On Wed, Jun 08, 2016 at 03:19:18PM -0400, Jeff King wrote:
> That made me wonder if we could repeatedly reuse a buffer attached to
> the file descriptor. And indeed, isn't that what stdio is? The whole
> reason this buffer exists is because we are using a direct descriptor
> write. If we switched this function to use fprintf(), we'd avoid the
> whole buffer question, have a fixed cap on our memory use (since we just
> flush anytime the buffer is full) _and_ we'd reduce the number of
> write syscalls we're making by almost a factor of 100.
So all of this strbuf discussion aside, I think it is worth doing
something like this for this particular case.
-- >8 --
Subject: send-pack: use buffered I/O to talk to pack-objects
We start a pack-objects process and then write all of the
positive and negative sha1s to it over a pipe. We do so by
formatting each item into a fixed-size buffer and then
writing each individually. This has two drawbacks:
1. There's some manual computation of the buffer size,
which is not immediately obvious is correct (though it
is).
2. We write() once per sha1, which means a lot more system
calls than are necessary.
We can solve both by wrapping the pipe descriptor in a stdio
handle; this is the same technique used by upload-pack when
serving fetches.
Note that we can also simplify and improve the error
handling here. The original detected a single write error
and broke out of the loop (presumably to avoid writing the
error message over and over), but never actually acted on
seeing an error; we just fed truncated input and took
whatever pack-objects returned.
In practice, this probably didn't matter, as the likely
errors would be caused by pack-objects dying (and we'd
probably just die with SIGPIPE anyway). But we can easily
make this simpler and more robust; the stdio handle keeps an
error flag, which we can check at the end.
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
send-pack.c | 33 ++++++++++++++++-----------------
1 file changed, 16 insertions(+), 17 deletions(-)
diff --git a/send-pack.c b/send-pack.c
index 37ee04e..299d303 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -36,18 +36,15 @@ int option_parse_push_signed(const struct option *opt,
die("bad %s argument: %s", opt->long_name, arg);
}
-static int feed_object(const unsigned char *sha1, int fd, int negative)
+static void feed_object(const unsigned char *sha1, FILE *fh, int negative)
{
- char buf[42];
-
if (negative && !has_sha1_file(sha1))
- return 1;
+ return;
- memcpy(buf + negative, sha1_to_hex(sha1), 40);
if (negative)
- buf[0] = '^';
- buf[40 + negative] = '\n';
- return write_or_whine(fd, buf, 41 + negative, "send-pack: send refs");
+ putc('^', fh);
+ fputs(sha1_to_hex(sha1), fh);
+ putc('\n', fh);
}
/*
@@ -73,6 +70,7 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
NULL,
};
struct child_process po = CHILD_PROCESS_INIT;
+ FILE *po_in;
int i;
i = 4;
@@ -97,21 +95,22 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
* We feed the pack-objects we just spawned with revision
* parameters by writing to the pipe.
*/
+ po_in = xfdopen(po.in, "w");
for (i = 0; i < extra->nr; i++)
- if (!feed_object(extra->sha1[i], po.in, 1))
- break;
+ feed_object(extra->sha1[i], po_in, 1);
while (refs) {
- if (!is_null_oid(&refs->old_oid) &&
- !feed_object(refs->old_oid.hash, po.in, 1))
- break;
- if (!is_null_oid(&refs->new_oid) &&
- !feed_object(refs->new_oid.hash, po.in, 0))
- break;
+ if (!is_null_oid(&refs->old_oid))
+ feed_object(refs->old_oid.hash, po_in, 1);
+ if (!is_null_oid(&refs->new_oid))
+ feed_object(refs->new_oid.hash, po_in, 0);
refs = refs->next;
}
- close(po.in);
+ fflush(po_in);
+ if (ferror(po_in))
+ die_errno("error writing to pack-objects");
+ fclose(po_in);
if (args->stateless_rpc) {
char *buf = xmalloc(LARGE_PACKET_MAX);
--
2.9.0.rc2.138.geb72a36
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