
- PollScheduler.run_oneoff(fn, timeout) enqueues a callable (queue.Queue +
threading.Event) and blocks for its result, re-raising the callable's
exception. tick() drains queued one-offs at its very top, so they run on
the same thread that does PID reads -- never concurrently. When the
scheduler thread isn't running, the job is drained inline on the caller
(still serialized vs tick(), safe because nothing else touches the link).
gui/controller.py:
- Controller.read_dtcs() -> {"stored","pending","permanent"} (modes 03/07/0A,
svc 0x43/0x47/0x4A) and clear_dtcs() -> bool. Both route through the
scheduler one-off when a scheduler exists, else call the link directly.
gui/main.py:
- Diagnostics menu (Read Codes / Clear Codes...) and a right-side QDockWidget
listing codes grouped Stored/Pending/Permanent. Each row is code +
description + system from DtcDatabase; no_start codes are flagged bold red.
- Clear is guarded by a confirmation warning (erases codes + freeze frame;
honest "the code comes right back" / permanent-codes-won't-clear tone from
run_clear in obd_reader.py). On confirm: clear, then re-read immediately and
show whatever returned, reporting active faults that came straight back.
tests/test_diagnostics.py:
- one-off returns its value, re-raises exceptions, is drained before a tick's
PID reads, and runs on a live background thread while polling continues.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016yT89n4zR4qbrySoSiEyZs
