go runtime_error ai_generated true

panic: runtime error: index out of range [0] with length 0 (in goroutine)

ID: go/goroutine-slice-concurrent-access

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2025-01-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.21 active — — —
1.22 active — — —

Root Cause

Multiple goroutines append to a slice without synchronization, causing the slice to be corrupted or accessed incorrectly.

generic

中文

多个协程在没有同步的情况下向切片追加元素，导致切片损坏或访问不正确。

Workarounds

  1. 98% success Use sync.Mutex to protect slice append 
    var mu sync.Mutex
var s []int
for i := 0; i < 10; i++ {
    go func(val int) {
        mu.Lock()
        s = append(s, val)
        mu.Unlock()
    }(i)
}
  2. 95% success Use a 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 capacity 80% fail

    Pre-allocation does not prevent concurrent append races; the length field is still modified concurrently.

  2. Using a local slice per goroutine and merging later 70% fail

    Merging slices concurrently can still cause races if not synchronized.