A message sent before the stop flag is observed must be delivered and run
before the engine stops. One rule; a spin count could never express it.
- root cause in `shard_main` (runtime/src/vm.c): NEXT_RUNNABLE() already
stated the contract — "a WORKER on stop keeps DRAINING ... so queued
shutdown messages (close frames!) still run" — but the IDLE branch
contradicted it, calling fib_reap_all and breaking on WO_IO_STOP,
abandoning its inbox for wo_engine_stop() to free wholesale
- an actor between messages is exactly that idle case, which is why a WARM
soak server hid it: warm shards held live fibers and took the right path
- fix: while the primary's drain window is open, an idle worker adopts its
inbox and runs what arrives; sched_yield on an empty poll so a drain
cannot burn a core per shard and starve the actors it exists to let run
- unreachable at WO_SHARDS=1: wo_engine_stop returns early at nshards <= 1
Measured:
- fresh-server SIGTERM drain: 5 of 16 failing before, 20 of 20 clean after
- `just chat` at the FULL 1000-client soak: 11 checks, 0 failures, both
WO_IO backends, ASan clean with zero leaks
- the fd leg settled at scale too: 1000 connections left the count at 44,
unchanged after 20 more — lazy per-shard init, not a leak
- runtime battery 36 suites (18 x both dispatch flavors) 0 fail;
compiler 556 checks 0 fail
- story: docs/stories/language-runtime-database/40-shutdown-drain-guarantee.md
(chain 3 with 31, status done), board row, slice marker updated
- outstanding and named: a pin below the gate needs new multithreaded test
infrastructure — nothing in runtime/test/ drives wo_engine_start/stop and
no corpus fixture can trigger a stop
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
