`spinning` was `spin_budget_cycles > 0` alone. At N=1 the pool-size cap is 0, so
spinning was enabled while no scheduler could ever enlist: n_spinning pinned at 0,
so the enqueue submit-rule guard (n_spinning==0) fired a wake-nobody futex_wake on
every push. Now gated on `budget > 0 && max_spinners > 0`; a debug_assert guards
the invariant against regression. No behavioural change (a 0-cap runtime never
parks on the futex either way) — single_thread_spinning_is_inert and the AllDone
liveness test (shutdown_releases_pinned_parked_siblings) still pass.
switch_cost N=1 (1-core sandbox): p50 ~466ns -> ~186ns. The wake-nobody syscall
was ~60% of the round-trip in wall-clock terms; the handoff's "~12%" was perf
self-time, not latency share. ROADMAP per-switch section updated to fold in the
N=1 spike correction (shim hypothesis is many-core only). Dropped the throwaway
budget_probe bench (switch_cost reproduces every state via .spin_budget_cycles/
.max_spinners and with percentiles).
The terminal-wake fix cannot reach the (deadline, no-io) idle branch:
thread::sleep, no pipe to write. Documented as a Later item with the
two candidate mechanisms (clamped sleep vs condvar/futex), plus the
cross-thread-unpark observation from the same session.
Shootout (6d9f369 harness, 24-core sweep) landed in RFC 005's World 3:
queue variants indistinguishable in rq_runtime; per-wake latency is the
ceiling. Record the queue-topology closure (rq-mutex frozen as default,
benchmark-driven reopening only), define v0.9 as the wake-path latency
cycle (RFC 005 slot -> bench -> RFC 004 spinning workers -> bench +
interaction pass), and add per-switch cost to Later pending a profiling
spike + RFC.
Completed cycles compacted to the two trailing minors (v0.7, v0.8);
earlier history lives in git.
Gotchas now lead with the consuming-wake invariant ('the only wildcard wake
is request_stop') and the obligations it puts on future wakers. Deviations
recorded: the no-park exit's retire_wait/clear_notify (a protocol piece the
plan missed), Drop-guard deregistration superseded by own-pid assert
relaxation, and closed arms being ready forever.
Marks the three v0.6 items done with their hashes and the load-bearing
deviations: two-class lock order replacing the strict leaf rule, the
registry as a bimap with name_of and without send_by_name (no per-pid
mailbox to send to), and call_timeout built on recv_timeout instead of
monitor machinery. Adds the Leaf -> Channel order to the standing
invariants; README module table picks up recv_timeout, call_timeout,
and the registry row.
smarm-agent