Jeff King <peff@xxxxxxxx> wrote:
> On Mon, Jun 27, 2016 at 05:49:48PM -0400, Jeff King wrote:
>
> > So in general I would say that handing non-blocking descriptors to git
> > is not safe.
Indeed. This also makes me wonder if our output to stdout/stderr
suffer from the same theoretical problems if given non-blocking
outputs; I suspect they do.
>> I think it's possible to loop on getdelim() when we see
>> EAGAIN, but I'm not sure if it's worth it.
> The patch for that is below, for the curious. It works with even this:
>
> {
> for i in H E A D; do
> sleep 1
> printf $i
> done
> printf "\n"
> } | nonblock git cat-file --batch-check
>
> Note that I folded the "did we see EAGAIN" check into my sub-function
> (which is the equivalent of your io_wait). You might want to do that in
> the xread() code path, too, as it makes the resulting code there a very
> nice:
>
> if (errno == EINTR)
> continue;
> if (handle_nonblock(fd, POLLIN))
> continue;
Yes :)
> +int handle_nonblock(FILE *fp, short poll_events)
> +{
> + if (ferror(fp) && (errno == EAGAIN || errno == EWOULDBLOCK)) {
<snip>
> + clearerr(fp);
> + return 1;
> + }
> + return 0;
> +}
> +
> +static int getline_stdio_loop(struct strbuf *sb, FILE *fp, int term)
> +{
> + int ch;
> + do {
> + errno = 0;
> + flockfile(fp);
> + while ((ch = getc_unlocked(fp)) != EOF) {
<snip>
> + }
> + funlockfile(fp);
> + } while (handle_nonblock(fp, POLLIN));
I haven't used stdio in a while and I'm glad :)
Error handling with ferror + clearerr + errno checking is
difficult and error-prone.
Linus said this back in 2006, too:
http://mid.gmane.org/Pine.LNX.4.64.0609141023130.4388@xxxxxxxxxxx
So I wonder if we're better off relying entirely on xread/xwrite
+ strbuf for all our buffering.
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