go runtime_error ai_generated true

fatal error: concurrent map iteration and map write

ID: go/concurrent-map-iterations

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-06-09First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0+ active — — —

Root Cause

A goroutine iterates a map with for range while another goroutine writes to the same map, which the runtime detects and aborts.

generic

中文

某 goroutine 使用 for range 迭代 map，同时另一 goroutine 向同一 map 写入，运行时检测到后直接终止。

Workarounds

  1. 97% success 
    mu.Lock()
for k, v := range m { process(k, v) }
mu.Unlock()
  2. 93% success 
    type req struct{ reply chan map[string]int }
for r := range reqs { r.reply <- snapshot(m) }

Dead Ends

Common approaches that don't work:

  1. 88% fail

    Copying without locking still races with the writer during the copy itself.

  2. 86% fail

    Taking the snapshot races with concurrent writes and can still trigger the detector.