go runtime_error ai_generated true

error: select on nil channel blocks forever

ID: go/nil-channel-blocks-forever

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-09-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0 active — — —
1.21 active — — —
1.22 active — — —

Root Cause

Sending to or receiving from a nil channel blocks forever. In a select, a nil channel case is never ready, so if all cases are nil, the select blocks indefinitely.

generic

中文

向 nil 通道发送或从 nil 通道接收会永久阻塞。在 select 中，nil 通道分支永远不会就绪，若所有分支都是 nil，select 会无限阻塞。

Workarounds

  1. 95% success 
    var ch chan int = make(chan int)
select {
case v := <-ch: _ = v
case <-time.After(time.Second):
}
  2. 85% success 
    var never chan struct{} // nil disables the case
select {
case <-never:
case <-ch:
}

Dead Ends

Common approaches that don't work:

  1. 85% fail

    With default, the select always takes the default branch, so nothing ever happens; the intended wait is lost.

  2. 75% fail

    The outer select still holds the nil reference; the goroutine's new channel is unrelated.