go runtime_error ai_generated true

panic: receive from closed channel (in range)

ID: go/goroutine-range-over-closed-channel

Also available as: JSON · Markdown · 中文
80%Fix Rate
84%Confidence
0Evidence
2024-06-18First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0 active — — —
1.20 active — — —

Root Cause

Iterating over a channel with range after it has been closed; range receives zero values until channel is drained.

generic

中文

在通道关闭后使用range迭代；range会接收零值直到通道耗尽。

Workarounds

  1. 95% success Use for with ok pattern instead of range 
    for {
    val, ok := <-ch
    if !ok {
        break
    }
    // process val
}
  2. 90% success Ensure channel is closed only after all sends are done 
    var wg sync.WaitGroup
for i := 0; i < 5; i++ {
    wg.Add(1)
    go func() {
        defer wg.Done()
        ch <- i
    }()
}
wg.Wait()
close(ch)
for val := range ch {
    // process
}

Dead Ends

Common approaches that don't work:

  1. Using recover() to catch panic from zero value 90% fail

    Range over closed channel doesn't panic; it returns zero values, which may cause logic errors.

  2. Checking channel length before range 80% fail

    len(ch) doesn't indicate closed state; closed channel can have buffered data.