fix: implement atomic DataSource adapter update to prevent torn reads - #181
fix: implement atomic DataSource adapter update to prevent torn reads#181peatey wants to merge 1 commit into
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- Add adapterState struct to group all four adapter components - Replace individual adapter fields with atomic.Pointer[adapterState] - Update all accessor methods to use atomic Load() - Modify Update() to swap complete state atomically - Add comprehensive race condition tests - All tests pass with go test -race (zero data races) This ensures readers always see a fully consistent set of adapters (either all old or all new, never mixed) without any mutex contention.
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Pull request overview
This PR aims to prevent “torn reads” by grouping the OpenCost data source’s adapter components into a single state object and swapping that state atomically so readers observe a consistent set of adapters during updates.
Changes:
- Introduces an
adapterStatecontainer and replaces individual adapter fields withatomic.Pointer[adapterState]. - Updates accessor methods (
Metrics,ClusterMap,ClusterInfo,ClusterCache) to read adapters viastate.Load(). - Adds new concurrency-focused tests intended to validate race-safety and read consistency.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.
| File | Description |
|---|---|
kubecost/adapters/datasource.go |
Refactors the data source adapter to use an atomically-swapped state wrapper and updates accessors accordingly. |
kubecost/adapters/datasource_test.go |
Adds tests for concurrent update/read behavior and basic post-update consistency checks. |
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| Window: opencost.NewClosedWindow( | ||
| time.Now().Truncate(10*time.Minute), | ||
| time.Now().Truncate(10*time.Minute).Add(10*time.Minute), | ||
| ), |
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The window bounds are built from two separate time.Now() calls. If the calls straddle a 10-minute boundary, start and end may not represent a single 10m window, making the test flaky. Capture now := time.Now().Truncate(10*time.Minute) once and derive both start/end from it.
| // Read all four accessors in sequence | ||
| // If there's a torn read, the race detector will catch it | ||
| _ = adapter.Metrics() | ||
| _ = adapter.ClusterMap() | ||
| _ = adapter.ClusterInfo() | ||
| _ = adapter.ClusterCache() | ||
| } |
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The comment says “If there's a torn read, the race detector will catch it”, but -race only detects unsynchronized concurrent memory access, not logical consistency/torn-read conditions. If the intent is to validate consistency, add explicit assertions (e.g., read a single state handle and verify fields correspond to the same snapshot) instead of relying on the race detector.
| go func(id int) { | ||
| defer wg.Done() | ||
| for j := 0; j < 1000; j++ { |
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The reader goroutine takes an id parameter but never uses it. Consider removing the parameter (or using it for debugging/logging) to avoid dead code and keep the test minimal.
| func (ocdsa *OpenCostDataSourceAdapter) Update(snapshot *emitter.ClusterSnapshot) { | ||
| ocdsa.infoAdapter.Update(snapshot.ClusterInfo) | ||
| ocdsa.mapAdapter.Update(snapshot.ClusterInfo) | ||
| ocdsa.clusterAdapter.Update(snapshot.Kubernetes) | ||
| ocdsa.metricsAdapter.Update(snapshot.Metrics) | ||
| // Load current state to get the existing adapters | ||
| current := ocdsa.state.Load() | ||
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| // Update each adapter (these modify internal state via their own locks) | ||
| current.info.Update(snapshot.ClusterInfo) | ||
| current.mapAdpt.Update(snapshot.ClusterInfo) | ||
| current.cluster.Update(snapshot.Kubernetes) | ||
| current.metrics.Update(snapshot.Metrics) | ||
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| // Build a new state object with the updated adapters and swap it in. | ||
| // After this single Store() call, all readers see the new state atomically. | ||
| newState := &adapterState{ | ||
| info: current.info, | ||
| mapAdpt: current.mapAdpt, | ||
| cluster: current.cluster, | ||
| metrics: current.metrics, | ||
| } | ||
| ocdsa.state.Store(newState) |
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Update mutates the adapters in-place (info/map/cluster/metrics) and then stores a new adapterState that points to the exact same adapter instances. This does not achieve the stated goal of “either all old or all new”: readers can still observe partially-updated adapter contents while Update is in progress, and the final Store is effectively a no-op. If atomic consistency across all four adapters is required, build a fresh set of adapters from snapshot (or an immutable snapshot wrapper) and Store that state without mutating the previously-published adapters; otherwise, keep the simpler non-atomic fields and remove the misleading atomic swap.
| // adapterState groups all adapter components so they can be swapped atomically. | ||
| // This ensures readers always get a fully consistent set of adapters — either all old or all new, never mixed. | ||
| type adapterState struct { |
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The comment claims readers get “a fully consistent set of adapters — either all old or all new”, but each accessor does its own state.Load() and Update currently mutates adapters in-place. At best this prevents mixed pointers if state were swapped, but it doesn’t guarantee a consistent multi-accessor view. Consider tightening the doc comment to the actual guarantee, or provide an API that returns a single loaded state handle for callers that need cross-accessor consistency.
| type adapterState struct { | ||
| info *ClusterInfoProviderAdapter | ||
| mapAdpt *ClusterMapAdapter | ||
| cluster *ClusterCacheAdapter | ||
| metrics *MetricsQuerierAdapter |
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mapAdpt is a hard-to-scan abbreviation and inconsistent with the constructor parameter mapAdapter. Consider renaming it to something clearer like mapAdapter or clusterMap to avoid confusion.
| ClusterInfo: &clusters.ClusterInfo{ | ||
| ID: "test-cluster-" + string(rune(i)), | ||
| Name: "test-cluster", | ||
| Provider: "test-provider", | ||
| }, |
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"test-cluster-" + string(rune(i)) does not append the decimal representation of i; it converts i to a single Unicode code point (including control characters for small values). Use strconv.Itoa(i)/fmt.Sprintf("%d", i) to generate deterministic IDs.
This ensures readers always see a fully consistent set of adapters (either all old or all new, never mixed) without any mutex contention.