multi: Small Determinism Fixups#308
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The payment event heap previously ordered events by execution time alone. When two events are scheduled for the same instant, the BinaryHeap pop order was unspecified, making otherwise-seeded runs non-reproducible. Break ties on the source node's public key. The heap holds at most one event per source at a time, so (execution_time, source) is a total order, and Eq is made consistent with the new Ord. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Two select! loops still polled their branches in tokio's default random order: the payment-failure result send in produce_simulation_results, and the interceptor-result drain in the SimNode HTLC forwarding path. Random branch selection is a source of run-to-run non-determinism. Make both biased so their poll order is fixed. Branch order is unchanged, so behaviour is identical save for the now-deterministic ordering. The shutdown listener already sits first in the failure-send loop, matching the shutdown-first convention used elsewhere. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
send_payment stamped each Payment's dispatch_time with SystemTime::now(), bypassing the simulation clock. Under discrete-event simulation the wall clock does not advance with virtual time, so this both broke virtual-time timestamps and made results non-reproducible. Stamp the dispatch time from the simulation clock once the inter-payment wait has elapsed, and thread it into send_payment as an argument. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The latency interceptor sampled its forwarding delay from rand::thread_rng(), an unseeded global RNG. That made HTLC latencies non-reproducible even when the simulation was given a fixed seed. Hold a seedable StdRng on the interceptor (behind a mutex, since it is shared across concurrent HTLCs) and seed it from the new_poisson constructor. The CLI threads its fixed seed through when building the interceptor. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
elnosh
approved these changes
Jun 24, 2026
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A few low hanging fruit for improving determinism courtesy of claude.