go runtime_error ai_generated true

panic: sync: WaitGroup is reused before previous Wait has returned

ID: go/waitgroup-misused-copy

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-05-21First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.20 active — — —
1.23 active — — —

Root Cause

wg.Add called again while another goroutine is still in wg.Wait. Typically happens with a loop that reuses the same WaitGroup across iterations without resetting.

generic

中文

在另一个 goroutine 仍处于 wg.Wait 时再次调用 wg.Add。通常发生在循环中跨迭代复用同一个 WaitGroup 而未重置。

Workarounds

  1. 95% success 
    for _, batch := range batches {
    var wg sync.WaitGroup
    for _, x := range batch {
        wg.Add(1)
        go func(x int) { defer wg.Done(); work(x) }(x)
    }
    wg.Wait()
}
  2. 93% success 
    for _, batch := range batches {
    g := new(errgroup.Group)
    for _, x := range batch { x := x; g.Go(func() error { return work(x) }) }
    if err := g.Wait(); err != nil { return err }
}

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Reassigning while Wait is in flight races on the struct; still panics or corrupts state.

  2. 80% fail

    Sleep does not synchronize with Wait's completion; race remains.