fix(nvca): stop the event dispatcher panicking on a closed channel - #1432
fix(nvca): stop the event dispatcher panicking on a closed channel#1432balajinvda wants to merge 2 commits into
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The dispatcher received events with a single-value receive. A closed channel yields the zero value immediately and forever, so once the event channel closed the dispatcher dereferenced a nil event and panicked, and span on the closed channel until it did. In a live agent that is a process panic, not a lost event: it was observed in a test run immediately after "Self-destruct sequence completed", where the dispatcher outlives the shutdown that closed its channel. Use a two-value receive and return when the channel closes. A nil event is skipped rather than dereferenced. The regression test fails with a panic against the old code and passes against the new one, which was verified by reverting the fix and re-running it. Relates to #1326 Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
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Included review availability: Your plan provides up to 12 included reviews per hour; 11 remain after this review. 📝 WalkthroughWalkthroughThe NVCA event dispatcher now exits when its event channel closes and ignores nil events. Regression coverage verifies live Pod event processing, clean shutdown, and no additional queue entries. ChangesNVCA event dispatcher safety
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🔵 Low · up to The change prevents an NVCA agent shutdown panic, but the regression test may still pass if the dispatcher continues spinning after the event channel closes. The PR is mergeable with explicit owner awareness or follow-up to verify dispatcher termination deterministically. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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🧪 Generate unit tests (beta)
Warning Some tools did not complete. Review the errors below. 🔧 golangci-lint (2.12.2)level=error msg="Running error: context loading failed: failed to load packages: failed to load packages: failed to load with go/packages: err: exit status 1: stderr: go: inconsistent vendoring in /src/compute-plane-services/nvca:\n\tgithub.com/NVIDIA/KAI-scheduler@v0.12.6: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt\n\tgithub.com/NVIDIA/k8s-dra-driver-gpu@v0.0.0-20251017125642-cfe35ffd3d2c: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt\n\tgithub.com/NVIDIA/nvcf/src/libraries/go/lib@v0.0.0-20260722095202-f5e2792f5630: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt\n\tgithub.com/aws/aws-sdk-go@v1.55.5: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt\n\tgithub.com/bombsimon/logrusr/v4@v4.1.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt\n\tgithub.com/evanphx/json-patch/v5@v5.9.11: is explicitly required in ... [truncated 21721 characters] ... i: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tk8s.io/apiextensions-apiserver: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tk8s.io/apimachinery: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tk8s.io/client-go: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tk8s.io/component-base: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tsigs.k8s.io/controller-runtime: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\tgolang.org/x/crypto: is replaced in go.mod, but not marked as replaced in vendor/modules.txt\n\n\tTo ignore the vendor directory, use -mod=readonly or -mod=mod.\n\tTo sync the vendor directory, run:\n\t\tgo mod vendor\n" Comment |
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Actionable comments posted: 3
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Inline comments:
In `@src/compute-plane-services/nvca/pkg/nvca/agent_test.go`:
- Line 2721: Replace the fixed time.Sleep in the dispatcher test with a
deterministic completion signal from startEventProcessDispatchers or an
equivalent test hook. After close(events), wait for dispatcher termination using
that signal and a timeout, preserving the test’s failure behavior if termination
does not occur.
- Line 2713: Update the test around the events channel to send a nil event
before the non-nil Pod event while the channel remains open, then close it
afterward, covering both the nil-event and closed-channel paths.
In `@src/compute-plane-services/nvca/pkg/nvca/agent.go`:
- Line 798: Update the event dispatcher shutdown log near the “Event channel
closed” message to use a logger enriched with structured request, function,
cluster, and organization ID context before emitting the message. Ensure the
dispatcher no longer logs through the unchanged production logger for this
shutdown path.
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src/compute-plane-services/nvca/pkg/nvca/agent.gosrc/compute-plane-services/nvca/pkg/nvca/agent_test.go
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The dispatcher fix guards two cases, a closed channel and a nil event on an open one, but the test only exercised the closed channel. Sending a nil event first covers the other guard, and because the channel is unbuffered the following send only completes once the dispatcher has consumed it, so a regression blocks the test rather than passing quietly. Removing the guard makes this test panic again. The closed-channel assertion sampled the queue once after a fixed sleep. The failure it guards against is a dispatcher spinning on the closed channel and enqueueing continuously, so assert the queue never grows instead. Co-Authored-By: Balaji Ganesan <bganesan@nvidia.com>
2 participants
Why
Agent.startEventProcessDispatchersreceived events with a single-valuereceive. A closed channel yields the zero value immediately and forever, so
once the event channel closed the dispatcher dereferenced a nil
*core.Eventand panicked, and span on the closed channel until it did.
In a live agent this is a process panic, not a lost event. It surfaced in a
test run immediately after
Self-destruct sequence completed, where thedispatcher goroutine outlives the shutdown that closed its channel. It
presents as a rare, unrelated-looking test flake, which is how it went
unnoticed.
What changed
Two-value receive: return when the channel closes, skip a nil event rather
than dereferencing it. Twelve lines in
agent.go.Customer Release Notes
Fixed a rare NVCA agent crash during shutdown.
Plan Summary
Not applicable.
Usage
Not applicable.
Testing
TestEventDispatcherSurvivesClosedChannelasserts a live event still reachesits queue, then closes the channel and requires the dispatcher to stop
quietly.
The test was verified to catch the defect: with the fix reverted it panics the
test binary, and with the fix applied it passes.
go build ./...andgo test ./pkg/nvca/...are clean.QA: not required.
Notes
Found while chasing what looked like a flake in an unrelated storage change.
Split out here because it is independent of that work and worth merging on its
own.
Issues
Closes #1431
Related Pull Requests
None
Dependencies
None
Summary by CodeRabbit
Bug Fixes
Tests