go runtime_error ai_generated true

fatal error: all goroutines are asleep - deadlock! (select with no ready case)

ID: go/select-no-default-blocks

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-05-22First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.17 active — — —
1.21 active — — —
1.22 active — — —

Root Cause

A select statement with no default blocks until one case becomes ready. If no channel ever becomes ready, the program deadlocks.

generic

中文

没有 default 的 select 语句会阻塞直到某个 case 就绪。如果没有任何 channel 就绪，程序死锁。

Workarounds

  1. 95% success 
    select {
case v := <-ch:
    use(v)
case <-time.After(5 * time.Second):
    return errTimeout
}
  2. 96% success 
    select {
case v := <-ch:
    use(v)
case <-ctx.Done():
    return ctx.Err()
}

Dead Ends

Common approaches that don't work:

  1. 70% fail

    The select now spins in a busy loop consuming CPU without ever making progress.

  2. 80% fail

    Creates a livelock if no case is ever ready; the program hangs forever.