go runtime_error ai_generated true

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

ID: go/goroutine-unbuffered-channel-blocking

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
0Evidence
2024-09-18First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.20 active — — —
1.21 active — — —

Root Cause

An unbuffered channel send blocks until a receiver is ready; if no receiver exists, the goroutine deadlocks.

generic

中文

无缓冲通道发送会阻塞直到有接收者就绪；如果没有接收者，协程会死锁。

Workarounds

  1. 95% success Use a buffered channel to allow sends without immediate receiver. 
    ch := make(chan int, 1)
ch <- 42 // non-blocking
val := <-ch
fmt.Println(val)
  2. 100% success Ensure a receiver goroutine is started before sending. 
    ch := make(chan int)
go func() {
    val := <-ch
    fmt.Println(val)
}()
ch <- 42 // now receiver is ready

Dead Ends

Common approaches that don't work:

  1. Using a buffered channel but with size 0, which is unbuffered. 90% fail

    make(chan int, 0) creates an unbuffered channel, still blocking.

  2. Adding a receiver in the same goroutine after the send. 100% fail

    The send blocks before the receiver is reached, causing deadlock.