Files
LEDMatrix/test
4d49b0f892 perf(display): snapshot mirror — viewer gating, digest skip, keepalive (#404)
The display service PNG-encoded its frame to /tmp/led_matrix_preview.png
at 5 fps, 24/7 — identical frames, no viewers, per-call imports and a
chmod every write. On the devpi baseline the display service idles at
~92% CPU; this was one of its biggest fixed costs.

- New pure policy (src/common/snapshot_policy.py, unit-tested off-Pi):
  WRITE changed frames at full rate only while a viewer is watching,
  at a 30s idle cadence otherwise; NEVER re-encode unchanged frames —
  bump mtime (os.utime) every 20s instead, keeping the health check's
  snapshot-age liveness proxy (60s threshold in api_v3) green. Cross-
  referencing comments guard the two constants.
- Viewer detection: the web SSE display broadcaster (which only runs
  while browsers are subscribed) touches /tmp/led_matrix_preview_viewer
  each loop; the display service stats it at most 1/s. On viewer
  arrival the write clock resets so the first frame lands within ~1s.
- Hoisted the per-call pathlib/permission_utils imports; directory
  permissions ensured once instead of every frame.


Claude-Session: https://claude.ai/code/session_01FqzC1nzTWL4kaqgMaQZFam

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
2026-07-13 09:28:30 -04:00
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