248 Days to Reboot — Java Bug Hunt

Briefing

Inspired by the Boeing 787 directive ordering a power cycle at least every 248 days — the generator control units kept an internal counter in hundredths of a second, in a 32-bit signed integer. 2,147,483,647 centiseconds ≈ 248.55 days. Then it wraps negative.

Uptime.java does the same conversion — in int.

Bug report

BUG-787 · Priority: Critical (airworthiness) · Reported by: systems review

centisAfterDays(days) must be exact for mission-length uptimes:

• 300 days = 2,592,000,000 centiseconds — bigger than any int.

Observed: 300 days comes back NEGATIVE, and the watchdog logic downstream treats the system clock as corrupted.

Logs

[gcu] uptime(300d) = -1702967296 centis
[gcu] watchdog: clock corruption suspected -> failsafe

The code as shipped

Uptime.java (editable)

class Uptime {
    static final int CENTIS_PER_DAY = 24 * 60 * 60 * 100;

    // Total centiseconds of uptime after the given whole days.
    static long centisAfterDays(int days) {
        int total = days * CENTIS_PER_DAY;
        return total;
    }

    // True once uptime exceeds the mandated safe window.
    static boolean rebootRequired(long centis) {
        return centis >= 248L * CENTIS_PER_DAY;
    }
}