当非阻塞读取行挂起时，goroutine泄漏

Question

Assuming you have a structure like this:

ch := make(chan string)
errCh := make(chan error)
go func() {
    line, _, err := bufio.NewReader(r).ReadLine()
    if err != nil {
        errCh <- err
    } else {
        ch <- string(line)
    }
}()
select {
case err := <-errCh:
    return "", err
case line := <-ch:
    return line, nil
case <-time.After(5 * time.Second):
    return "", TimeoutError
}

In the case of the 5 second timeout, the goroutine hangs until ReadLine returns, which may never happen. My project is a long-running server, so I don't want a buildup of stuck goroutines.

Answer 1

ReadLine will not return until either the process exits or the method reads a line. There's no deadline or timeout mechanism for pipes.

The goroutine will block if the call to ReadLine returns after the timeout. This can be fixed by using buffered channels:

ch := make(chan string, 1)
errCh := make(chan error, 1)

The application should call Wait to cleanup resources associated with the command. The goroutine is a good place to call it:

go func() {
  line, _, err := bufio.NewReader(r).ReadLine()
  if err != nil {
    errCh <- err
  } else {
    ch <- string(line)
  }
  cmd.Wait() // <-- add this line
}()

This will cause the goroutine to block, the very thing you are trying to avoid. The alternative is that the application leaks resources for each command.