go runtime_error ai_generated true

panic: close of closed channel (in for range)

ID: go/goroutine-for-range-channel-close

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-12-08First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.20 active — — —
1.21 active — — —

Root Cause

Closing a channel that is being ranged over by another goroutine, causing a panic when the range attempts to read from the closed channel.

generic

中文

关闭正在被另一个协程 range 的通道，导致 range 尝试从已关闭通道读取时引发恐慌。

Workarounds

  1. 100% success Use a separate goroutine to close the channel after all sends are done. 
    ch := make(chan int)
go func() {
    for i := 0; i < 10; i++ {
        ch <- i
    }
    close(ch)
}()
for v := range ch {
    fmt.Println(v)
}
  2. 95% success Use a sync.WaitGroup to coordinate closure. 
    var wg sync.WaitGroup
wg.Add(1)
go func() {
    defer wg.Done()
    for i := 0; i < 10; i++ {
        ch <- i
    }
}()
go func() {
    wg.Wait()
    close(ch)
}()
for v := range ch {
    fmt.Println(v)
}

Dead Ends

Common approaches that don't work:

  1. Closing the channel inside the range loop. 80% fail

    Range loop continues until channel is closed, but closing inside causes panic on next iteration.

  2. Using a defer close in the sender goroutine that ranges. 70% fail

    If the sender is also the range receiver, closing inside the loop is problematic.