go runtime_error ai_generated true

fatal error: concurrent map iteration and map write

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

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-06-03First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0+ active — — —

Root Cause

A goroutine iterates a map with range while another goroutine writes to it, which the runtime flags as a fatal race.

generic

中文

一个 goroutine 用 range 遍历 map，同时另一个 goroutine 写入该 map，运行时将其视为致命竞争。

Workarounds

  1. 93% success 
    Hold an RWMutex read lock for the whole iteration and use a write lock for mutations.
  2. 88% success 
    Snapshot the map under a lock into a plain slice, then iterate the slice outside the lock.

Dead Ends

Common approaches that don't work:

  1. 70% fail

    The write still races with the copy loop and can panic during the copy itself.