go runtime_error ai_generated true

fatal error: concurrent map read and map write

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

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-12-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.21 active — — —
1.22 active — — —

Root Cause

One goroutine reads from a map while another goroutine writes to it without synchronization.

generic

中文

一个协程读取map时，另一个协程在无同步的情况下写入该map。

Workarounds

  1. 97% success Use sync.RWMutex for read-write protection 
    var mu sync.RWMutex
m := make(map[string]int)
// write
mu.Lock()
m["key"] = 1
mu.Unlock()
// read
mu.RLock()
val := m["key"]
mu.RUnlock()
  2. 95% success Use a single goroutine to own the map and communicate via channels 
    ch := make(chan request)
go func() {
    m := make(map[string]int)
    for req := range ch {
        switch req.op {
        case "read":
            req.resp <- m[req.key]
        case "write":
            m[req.key] = req.val
        }
    }
}()

Dead Ends

Common approaches that don't work:

  1. Using a read-only copy of the map 75% fail

    Copying a map during concurrent writes is also racy.

  2. Using a channel to serialize access 60% fail

    If not done correctly, it can introduce deadlocks.