heartbeats

heartbeats

Dynamic peer-runtime federation. Workers register, take work via agent.delegate, send heartbeats, and deregister cleanly. Heartbeat loss reroutes the in-flight task to another worker — deduped by idempotency_key.

Before ARCP

Static worker pools with bespoke RPCs. The supervisor's "is this worker alive?" answer comes from a TCP keepalive (lies during GC) or a custom heartbeat that re-dispatch logic doesn't actually trust — so re-dispatch either fires too eagerly (duplicate execution) or not at all (stuck pipeline).

With ARCP

function reaper(ARCPClient $sup, Roster $roster, array &$jobs): void
{
    while (true) {
        delay(HEARTBEAT_INTERVAL_SECONDS);
        foreach ($roster->workers as $w) {
            if (stale($w)) {
                if (($jid = $w->inFlightJob) !== null && isset($jobs[$jid])) {
                    dispatch($sup, $jobs[$jid], $roster, $jobs); // same key
                }
                unset($roster->workers[$w->workerId]);
            }
        }
    }
}

idempotency_key makes re-dispatch safe: a worker that survived the network blip will see the duplicate agent.delegate and dedupe.

ARCP primitives

• Capability negotiation (per-role extension) — RFC §7, §21.
• agent.delegate — §14.
• Job lifecycle (accepted → started → heartbeat → terminal) — §10.
• Heartbeat loss recovery — §10.3 (heartbeat_recovery: "block").
• idempotency_key for safe re-dispatch — §6.4.
• Trust levels — §15.3.

File tour

• main.php — boots supervisor + small worker pool in-process. dispatch, reaper, execute all live here.
• work.php — doWork() payload-handler stub.

Variations

• Priority queues by tagging tasks with envelope priority.
• Per-worker quota tracked via tokens.used metrics emitted from worker sessions (RFC §17.3.1).
• Replace the in-process workers with separate processes on real hosts; the protocol shape doesn't change.