go runtime_error ai_generated true

panic: sync: negative WaitGroup counter

ID: go/negative-waitgroup-counter

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-04-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.x active — — —

Root Cause

wg.Done() is called more times than wg.Add(n). Common when Done is deferred in a loop that runs more iterations than Add, or a goroutine calls Done without a matching Add.

generic

中文

wg.Done() 调用次数多于 wg.Add(n)。常见于在迭代次数多于 Add 的循环中 defer Done，或有 goroutine 调用 Done 却没有匹配的 Add。

Workarounds

  1. 95% success 
    Call Add(1) synchronously before launching each goroutine and defer Done inside:
for _, item := range items {
    wg.Add(1)
    go func(it Item){ defer wg.Done(); process(it) }(item)
}
wg.Wait()
  2. 92% success 
    Use golang.org/x/sync/errgroup which manages the counter correctly:
g, ctx := errgroup.WithContext(ctx)
for _, it := range items { it := it; g.Go(func() error { return process(ctx, it) }) }
return g.Wait()

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Race: Wait() may return before the goroutine has called Add, causing Done to decrement below zero or the wait to miss the goroutine.

  2. 80% fail

    The counter is already corrupted; recover leaves the WaitGroup in an invalid state.