go runtime_error ai_generated true

fatal error: concurrent map iteration and map write

ID: go/fatal-error-concurrent-map-iteration-and-map-write

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-06-18First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.18 active — — —
1.22 active — — —

Root Cause

One goroutine ranges over a map while another goroutine writes to it, which the runtime detects and aborts.

generic

中文

一个 goroutine 正在 range 遍历 map，同时另一个 goroutine 写入该 map，运行时检测到并中止。

Workarounds

  1. 92% success 
    Hold a sync.RWMutex: mu.RLock(); for k, v := range m { ... }; mu.RUnlock(), and mu.Lock() for writes.
  2. 90% success 
    Snapshot under lock: mu.RLock(); snapshot := make(map[K]V, len(m)); for k, v := range m { snapshot[k] = v }; mu.RUnlock(); then range over snapshot.

Dead Ends

Common approaches that don't work:

  1. 85% fail

    The copy itself races with the writer; the runtime aborts during the copy loop.

  2. 90% fail

    Maps have no index operator; this does not compile, and even an equivalent iteration still races.