go runtime_error ai_generated true

fatal error: concurrent slice append

ID: go/goroutine-racy-slice-append

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

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0 active — — —
1.21 active — — —

Root Cause

Multiple goroutines appending to the same slice without synchronization, causing data race.

generic

中文

多个协程向同一个slice追加元素而没有同步，导致数据竞争。

Workarounds

  1. 90% success Use mutex to protect slice append 
    var mu sync.Mutex
var s []int
mu.Lock()
s = append(s, 1)
mu.Unlock()
  2. 85% success Use channel to collect results 
    ch := make(chan int, 10)
for i := 0; i < 10; i++ {
    go func(val int) {
        ch <- val
    }(i)
}
var s []int
for i := 0; i < 10; i++ {
    s = append(s, <-ch)
}

Dead Ends

Common approaches that don't work:

  1. Pre-allocating slice with make to avoid reallocation 80% fail

    Append still modifies slice header; concurrent writes race on length.

  2. Using copy-on-write pattern manually 70% fail

    Complex and error-prone; still racy without synchronization.