go runtime_error ai_generated true

fatal error: concurrent map read and map write

ID: go/goroutine-map-concurrent-read-and-write

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-10-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.18 active — — —
1.19 active — — —
1.20 active — — —
1.21 active — — —

Root Cause

One goroutine reads from a map while another writes to it without synchronization, causing a data race.

generic

中文

一个协程从 map 中读取，而另一个协程在没有同步的情况下写入 map，导致数据竞争。

Workarounds

  1. 95% success Use sync.RWMutex to protect both reads and writes 
    var mu sync.RWMutex
mu.RLock()
val := myMap[key]
mu.RUnlock()
  2. 90% success Use sync.Map for concurrent read/write 
    var m sync.Map
m.Load(key) // safe concurrent read

Dead Ends

Common approaches that don't work:

  1. Use a read-write lock (sync.RWMutex) only for writes 60% fail

    If reads are not protected, they can still race with writes.

  2. Use a copy of the map for reads 90% fail

    Copying a map while it is being written is unsafe and can cause a race.