On Sun, Jan 19, 2014 at 11:10 AM, Christopher Wellons <
well...@nullprogram.com> wrote:
>
> When the shell is set to interactive (i.e. "-interactive"), the output
> (stdout) is flushed with every prompt (shell.c:422) but stderr is not.
>
Stderr is suppose to be unbuffered so that flushing is not required. Or is
that different for windows?
> In some situations this leads to no error messages being displayed until
> the stderr buffer fills.
>
> This happens when running the official sqlite3 binary as subprocess of
> Emacs under Windows 7. The error messages do not appear in a timely
> fashion. I was unable to trigger the misbehavior in a plain shell so my
> only demo is a bit of Emacs Lisp. When this Elisp code below is run, a
> buffer will pop up that *should* contain the output of .help. Under
> Windows it does not. The same occurs even when it's launched via a shell
> subprocess using "2>&1", so it's not simply an issue with Emacs not
> reading from the subprocess's stderr output fast enough.
>
> (let* ((buffer (generate-new-buffer "sqlite"))
> (proc (start-process "sqlite" buffer "sqlite3" "-interactive")))
> (process-send-string proc ".help\n")
> (pop-to-buffer buffer))
>
> I suspect it has to do with being compiled without readline, which is
> why it behaves better elsewhere. I couldn't figure out how to link with
> libreadline on Windows, though, so I couldn't test this.
>
> With the following change to the amalgamation release I got the behavior
> I was looking for: timely error messages from the SQLite command line
> shell. I understand this is probably not the Right Way to do this, but
> it's just a demonstation of a possible fix.
>
> --- a/shell.c
> +++ b/shell.c
> @@ -418,6 +418,7 @@ static char *one_input_line(FILE *in, char *zPrior,
> int isCont
> zResult = readline(zPrompt);
> if( zResult && *zResult ) add_history(zResult);
> #else
> + fflush(stderr);
> printf("%s", zPrompt);
> fflush(stdout);
> zResult = local_getline(zPrior, stdin);
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>
--
D. Richard Hipp
d...@sqlite.org
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