fix: eliminate sync.Once reset data race in cache-clear functions by Copilot · Pull Request #18280 · github/gh-aw

Copilot · 2026-02-25T06:28:23Z

Resetting sync.Once via = sync.Once{} is a data race under the Go memory model when any goroutine is concurrently inside Do() or reading the once's internal state. Two cache-clear functions in pkg/cli/repo.go and pkg/workflow/repository_features_validation.go had this pattern.

Changes

pkg/cli/repo.go — replaced sync.Once + bare result/error vars with a mutex-guarded repoSlugCacheState struct; ClearCurrentRepoSlugCache() now locks and zeroes fields individually
pkg/workflow/repository_features_validation.go — same pattern: replaced sync.Once + bare vars with currentRepositoryCacheState; ClearRepositoryFeaturesCache() uses the same mutex-protected reset

// Before — data race: writing sync.Once{} while Do() may be running
func ClearCurrentRepoSlugCache() {
    getCurrentRepoSlugOnce = sync.Once{}
    currentRepoSlugResult  = ""
    currentRepoSlugError   = nil
}

// After — mutex-guarded struct, safe to call concurrently with reads
type repoSlugCacheState struct {
    mu     sync.Mutex
    result string
    err    error
    done   bool
}

func ClearCurrentRepoSlugCache() {
    currentRepoSlugCache.mu.Lock()
    defer currentRepoSlugCache.mu.Unlock()
    currentRepoSlugCache.result = ""
    currentRepoSlugCache.err    = nil
    currentRepoSlugCache.done   = false
}

The read path (GetCurrentRepoSlug / getCurrentRepository) mirrors the pattern: lock → check done → compute if needed → copy results → unlock.

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Original prompt

This section details on the original issue you should resolve

<issue_title>[plan] Fix sync.Once reset data race in cache-clear functions</issue_title>
<issue_description>## Objective

Fix a data race caused by resetting sync.Once values via direct struct assignment (= sync.Once{}), which violates the Go memory model.

Context

From Sergo analysis run §22372431560 (discussion #18227).

Two cache-clear functions reset sync.Once by writing = sync.Once{}, which is a data race per the Go memory model if any goroutine is concurrently inside Do() or reading the once's internal state. The companion result/error variables are also unsynchronized.

Go's sync package documentation states: "A Once must not be copied after first use."

Affected Locations

File Line Code

pkg/cli/repo.go ~26 getCurrentRepoSlugOnce = sync.Once{}

pkg/workflow/repository_features_validation.go ~88 getCurrentRepositoryOnce = sync.Once{}

Approach

Replace the sync.Once reset pattern with a safe alternative:

Option A – Use a sync.Mutex-guarded reset function:
var mu sync.Mutex
var once sync.Once
var cachedResult string
var cachedErr error

func clearCache() {
    mu.Lock()
    defer mu.Unlock()
    once = sync.Once{} // Still racy — don't do this
}
Option B (Recommended) – Replace with an atomic pointer or a mutex-protected struct:
type cacheState struct {
    result string
    err    error
    done   bool
}
var mu sync.Mutex
var state cacheState

func getOrCompute() (string, error) {
    mu.Lock()
    defer mu.Unlock()
    if !state.done {
        state.result, state.err = compute()
        state.done = true
    }
    return state.result, state.err
}

func clearCache() {
    mu.Lock()
    defer mu.Unlock()
    state = cacheState{}
}
Option C – Use atomic.Pointer with a copy-on-write approach if performance is critical.

Pick the simplest option that eliminates the race while maintaining test utility (i.e., the clear function still works in tests).

Files to Modify

pkg/cli/repo.go

pkg/workflow/repository_features_validation.go

Corresponding test files if they exercise the clear functions

Acceptance Criteria

No direct sync.Once{} struct assignment after first use

Cache-clear functions are safe to call concurrently with cache-read functions

go test -race ./pkg/cli/... ./pkg/workflow/... passes without data race reports

Existing tests continue to pass

Generated by Plan Command for issue #discussion #18227

expires on Feb 27, 2026, 6:22 AM UTC

Comments on the Issue (you are @copilot in this section)
@pelikhan option B

Fixes [plan] Fix sync.Once reset data race in cache-clear functions #18277

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

…ata race Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot

Pull request overview

Eliminates a Go data race caused by resetting sync.Once via struct assignment in cache-clear functions by replacing sync.Once-based caching with a mutex-guarded cache state.

Changes:

Replaced sync.Once + separate result/error globals with a mutex-protected cache state struct for current repo slug caching.
Applied the same mutex-guarded cache state pattern to the current repository cache used by repository feature validation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/cli/repo.go	Reworks current repo slug caching to a mutex-guarded state (`done/result/err`) so cache clears are concurrency-safe.
pkg/workflow/repository_features_validation.go	Reworks current repository caching to a mutex-guarded state, avoiding unsafe `sync.Once` resets during cache clears.

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Initial plan

96c445e

Copilot AI assigned Copilot and pelikhan Feb 25, 2026

Copilot started work on behalf of pelikhan February 25, 2026 06:28 View session

fix: replace sync.Once reset with mutex-guarded struct to eliminate d…

938031c

…ata race Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix data race from resetting sync.Once in cache-clear functions~~ fix: eliminate sync.Once reset data race in cache-clear functions Feb 25, 2026

Copilot finished work on behalf of pelikhan February 25, 2026 06:38

pelikhan marked this pull request as ready for review February 25, 2026 06:50

Copilot AI review requested due to automatic review settings February 25, 2026 06:50

Copilot started reviewing on behalf of pelikhan February 25, 2026 06:51 View session

Copilot AI reviewed Feb 25, 2026

View reviewed changes

pelikhan merged commit 974efc0 into main Feb 25, 2026
110 checks passed

pelikhan deleted the copilot/fix-sync-once-data-race branch February 25, 2026 06:55

This was referenced Feb 25, 2026

[Daily Report] Daily Status Report — 2026-02-25 #18296

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fix: eliminate sync.Once reset data race in cache-clear functions#18280

fix: eliminate sync.Once reset data race in cache-clear functions#18280
pelikhan merged 2 commits intomainfrom
copilot/fix-sync-once-data-race

Copilot AI commented Feb 25, 2026 •

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File	Line	Code
`pkg/cli/repo.go`	~26	`getCurrentRepoSlugOnce = sync.Once{}`
`pkg/workflow/repository_features_validation.go`	~88	`getCurrentRepositoryOnce = sync.Once{}`

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Copilot AI commented Feb 25, 2026 •

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