go runtime_error ai_generated true

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

ID: go/goroutine-waitgroup-wait-in-loop

Also available as: JSON · Markdown · 中文
80%Fix Rate
84%Confidence
0Evidence
2024-12-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0 active — — —
1.20 active — — —

Root Cause

Calling Add() on a WaitGroup while a previous Wait() is still in progress, causing race.

generic

中文

在之前的Wait()仍在进行时对WaitGroup调用Add()，导致竞态条件。

Workarounds

  1. 95% success Create a new WaitGroup for each batch 
    for batch := 0; batch < 3; batch++ {
    var wg sync.WaitGroup
    for i := 0; i < 5; i++ {
        wg.Add(1)
        go func() { defer wg.Done(); /* work */ }()
    }
    wg.Wait()
}
  2. 85% success Use channels to synchronize instead of reusing WaitGroup 
    ch := make(chan struct{})
for i := 0; i < 5; i++ {
    go func() { /* work */; ch <- struct{}{} }()
}
for i := 0; i < 5; i++ {
    <-ch
}

Dead Ends

Common approaches that don't work:

  1. Using recover() to catch panic 100% fail

    Panic is unrecoverable in this context; program crashes.

  2. Adding more Done() calls to unblock Wait 90% fail

    Counter imbalance causes negative counter panic.