From: Eric Wong <e@80x24.org>
To: Jeff King <peff@peff.net>
Cc: Stefan Beller <sbeller@google.com>,
Junio C Hamano <gitster@pobox.com>,
"git@vger.kernel.org" <git@vger.kernel.org>,
Johannes Sixt <j6t@kdbg.org>
Subject: Re: [PATCH 1/2] xread: retry after poll on EAGAIN/EWOULDBLOCK
Date: Mon, 27 Jun 2016 23:19:49 +0000 [thread overview]
Message-ID: <20160627231949.GA23661@dcvr.yhbt.net> (raw)
In-Reply-To: <20160627222238.GA23645@sigill.intra.peff.net>
Jeff King <peff@peff.net> 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@g5.osdl.org
So I wonder if we're better off relying entirely on xread/xwrite
+ strbuf for all our buffering.
next prev parent reply other threads:[~2016-06-27 23:20 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-26 23:21 [PATCH 0/2] wrapper: xread/xwrite fixes for non-blocking FDs Eric Wong
2016-06-26 23:21 ` [PATCH 1/2] xread: retry after poll on EAGAIN/EWOULDBLOCK Eric Wong
2016-06-26 23:42 ` Jeff King
2016-06-27 13:02 ` Junio C Hamano
2016-06-27 14:36 ` Jeff King
2016-06-27 16:49 ` Stefan Beller
2016-06-27 19:17 ` Jeff King
2016-06-27 19:43 ` Stefan Beller
2016-06-27 19:51 ` Jeff King
2016-06-27 20:13 ` Eric Wong
2016-06-27 21:49 ` Jeff King
2016-06-27 22:22 ` Jeff King
2016-06-27 23:19 ` Eric Wong [this message]
2016-06-26 23:51 ` Jeff King
2016-06-27 3:56 ` [PATCHv2 " Eric Wong
2016-06-26 23:21 ` [PATCH 2/2] xwrite: poll on non-blocking FDs Eric Wong
2016-06-26 23:49 ` Jeff King
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160627231949.GA23661@dcvr.yhbt.net \
--to=e@80x24.org \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=j6t@kdbg.org \
--cc=peff@peff.net \
--cc=sbeller@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).