go runtime_error ai_generated true

fatal error: all goroutines are asleep - deadlock! (select with nil channels)

ID: go/select-on-nil-channels

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-05-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0 active — — —
1.1 active — — —

Root Cause

A select statement with multiple cases where all channels are nil. In Go, a select with all nil channels blocks forever because no case can proceed.

generic

中文

一个选择语句有多个 case，但所有通道都是 nil。在 Go 中，所有通道都是 nil 的选择会永远阻塞，因为没有 case 可以执行。

Workarounds

  1. 95% success Ensure all channels in select are non-nil 
    ch1 := make(chan int)
ch2 := make(chan int)
select {
case <-ch1:
case <-ch2:
}
  2. 90% success Use a helper function to filter out nil channels 
    func nonNilChannels(chs ...chan int) []chan int {
    var result []chan int
    for _, ch := range chs {
        if ch != nil {
            result = append(result, ch)
        }
    }
    return result
}

Dead Ends

Common approaches that don't work:

  1. Adding a default case to the select 80% fail

    A default case will execute immediately if all channels are nil, but it doesn't solve the underlying issue of nil channels; it just avoids the block.

  2. Removing the select and using direct channel operations 95% fail

    Direct operations on nil channels will also block forever, so this doesn't help.