go runtime_error ai_generated true

fatal error: concurrent map iteration and map write

ID: go/racy-map-access

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-10-05First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.6 active — — —
1.21 active — — —

Root Cause

One goroutine is iterating over a map while another goroutine writes to it, causing a race condition.

generic

中文

一个 goroutine 正在迭代 map，而另一个 goroutine 正在写入该 map，导致竞态条件。

Workarounds

  1. 95% success Use sync.RWMutex to protect both reads and writes 
    var mu sync.RWMutex
mu.RLock()
for k, v := range myMap { ... }
mu.RUnlock()
mu.Lock()
myMap[key] = value
mu.Unlock()
  2. 90% success Use sync.Map for concurrent-safe map operations 
    var m sync.Map
m.Store(key, value)
m.Load(key)

Dead Ends

Common approaches that don't work:

  1. Using a sync.Mutex only around writes 85% fail

    Iteration also needs protection; concurrent iteration and write still race.

  2. Using a RWMutex for reads but not for iteration 80% fail

    Iteration is a read operation but may still race with writes if not locked.