fix(iouring): read a worker's clock on every CQE batch, as epoll does, so a live connection is not timed out on a stale stamp (celeris#713)

[FumingPower3925]

Summary

An io_uring worker stamps lastActivity (at accept, at every recv, at every send completion) from w.cachedNow. checkTimeouts compares those stamps with a fresh time.Now() and reads the difference as idle time. The worker read cachedNow only on every 64th iteration that carried CQEs, plus in checkTimeouts. An idle or paused worker waits up to 100 ms or 1 s per iteration, so its stamps could be seconds old, and the whole park older still. Past ReadTimeout, the engine closed a connection in the middle of steady traffic, with a request already written.

The issue measured it through the adaptive engine: 6 of 6 promotes that came 31 s after a demote, ReadTimeout 30 s. It named the park as the trigger and said the class might be wider.

Round 2. Round 1 read the clock again on leaving the park and stamped an adoption with a fresh clock. The review showed the class is wider, as the issue said, and round 1 did not cover the rest. The same close reproduced deterministically with no park:

• on a running idle worker with ReadHeaderTimeout off;
• on a paused worker that still holds a connection;
• on an adoption onto such a worker.

The worker now reads the clock once per CQE batch, after the wait that delivered it, as epoll does on every events-bearing epoll_wait return.

Fixes #713

Measured first

Docker linux/arm64, 4 CPUs, go test -v. m8 is CI's 8 MiB memlock (one io_uring worker); unl is unlimited memlock (two workers). ReadTimeout = WriteTimeout = 2 s in every arm, and every request gap is well inside it.

test	shape of the worker	control
TestAcceptAfterALongParkIsNotTimedOut	parked 3 s, woken by ResumeAccept and a dial; 20 requests 100 ms apart	TestAcceptAfterAShortParkIsNotTimedOut (100 ms park)
TestAdoptAfterALongParkIsNotTimedOut	parked 3 s, woken by AdoptConn (the reclaim onto a draining source; an adaptive promote resumes the new active engine before it adopts, which is the accept arm's shape)	none (TestAdoptAfterAShortParkIsNotTimedOut fails on main too)
TestIdleWorkerWithoutAHeaderTimeoutIsNotTimedOut (new)	running, idle 5 s, ReadHeaderTimeout off (checkTimeouts every 1024th iteration); 20 requests 500 ms apart	TestIdleWorkerWithAHeaderTimeoutIsNotTimedOut (the default ReadHeaderTimeout: every 32nd, with waits of at most 25 ms)
TestPausedWorkerWithALiveConnectionIsNotTimedOut (new)	paused while it holds the connection, so it never parks; 30 requests 300 ms apart	TestPausedWorkerWithABusyConnectionIsNotTimedOut (100 ms apart)
TestAdoptOntoADrainingWorkerIsNotTimedOut (new)	paused 3 s, kept from parking by a registered driver connection on each worker, then AdoptConn; 20 requests 100 ms apart	none
TestAdoptionIsStampedWithTheTimeItWasAdopted	unit: the adoption stamp on a worker whose clock is injected 1 h stale	none

test	main's engine code (713-r3neg, m8, 10 runs)	round-1 fix	this head 9fb68fe (m8, 10 runs)
accept, 3 s park	FAIL 10/10: EOF on request 2	PASS (round 1)	PASS 10/10
adopt, 3 s park	FAIL 10/10: request 13-15 times out	PASS (round 1)	PASS 10/10
accept, 100 ms park (control)	PASS 10/10	PASS	PASS 10/10
adopt, 100 ms park	FAIL 10/10: request 13-15 times out	PASS (round 1)	PASS 10/10
idle worker, ReadHeaderTimeout off	FAIL 10/10: EOF on request 11 or 12	FAIL 4/5 (05a5cfe)	PASS 10/10
idle worker, default ReadHeaderTimeout (control)	PASS 10/10	PASS 5/5	PASS 10/10
paused worker, requests 300 ms apart	FAIL 10/10: request 14 or 15 times out	FAIL 5/5	PASS 10/10
paused worker, 100 ms apart (control)	PASS 10/10	PASS 5/5	PASS 10/10
adoption onto a draining worker	FAIL 10/10: EOF on request 12 or 13	FAIL 10/10	PASS 10/10
unit, 1 h stale clock	FAIL 10/10	PASS	PASS 10/10

• The main and round-1 columns are the failing-first. 713-r3neg is this head with worker.go and transplant.go cp'd from main 698bed6, so it also serves as the negative control.
• The round-1 fix is 05a5cfe (the new arms on round 1's engine). For the draining-adoption arm it is 05a5cfe with this head's test file, because the arm's rig changed (below).
• "PASS (round 1)": the round-1 fix passed those arms in round 1's logs (logs/verify2-m8/, logs/unl-all/).
• A timeout rather than an EOF means that the close was the worker's last and the worker then parked. That is io_uring: a sync-mode HTTP/1 connection closed in the iteration that parks a paused worker gets no FIN until the worker wakes (the cancelled recv still holds the file; argued: its DEFER_TASKRUN completion needs a GETEVENTS enter the park never makes) #712, from a second direction.

In unl (two workers, logs/rv2-unl3/, 5 runs each):

• this head passes all ten tests 5/5, plus 10/10 more on the draining adoption;
• main's engine fails every stale arm 5/5, except the idle arm without RHT, which fails 4/5 (one run passed). Its controls pass 5/5;
• the round-1 fix fails the draining adoption 10/10. At 05a5cfe it failed the idle arm 2/3 and the paused 300 ms arm 3/3 (logs/rv2-unl/713-round1.log).
• The draining-adoption arm's rig changed in d3e46c3. It first kept every worker from parking with 16 idle keep-alive holders. With two workers (unl), ReadTimeout closed one worker's holders during the 3 s wait whenever that worker's checkTimeouts came due, and the worker parked: a failed premise in 4 of 15 unl runs, on the fix and on main's engine alike, and in none of 50 at m8 (logs/rv2-unl/, logs/rv2-m8b/). A registered driver connection on each worker now keeps it from parking. No timeout touches a driver connection, and while idle it completes nothing, so the worker's clock goes stale as before. 9fb68fe changes only a comment, the one that quoted that count.

The fix

• worker.go, the CQE batch: w.cachedNow = time.Now().UnixNano() on every CQE-bearing iteration, where it was gated on tickCounter&0x3F == 0. Every stamp the batch takes is then no older than the batch. epoll made the same change in v1.5.0 (7beebb9); its comment in engine/epoll/loop.go reads "The vDSO cost (~50ns) is negligible amortized over the whole event batch".
• The park-exit read is gone. Round 1 added it; the first stamps after a park now come from a CQE batch (an accept's CQE, or the adoption's eventfd wake), which reads the clock. MNOBATCH below is round 2's fix without the per-batch read, and it fails the long-park arms. So the per-batch read is what covers the park, and a second read on waking would add nothing that any arm can see.
• attachAdoptedFD keeps its fresh stamp (round 1), with its comment corrected. No engine-level arm needs it (MNOSTAMP below), because the adoption's eventfd wake is a CQE of the same iteration. It covers an adoption drained in an iteration that carried no CQE. The unit test pins it. It costs one vDSO call per adopted connection.

Controls

Second controls, each overlaid on the fix with go test -overlay (rv2/mkmutants.sh, rv2/mutants/); m8 unless noted:

mutant	result
MNOBATCH: the CQE-batch read gated on tickCounter&0x3F again, main's cadence without round 1's park-exit read	FAIL 5/5 on every arm that fails on main: accept 3 s, adopt 3 s, adopt 100 ms, idle without RHT, paused 300 ms, draining adoption. The three controls and the unit test PASS 5/5.
MNOSTAMP: the adoption stamped from w.cachedNow again	every engine arm PASS 5/5 (accept 3 s, adopt 3 s, adopt 100 ms, draining adoption); the unit test FAILS 5/5
GAP250, GAP1500: the park arms' request gap 250 ms or 1500 ms, against ReadTimeout 2 s	GAP250: all five adoption and park arms PASS 5/5. GAP1500: adopt 3 s and draining adoption PASS 3/3. The round-1 head failed its adopt 3 s arm 5/5 at 250 ms (the review's GAP250).
MEPOLL63: epoll's per-return clock read gated on &0x3F, the pre-7beebb9 cadence	both epoll twins FAIL 5/5 (EOF on request 2). Without the mutant they PASS 5/5.

• MNOBATCH is the proof that the per-batch read is the fix, and that it covers the park: with it removed, the park arms fail as on main.
• MNOSTAMP shows what the adoption stamp does and does not do: no engine arm needs it, and the unit test pins it.
• The GAP runs show the margin. With the per-batch read, a connection's apparent idle time follows the client's gap, not the worker's iteration count.
• MEPOLL63 answers the review's point that the epoll twins pass on main by design: they can fail.
• Mutant runs: MNOBATCH and MNOSTAMP on the draining-adoption arm at 9fb68fe (logs/rv2-m8c/); the others at 6267e56 (logs/rv2-m8b/). 6267e56..9fb68fe changes only park_stale_clock_test.go: that arm's rig and one comment.
• -race: the ten tests at m8, count 3: PASS 30/30.

The A/B through the adaptive engine

Round 1 ran the probatorium#416 revert-cell job-2 design: the adaptive engine through the public API, 100 hot keep-alive clients, 20 idle ones, 10 slowloris, 10 late talkers, every switch after the natural promote forced, Workers 2, unl. The windows are the issue's recount (713/ab_recount.py). What decides each arm is how long the io_uring standby parks: gap minus stby0_s, the time from the demote until the standby's last connection is gone.

The base binary is main's engine code (698bed6), unchanged since round 1. probe-fix2 is built from 6267e56, whose production code this head keeps, by the committed 713/probe/build.sh (-trimpath; 713/probe/bin-rv2/BUILD.txt, SHA256SUMS). Round 1's probe-fix is the round-1 fix.

arm (promote gap after the demote, ReadTimeout, mode)	park	main: closes +100 ms / client failures in 5 s	round-1 fix	round-2 fix
A (25 s, 30 s, async)	~14 s	1 / 0	1 / 0	1 / 0
B (35 s, 30 s, async)	~24 s	3 / 0	2 / 0	not run
C (35 s, 60 s, async)	~24 s	2 / 0	0 / 0	not run
B (35 s, 30 s, sync)	~33 s	153 / 139	0 / 0	1 / 0
B (35 s, 30 s, sync), replication	~33 s	128 / 115	2 / 0	1 / 0
D (45 s, 30 s, async)	~34 s	120 / 120	1 / 0	1 / 0

• On main, every arm whose park outlasted ReadTimeout failed (3/3), with 115-139 client requests failing within 5 s of the promote.
• With either fix, none did. Round 2 ran the three failing arms and one control: 0/4 with failures.
• In the round-2 runs, every demote, including each run's second one (the epoll twin), had 0 client failures, and the background (the largest 100 ms close count in the 5 s before the promote) was 11-13.
• The table is logs/rv2-ab/RECOUNT.txt (rv2/ab_recount.py: round 1's recount, with the round-2 runs added).
• The issue's async 31 s closes on 9f4d89b. The review found the explanation, using the lane's recount on the issue's raw files: on 9f4d89b the async standby emptied about 1 s after the demote, not the ~11 s it takes on main, so the park was about 30 s. Which change moved it is a follow-up (Follow-ups from #768: named CI interlocks for the #713 tests and epoll twins, and why the async standby's drain grew from ~1 s to ~11 s #797).

Suites

go test -race -count=1 -v, one package per go test, Docker linux/arm64. Tallies count every verdict line, subtests included.

engine/iouring	m8	unl
main 698bed6, the branch's base (round 1: logs/verify-m8/, logs/unl-all/)	PASS 318, FAIL 0, SKIP 5	PASS 321, FAIL 0, SKIP 2
this head 9fb68fe (logs/rv2-m8c/, logs/rv2-unl3/)	PASS 328 (+10 tests), FAIL 0, SKIP 5	PASS 331, FAIL 0, SKIP 2
current main dfd044f	PASS 339, FAIL 0, SKIP 5	PASS 342, FAIL 0, SKIP 2
dfd044f merged with #766, #767 and this head	PASS 357, FAIL 0, SKIP 5	PASS 360, FAIL 0, SKIP 2

• The SKIPs have the same names everywhere: the two synack tests, plus at m8 the three celeris#656 init-failure tests.
• No data race in any run. The ten io_uring: a parked worker keeps a stale cachedNow; if the park outlasted ReadTimeout, conns it adopts or accepts on waking get a past timestamp and the first checkTimeouts closes them (adaptive: 6/6 promotes 31 s after a demote, 0/8 at 18 s; A/B not run) #713 tests under -race at m8, count 3: PASS 30/30.
• engine/epoll: this branch changes only its test file there, which is identical at 6267e56 and 9fb68fe. At 6267e56: PASS 154 (+2 twins), FAIL 0, SKIP 3 in both shapes; main 698bed6 gives 152/0/3. On the merged dfd044f tree at m8: PASS 156, FAIL 0, SKIP 3.
• Named tests together: the io_uring tests of all three PRs on the merged dfd044f tree, -race, m8, count 2: PASS 36/36.
• ./adaptive/... (-race, unl) on the merged dfd044f tree: PASS 115, FAIL 0, SKIP 0. Main dfd044f gives the same, PASS 115.
• Static checks (rv2/lint.sh, logs/rv2-lint/): build, vet, test -c and golangci-lint 2.13.2 for linux amd64 and arm64. All 10 steps rc=0 on this head and on the merged tree.
• amd64 under Docker's emulation: vet and test -c rc=0 (logs/rv2-amd64-3/). The ten io_uring tests SKIP, because io_uring is not available there; a SKIP is absent, not a pass. The epoll twins PASS 2/2 (logs/rv2-amd64/quick-713-epoll.log, at 6267e56).
• CI at 9fb68fe: 17/17 green (CI run 36373920043). Attempt 1 failed one test outside this change, TestDriverLingeringCloseDoesNotStallTheWorker/linger (fix(iouring): close a driver conn's engine descriptor off the worker, and fire onClose after the close (celeris#735) #744's rig, merged to main half an hour earlier). Its log line: "L's onClose fired while its close still lingered", with onclose_after_finalize_ms=100.5, the no-linger control's value.
  • The same test passed on attempt 2, and in CI run 36373195106 on d3e46c3, which merged into the same main f0886ca. d3e46c3..9fb68fe changes one comment in a test file.
  • Reported on Follow-ups from #744: parallel driver closes at shutdown, onClose no longer tied to the fd's map removal #763, the fix(iouring): close a driver conn's engine descriptor off the worker, and fire onClose after the close (celeris#735) #744 follow-up.
  • In the Unit job's engine/iouring step all ten io_uring: a parked worker keeps a stale cachedNow; if the park outlasted ReadTimeout, conns it adopts or accepts on waking get a past timestamp and the first checkTimeouts closes them (adaptive: 6/6 promotes 31 s after a demote, 0/8 at 18 s; A/B not run) #713 tests PASS with no SKIP (ci/rv2/unit-36373920043-a2.log).

Cost

The per-batch read is on the request path, so it was measured, not argued. rv2/bench.sh ran under the laptop's timing lock (no other container), in Docker linux/arm64 with 4 CPUs.

• Method. An engine (two workers) serves keep-alive clients that send one request and read its response, b.N requests in all. The benchmark file is overlaid, not committed (rv2/bench/ep2_clock_bench_test.go).
• Arms. A is this head. B is this head with the &0x3F cadence restored (MNOBATCH). Nothing else differs.
• Runs. The order was A B B A, five times: 10 runs per arm, -benchtime=2s. The comparison is benchstat (logs/rv2-bench/benchstat.txt).

benchmark	&0x3F (B)	every batch (A, this head)
time.Now().UnixNano()	34.02 ns ± 2%	33.99 ns ± 3%	the added call
one client, ping-pong	20.86 µs ± 10%	19.58 µs ± 26%	~ (p=0.123)
16 clients	2.447 µs ± 11%	2.459 µs ± 6%	~ (p=0.724)

• No significant change in either shape.
• An upper bound from the counts. An overlay that counts CQE batches (rv2/bench/COUNT, not timed) measured 2.000 batches per request with one client and 0.693 with 16 (logs/rv2-bench/count.txt). The added cost is therefore at most 2.0 × 34 = 68 ns per request (0.35% of 19.6 µs) and 0.69 × 34 = 24 ns (about 1% of 2.46 µs). That is below what the laptop can resolve (±6-26%).
• A cluster timing row is queued for bare metal.

Relation to #711 and #712

This branch no longer touches the park branch; its only worker.go hunk is the CQE batch. All three heads merge cleanly onto current main dfd044f, pairwise and in all six orders, into one tree, 421e683 (rv2/merge_check.sh, logs/rv2-merge.txt). Their named tests pass together on the merged tree, and the package suites and ./adaptive/... pass there too (above).

On bare metal

Rows in evidence/_queue/cluster.tsv (lane EP-2):

• The arms on bare metal: 9fb68fe, native io_uring with two workers, both arches, -race. Every celeris713 line must read failed_at=-1. The ebbeda6 row is superseded.
• The cost on bare metal: the two keep-alive benchmarks through a timing wrapper (rv2/bench/zz_bench713_wrapper_test.go), A against B on msa2-server and msr1. PASS is no significant change (±2%). It needs the two wrapper refs pushed.

Evidence

evidence/lanes-20260927/EP-2/: round 2 is rv2/ (mkmutants.sh, jobs/, bench.sh, bench/, results.py, whose output is rv2/RESULTS.md, ab_recount.py and merge_check.sh) and 713/probe/build.sh, with logs in logs/rv2-*/. Round 1 is described in README.md.

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📝 Walkthrough

Walkthrough

io_uring refreshes its cached clock when it receives a nonempty CQE batch and timestamps adopted connections with the current time. New tests exercise parked and active worker scenarios in io_uring and epoll.

Changes

Connection Timeout Timestamps

Layer / File(s)	Summary
io_uring worker clock and timeout scenarios engine/iouring/worker.go, engine/iouring/park_stale_clock_test.go, engine/epoll/park_stale_clock_test.go	The worker refreshes cachedNow for each nonempty CQE batch. Tests cover accepted and adopted connections after parks, active and draining workers, and epoll accept and adoption after a long park.
Adopted connection timestamp engine/iouring/transplant.go, engine/iouring/park_stale_clock_test.go	attachAdoptedFD sets lastActivity from the current time. A test checks the timestamp when the worker's cached clock is stale.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description directly explains the stale io_uring worker-clock bug, the per-CQE-batch refresh, the adoption timestamp, regression tests, and measured validation.
Title check	✅ Passed	The title follows the required conventional-commit form, describes the main io_uring clock-refresh fix, and ends with the issue reference (celeris#713).
Linked Issues check	✅ Passed	Issue #713 requires prevention of stale lastActivity timestamps after io_uring waits, parks, and adoptions. engine/iouring/worker.go refreshes cachedNow after each CQE-bearing wait before handli…
Out of Scope Changes check	✅ Passed	All changed files support issue #713. The worker and transplant changes implement the stale-clock fix. The io_uring tests verify the affected timing paths. The epoll tests verify the issue's requested…

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Review comments at @engine/iouring/park_stale_clock_test.go:
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