Re: [PATCH] reset cached ident date before creating objects
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Jul 29, 2016, 18:15 UTC
- Message-ID
- <xmqqeg6cnwdw.fsf@gitster.mtv.corp.google.com>
- In-Reply-To
- <20160729180517.GA14953@sigill.intra.peff.net>
Jeff King <peff@peff.net> writes:
> Linus suggested resetting the timestamp after making the commit, to > clear the way for the next commit. But if we reset any cached value > _before_ making the commit, this has a few advantages:
I guess our mails crossed ;-).
Show 5 quoted lines
> It does feel a little backwards to cache by default, and then try to > catch all the places that want to reset. Another way of thinking about > it would be to almost _never_ cache, but let a few callsites like (the > commit object creation) explicitly ask for a stable timestamp between > the author and committer.
... and the reflog?
I would say that the approach taken by this version is perfectly sensible, if we don't look at it as a "cache" and instead look at it as a "snapshot" of the clock for the duration of the operation. "reset" is like "now we are starting another operation, so grab a snapshot please".
The changes to both tagging and committing look sensible. Thanks.
Show 107 quoted lines
> -- >8 --
> Subject: reset cached ident date before creating objects
>
> When we compute the date to put in author/committer lines of
> commits, or tagger lines of tags, we get the current date
> once and then cache it for the rest of the program. This is
> a good thing in some cases, like "git commit", because it
> means we do not racily assign different times to the
> author/committer fields of a single commit object.
>
> But as more programs start to make many commits in a single
> process (e.g., the recently builtin "git am"), it means that
> you'll get long strings of commits with identical committer
> timestamps (whereas before, we invoked "git commit" many
> times and got true timestamps).
>
> This patch addresses it by letting callers reset the cached
> time, which means they'll get a fresh time on their next
> call to git_committer_info() or git_author_info(). We do so
> automatically before filling in the ident fields of commit
> and tag objects. That retains the property that committers
> and authors in a single object will match, but means that
> separate objects we create should always get their own
> fresh timestamps.
>
> There's no automated test, because it would be inherently
> racy (it depends on whether the program takes multiple
> seconds to run). But you can see the effect with something
> like:
>
> # make a fake 100-patch series; use --first-parent
> # so that we pretend merges are just more patches
> top=$(git rev-parse HEAD)
> bottom=$(git rev-list --first-parent -100 HEAD | tail -n 1)
> git log --format=email --reverse --first-parent \
> --binary -m -p $bottom..$top >patch
>
> # now apply it; this presumably takes multiple seconds
> git checkout --detach $bottom
> git am <patch
>
> # now count the number of distinct committer times;
> # prior to this patch, there would only be one, but
> # now we'd typically see several.
> git log --format=%ct $bottom.. | sort -u
>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> builtin/tag.c | 1 +
> cache.h | 1 +
> commit.c | 1 +
> ident.c | 5 +++++
> 4 files changed, 8 insertions(+)
>
> diff --git a/builtin/tag.c b/builtin/tag.c
> index 50e4ae5..3025e7f 100644
> --- a/builtin/tag.c
> +++ b/builtin/tag.c
> @@ -225,6 +225,7 @@ static void create_tag(const unsigned char *object, const char *tag,
> if (type <= OBJ_NONE)
> die(_("bad object type."));
>
> + reset_ident_date();
> header_len = snprintf(header_buf, sizeof(header_buf),
> "object %s\n"
> "type %s\n"
> diff --git a/cache.h b/cache.h
> index b5f76a4..31e65f9 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -1269,6 +1269,7 @@ extern const char *ident_default_email(void);
> extern const char *git_editor(void);
> extern const char *git_pager(int stdout_is_tty);
> extern int git_ident_config(const char *, const char *, void *);
> +extern void reset_ident_date(void);
>
> struct ident_split {
> const char *name_begin;
> diff --git a/commit.c b/commit.c
> index 71a360d..7ddbffe 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -1548,6 +1548,7 @@ int commit_tree_extended(const char *msg, size_t msg_len,
> }
>
> /* Person/date information */
> + reset_ident_date();
> if (!author)
> author = git_author_info(IDENT_STRICT);
> strbuf_addf(&buffer, "author %s\n", author);
> diff --git a/ident.c b/ident.c
> index 139c528..e20a772 100644
> --- a/ident.c
> +++ b/ident.c
> @@ -184,6 +184,11 @@ static const char *ident_default_date(void)
> return git_default_date.buf;
> }
>
> +void reset_ident_date(void)
> +{
> + strbuf_reset(&git_default_date);
> +}
> +
> static int crud(unsigned char c)
> {
> return c <= 32 ||