Cancelling golang os.Stdin read using context - linux

Question

I want to be able to cancel an os.Stdin read using context which is not possible. Usually, you close the file handle to accomplish cancel, but I do not want to close os.Stdin
Possible solutions could be:
Can it be determined if Stdin.Read will block?
Can the thread be terminated like in pthreads?
Should os.Stdin be forwarded to another file handle that can be closed?
Here’s what I got, the ugliness is that scannerThread is left running on context cancelation:
// Keystrokes emits keystroke events
// on g0.Context() shutdown, scannerThread is left running until the next newline
// the lines channel is never closed
func Keystrokes(lines chan<- string, g0 parl.Go) {
var err error
defer g0.Done(err)
defer parl.Recover(parl.Annotation(), &err, parl.NoOnError)
// stdio.Scan cannot be terminated, so let that thread terminate whenever
var scanLines parl.NBChan[string]
go scannerThread(scanLines.Send, g0.Context())
// consume scannerThread output
scannerCh := scanLines.Ch()
done := g0.Context().Done()
for {
select {
case line := <-scannerCh:
lines <- line
case <-done:
return // canceled by context exit
}
}
}
// scannerThread reads from os.Stdin and therefore cannot be cancelled.
// send is a non-blocking send function.
// ctx indicates shutdown effective on next os.Stdin newline.
func scannerThread(send func(string), ctx context.Context) {
var err error
defer parl.Recover(parl.Annotation(), &err, parl.Infallible)
scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() { // scanner is typically stuck here
if ctx.Err() != nil {
return // terminated via context
}
send(scanner.Text())
}
// scanner had error
err = scanner.Err()
}

Answer 1

The answer is to read os.Stdin non-blocking, works on Linux macOS
os.Stdin has a block against closing it, I remember
Non-blocking os.Stdin.Read() returns bytes once a complete line is available, otherwise returns n==0
Here is how to set non-blocking:
err = unix.SetNonblock(int(os.Stdin.Fd()), true)
The state of non-blocking can also be read:
flags, err := unix.FcntlInt(os.Stdin.Fd(), unix.F_GETFL, 0)
wasSet = flags&unix.O_NONBLOCK != 0