go runtime_error ai_generated true

panic: send on closed channel

ID: go/channel-send-on-closed

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-03-11First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.0+ active — — —

Root Cause

A goroutine calls ch <- v after another goroutine has already called close(ch). Go panics immediately because sending to a closed channel is always a programming error, unlike receiving which returns the zero value.

generic

中文

某个 goroutine 在另一个 goroutine 已调用 close(ch) 之后执行 ch <- v。Go 会立即 panic，因为向已关闭 channel 发送永远是编程错误，而接收则会返回零值。

Workarounds

  1. 92% success 
    Make the sender the only owner of close. Use a done channel and select so senders never write after shutdown:
select {
case ch <- v:
case <-done:
    return
}
  2. 80% success 
    Use sync.Once for close and guard sends with a mutex + closed flag:
mu.Lock()
if !closed { ch <- v }
mu.Unlock()

Dead Ends

Common approaches that don't work:

  1. 90% fail

    recover() only works in the same goroutine that is panicking, and even then it hides the race; the underlying close/send race remains and data is silently lost.

  2. 85% fail

    select default does not protect against a closed channel; a send case on a closed channel still panics when selected.