[riccardosabatti]

Why. map.flyitalyadsb.com moves every 2 s at best (every 3–4.5 s over London, a user's screen recording on 2026-11-02, fixed separately in flyitalyadsb/tar1090#5). The map reads the readsb API (--tar1090-use-api), and apiUpdate rebuilds the API buffer every --write-json-every. Lowering that also rewrites aircraft.json and the 577 globe files every round: ~8.4 MiB, 4.2 MiB/s per cell today at 2 s, on a VM disk already writing ~25 MiB/s. The API update alone is cheap: api_update ≈ 0.04 core at 2 s (stats.json last15min).

Change: --api-update-every <sec>

• apiUpdateEntryPoint waits api_interval instead of json_interval.
• apiUpdate wakes the json writers (Threads.json, Threads.globeJson) once per json interval only, so the files keep --write-json-every. With equal intervals it wakes on every update, as upstream.
• With --tar1090-use-api, receiver.json refresh is the API rate, which is what tar1090 polls (RefreshInterval = data.refresh).
• Default = --write-json-every. Longer is clamped with a warning, since the API update is what wakes the writers.
• The WITH_UUIDS recent-receivers window follows the update interval.

Readers of the double buffer (API workers, the two json writers) copy from the flipped buffer in milliseconds. A flip every 0.5 s gives them the same margin upstream gives at --write-json-every 0.5.

Test. flyitalyadsb/test-api-update-every.sh on a real binary, in a new workflow flyitalyadsb-test.yaml. It samples the API's now and aircraft.json's now for 8 s and takes the median gap between readsb's own timestamps:

• 0.5 / 2 s: API every 0.5 s, aircraft.json every 2 s, refresh 500;
• no option: both every 2 s, refresh 2000 (upstream behaviour);
• --api-update-every 5 with 2: refresh 2000 and the warning.

Run locally, because CI can't run here: ubuntu:24.04 container, make (gcc, -Werror) + upstream make test + the new test:

api-update-every 0.5, write-json-every 2: API every 0.50 s, aircraft.json every 2.00 s
write-json-every 2 only: API every 2.00 s, aircraft.json every 2.00 s
ok

Negative check: with the json-wake gate removed (if (1 || …)) it fails with aircraft.json written every 0.50 s, expected 2.

⚠️ Actions is disabled on this repository (gh workflow run → HTTP 422 "Actions has been disabled for this repository", while actions/permissions says enabled). No run since 2026-10-29 11:52Z: no sync-upstream, no promote, no PR builds. Until it's re-enabled, merging this builds no canary.

Rollout. Merge → readsb-canary:canary on cell B. The option goes into nesso-infra's args only once cell A runs a stable that knows it, because an unknown option stops readsb. B first through gen_cell_b.py overrides, then both.