Converting COMMIT_MODE_WAIT away from a blocking wait removed the only
mechanism that ever detected a commit timing out (the caller's own
pthread_cond_timedwait deadline). Adds a dedicated per-commit-engine
sweep thread that arms an equivalent timeout for async-registered
continuations, resolving FAILED/-ETIMEDOUT within the same
DEFAULT_SYNC_TIMEOUT_MS window the old blocking path used, with no
thread parked to detect it.
Chose a private sweep thread over the shared delaymgr: wiring
delaymgr would touch cluster.c/ha.c (out of boundary) and its 200ms
poll granularity vs the 500ms default timeout would add jitter,
breaking the "identical failure timing" no-regression bar.
Round 1 review rejected a lost-wakeup race: the sweep loop computed
its next-deadline snapshot under lock, unlocked to dispatch, then
slept on the stale snapshot -- a registration landing mid-dispatch
had its broadcast lost (no thread parked on the condvar), so the
sweep thread could sleep on an absent/late deadline indefinitely.
Fixed by holding the lock continuously across scan-then-wait
decisions and always re-scanning immediately before ever waiting
(recheck-then-wait idiom). Round 2 review independently reproduced
the round-1 bug shape against the fix to confirm it actually closes
the race, not just narrows it.
commit_resolve() delivers a registered continuation's outcome exactly
once (idempotent re-resolve), dispatched off-thread via
vtask_enq_classified(VTASK_LIVE_BLOCK) so it never runs inline on the
replication-ACK or iomgr path. Wired into all 6 commit.c-internal
paths that can advance committed_lsn/writable_lsn.
Review caught a real task-graph gap, not a defect: converting
COMMIT_MODE_WAIT away from a blocking wait also removes the only
mechanism that ever detected a commit timing out (the caller's own
cond_timedwait deadline). Nothing yet arms an equivalent timeout for
async-registered continuations, and nothing wires demotion/log-truncation
detection to commit_resolve(FAILED, ...) -- left as-is, a pending async
command during quorum loss would hang forever instead of failing,
which is worse than today. Split into new tasks 1.3 (timeout arming)
and 1.4 (demotion/truncation wiring), renumbered the old concurrency
test to 1.5, and made 3.2 depend on both since its failure/timeout
observable is meaningless without them. design.md's File Structure
Plan updated to reflect that ha.c/persist.c need a narrow touch for
1.4's detection hooks.
commit_submit_async() lets a WAIT-mode caller register a continuation
against an appended LSN instead of blocking on pthread_cond_timedwait,
reusing the existing admission-cap discipline (wait_admit_locked/
wait_release_locked) so the bounded-capacity guarantee carries over
unchanged. Purely additive: no existing call site (repl_wait_majority_ack)
is touched yet -- that switch lands in task 3.2 once commit_resolve()
(task 1.2) exists to drive it.
vtaskmgr gains vtask_class_t (LIVENESS/LIVE_BLOCK/REQ_BLOCK) + a pool-level
blocking reservation: REQ_BLOCK fast-rejects -XCE_ERR_NOT_READY past
n_vcpus-R; LIVENESS never gated (deadlock-freedom). commit_submit folds its
inflight_waits onto the pool via commit_set_pool; production wired in
cluster.c phase2 (vtaskmgr_set_liveness_reserved(R) + commit_set_pool).
Lock order p->lock->ce->lock->blk_lock. Dormant until 3.1. Commit suites
38/30/22/38 green; lib 282/0, controller 196/0, ASAN clean. Phase 1 done.
Two coupled fixes for a live commit-stall (committed_lsn pinned at the own-term
NOOP while a 3-node cluster was durable to LSN 5 — jobs acked but never committed):
bug-991: the WAL catch-up applied_lsn was advanced to lsn+1 (next-to-apply) in
the three live/catch-up apply paths, but recovery/checkpoint/init and the leader's
catch-up streamer treat it as last-held. The over-advertise made the streamer skip
an LSN -> library logOk wedge -> no WalAck. Fixed to last-held (= lsn).
Option A (design reconsideration of REVIEW ISSUE 3): removed the
committed = min(durable-majority, raft_commit_index) ceiling. Under single-writer
the durable-majority watermark is already (term,lsn)-current-term-safe (term-carrying
replication + (term,lsn) reconcile/truncate-before-durable + own-term NOOP gate +
post-election truncate-to-safe), so the library commit_index was a redundant,
starvation-prone gate that pinned committed below the safe durable majority whenever
the library lagged. The durable-majority barrier + own-term writable gate are now
authoritative; raft_commit_index is inert-advisory.
Safety: reviewer-verified the durable-majority watermark is (term,lsn)-safe and
Figure-8 holds via the own-term gate (new RED->GREEN test); bug-851 cannot recur.
Live: commit trace 4->5 + walcompare committed-prefix identical across 3 nodes.
177 unit tests pass.
