go runtime_error ai_generated true

fatal error: concurrent map iteration and map write

ID: go/concurrent-map-write-during-range

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-02-27First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.18 active — — —
1.21 active — — —
1.22 active — — —

Root Cause

A map is being range-iterated in one goroutine while another goroutine writes to the same map, violating Go's map safety rules.

generic

中文

一个 goroutine 正在 range 遍历 map，同时另一个 goroutine 写入同一个 map，违反了 Go 的 map 安全规则。

Workarounds

  1. 97% success 
    var mu sync.RWMutex
mu.RLock()
for k, v := range m { _ = k; _ = v }
mu.RUnlock()
// writer:
mu.Lock()
m[k] = v
mu.Unlock()
  2. 90% success 
    var m sync.Map
m.Range(func(k, v any) bool { return true })
m.Store(key, val)

Dead Ends

Common approaches that don't work:

  1. 90% fail

    Timing-based avoidance is unreliable; the runtime can still detect concurrent access under load.

  2. 95% fail

    This is a fatal runtime error, not a panic; recover cannot catch it and the process exits.