We use a direct write() to output the results of --batch and
--batch-check. This is good for processes feeding the input
and reading the output interactively, but it introduces
measurable overhead if you do not want this feature. For
example, on linux.git:
$ git rev-list --objects --all | cut -d' ' -f1 >objects
$ time git cat-file --batch-check='%(objectsize)' \
<objects >/dev/null
real 0m5.440s
user 0m5.060s
sys 0m0.384s
This patch adds an option to use regular stdio buffering:
$ time git cat-file --batch-check='%(objectsize)' \
--buffer <objects >/dev/null
real 0m4.975s
user 0m4.888s
sys 0m0.092s
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
This selectively uses fwrite or write_or_die, depending on the buffer
setting. Another option would be to just always use fwrite(), and then
selectively fflush(). It feels kind of wasteful in the non-buffered
case, as it's just another layer to write through. OTOH, the cost of
writing a line into the buffer only to flush is probably dwarfed by the
system call of actually flushing.
If we went that direction, we could probably simplify the code a bit
(both getting rid of the batch_write function I call here, and dropping
a bunch of existing fflush() calls, where we must flush any time we use
printf for its formatting capabilities).
I also considered that the "--buffer" case is likely to be the common
one. We cannot flip the default, though, as it would break any existing
callers (who would need to specify "--no-buffer"). We can do the usual
deprecation dance, but I don't know if it is worth it for a plumbing
command like this.
Documentation/git-cat-file.txt | 7 +++++++
builtin/cat-file.c | 26 +++++++++++++++++++-------
2 files changed, 26 insertions(+), 7 deletions(-)
diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt
index 319ab4c..0058bd4 100644
--- a/Documentation/git-cat-file.txt
+++ b/Documentation/git-cat-file.txt
@@ -69,6 +69,13 @@ OPTIONS
not be combined with any other options or arguments. See the
section `BATCH OUTPUT` below for details.
+--buffer::
+ Normally batch output is flushed after each object is output, so
+ that a process can interactively read and write from
+ `cat-file`. With this option, the output uses normal stdio
+ buffering; this is much more efficient when invoking
+ `--batch-check` on a large number of objects.
+
--allow-unknown-type::
Allow -s or -t to query broken/corrupt objects of unknown type.
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index d4101b7..741e100 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -14,6 +14,7 @@ struct batch_options {
int enabled;
int follow_symlinks;
int print_contents;
+ int buffer_output;
const char *format;
};
@@ -211,14 +212,25 @@ static size_t expand_format(struct strbuf *sb, const char *start, void *data)
return end - start + 1;
}
-static void print_object_or_die(int fd, struct expand_data *data)
+static void batch_write(struct batch_options *opt, const void *data, int len)
+{
+ if (opt->buffer_output) {
+ if (fwrite(data, 1, len, stdout) != len)
+ die_errno("unable to write to stdout");
+ } else
+ write_or_die(1, data, len);
+}
+
+static void print_object_or_die(struct batch_options *opt, struct expand_data *data)
{
const unsigned char *sha1 = data->sha1;
assert(data->info.typep);
if (data->type == OBJ_BLOB) {
- if (stream_blob_to_fd(fd, sha1, NULL, 0) < 0)
+ if (opt->buffer_output)
+ fflush(stdout);
+ if (stream_blob_to_fd(1, sha1, NULL, 0) < 0)
die("unable to stream %s to stdout", sha1_to_hex(sha1));
}
else {
@@ -234,12 +246,11 @@ static void print_object_or_die(int fd, struct expand_data *data)
if (data->info.sizep && size != data->size)
die("object %s changed size!?", sha1_to_hex(sha1));
- write_or_die(fd, contents, size);
+ batch_write(opt, contents, size);
free(contents);
}
}
-
static int batch_one_object(const char *obj_name, struct batch_options *opt,
struct expand_data *data)
{
@@ -294,12 +305,12 @@ static int batch_one_object(const char *obj_name, struct batch_options *opt,
strbuf_expand(&buf, opt->format, expand_format, data);
strbuf_addch(&buf, '\n');
- write_or_die(1, buf.buf, buf.len);
+ batch_write(opt, buf.buf, buf.len);
strbuf_release(&buf);
if (opt->print_contents) {
- print_object_or_die(1, data);
- write_or_die(1, "\n", 1);
+ print_object_or_die(opt, data);
+ batch_write(opt, "\n", 1);
}
return 0;
}
@@ -415,6 +426,7 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
N_("for blob objects, run textconv on object's content"), 'c'),
OPT_BOOL(0, "allow-unknown-type", &unknown_type,
N_("allow -s and -t to work with broken/corrupt objects")),
+ OPT_BOOL(0, "buffer", &batch.buffer_output, N_("buffer --batch output")),
{ OPTION_CALLBACK, 0, "batch", &batch, "format",
N_("show info and content of objects fed from the standard input"),
PARSE_OPT_OPTARG, batch_option_callback },
--
2.4.4.719.g3984bc6
--
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