go runtime_error ai_generated true

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

ID: go/waitgroup-wait-reused-before-return

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-04-18First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.20 active — — —
1.21 active — — —
1.22 active — — —

Root Cause

Add() is called on a WaitGroup while another goroutine is still blocked in Wait(), which the runtime forbids to prevent counter races.

generic

中文

在另一个 goroutine 仍阻塞在 Wait() 时调用了 Add()，运行时会禁止此操作以防止计数器竞争。

Workarounds

  1. 95% success 
    var wg sync.WaitGroup
for i := 0; i < n; i++ { wg.Add(1) }
for i := 0; i < n; i++ {
    go func() { defer wg.Done(); work() }()
}
wg.Wait()
  2. 93% success 
    sem := make(chan struct{}, 10)
var wg sync.WaitGroup
for _, job := range jobs {
    sem <- struct{}{}
    wg.Add(1)
    go func(j Job) {
        defer wg.Done()
        defer func() { <-sem }()
        run(j)
    }(job)
}
wg.Wait()

Dead Ends

Common approaches that don't work:

  1. 80% fail

    Wait() may return before the goroutine even starts, so Add happens after Wait and the counter update races.

  2. 70% fail

    Sleep does not synchronize Add with Wait; under load the panic still occurs.