Before this change, calculate_packet_hash() (SHA-256 + hex + upper) was called
3 times per forwarded packet and 4 times per dropped packet:
__call__ → pkt_hash_full = packet.calculate_packet_hash() #1
→ flood/direct_forward → is_duplicate → calculate_packet_hash() #2
→ flood/direct_forward → mark_seen → calculate_packet_hash() #3
(drop) → _get_drop_reason → is_duplicate → calculate_packet_hash() #4
pkt_hash_full was computed in __call__ but never threaded down into
process_packet, flood_forward, direct_forward, is_duplicate, or _get_drop_reason.
Each method recomputed it independently.
Fix: add optional packet_hash: Optional[str] = None to is_duplicate,
_get_drop_reason, flood_forward, direct_forward, and process_packet. Pass
pkt_hash_full from __call__ through the chain. Each method uses the provided
hash or falls back to computing it — preserving backward compatibility for
external callers (TraceHelper, etc.) that have no pre-computed hash.
Result: 1 SHA-256 computation per packet in the hot path regardless of whether
the packet is forwarded or dropped.
Also adds explicit INVARIANT docstrings to flood_forward, direct_forward, and
is_duplicate documenting that these methods must remain synchronous (no await).
The is_duplicate + mark_seen pair is atomic within the asyncio event loop; adding
an await between them would allow two concurrent tasks to both pass the duplicate
check for the same packet — forwarding it twice.
Docs: docs/pr_hash_once.md — problem analysis, call-chain diagram, per-method
diffs, quantification (~3-8 µs saved per packet), test plan (including hash-count
assertion), and proof that passing the original's hash to the deep-copied packet
is correct.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Replace the _route_tasks set in PacketRouter with a simple integer counter
(_in_flight / _max_in_flight=30) and add an early-drop guard in _process_queue.
Problems solved:
1. No cap on concurrent sleeping tasks: burst arrivals (multi-hop amplification,
collision retries) could stack unbounded _route_packet tasks, each holding a
packet closure and asyncio Task overhead, before the duty-cycle gate fired.
2. _route_tasks set held a strong reference to every Task object for the full
duration of its sleep — unnecessary in Python 3.12+ where the event loop
already holds tasks alive.
3. stop() iterated the full set to cancel tasks on shutdown — O(n) where n is
the in-flight count at shutdown time.
Fix: _in_flight counter increments before create_task and decrements in the
_on_route_done callback. The cap check (>= 30) in _process_queue is a last-resort
safety valve — LoRa airtime and the duty-cycle gate keep _in_flight in the
low single digits under normal load.
Also lower companion dedup prune threshold from 1000 to 200: the original 1000
allowed stale entries to accumulate for hundreds of PATH packets before the
O(n) dict comprehension sweep ran.
Trade-off documented: explicit task cancellation on shutdown is removed; tasks
are cancelled implicitly by event loop shutdown with identical outcome (no packet
transmits after the radio is closed regardless).
Docs: docs/pr_in_flight_cap.md — full problem analysis, alternative approaches
(semaphore, keep set + add cap), proof of counter sufficiency, rationale for
cap=30, and unit + field test plan.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit sets up the initial project structure for the PyMC Repeater Daemon.
It includes base configuration files, dependency definitions, and scaffolding
for the main daemon service responsible for handling PyMC repeating operations.
