go runtime_error ai_generated true

fatal error: all goroutines are asleep - deadlock! (unbuffered channel)

ID: go/unbuffered-channel-blocking

Also available as: JSON · Markdown · 中文
80%Fix Rate
86%Confidence
0Evidence
2024-09-05First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.20 active — — —
1.21 active — — —
1.22 active — — —

Root Cause

An unbuffered channel requires both sender and receiver to be ready simultaneously. If only one side is ready, it blocks indefinitely.

generic

中文

无缓冲通道要求发送方和接收方同时就绪。如果只有一方就绪，就会无限期阻塞。

Workarounds

  1. 90% success Ensure both sender and receiver are started before the blocking operation 
    ch := make(chan int)

go func() {
    val := <-ch
    fmt.Println(val)
}()

ch <- 42 // now this won't block because receiver is ready
  2. 80% success Use a buffered channel with a reasonable capacity 
    ch := make(chan int, 10) // buffer size 10

Dead Ends

Common approaches that don't work:

  1. Making the channel buffered with a small size 50% fail

    A small buffer may not be sufficient; if the buffer fills up, the same deadlock can occur.

  2. Using time.Sleep to give the other side time to prepare 75% fail

    Sleeping is non-deterministic and doesn't guarantee both sides are ready; it may still deadlock.