Re: [PATCH v10 13/44] tag.c: use ref transactions when doing updates

[Michael Haggerty <mhagger@alum.mit.edu>]

On 05/16/2014 07:37 PM, Ronnie Sahlberg wrote:
> Change tag.c to use ref transactions for all ref updates.
> 
> Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
> ---
>  builtin/tag.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/builtin/tag.c b/builtin/tag.c
> index c6e8a71..b05f9a5 100644
> --- a/builtin/tag.c
> +++ b/builtin/tag.c
> @@ -548,7 +548,6 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  	struct strbuf ref = STRBUF_INIT;
>  	unsigned char object[20], prev[20];
>  	const char *object_ref, *tag;
> -	struct ref_lock *lock;
>  	struct create_tag_options opt;
>  	char *cleanup_arg = NULL;
>  	int annotate = 0, force = 0, lines = -1;
> @@ -556,6 +555,8 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  	const char *msgfile = NULL, *keyid = NULL;
>  	struct msg_arg msg = { 0, STRBUF_INIT };
>  	struct commit_list *with_commit = NULL;
> +	struct ref_transaction *transaction;
> +	struct strbuf err = STRBUF_INIT;
>  	struct option options[] = {
>  		OPT_CMDMODE('l', "list", &cmdmode, N_("list tag names"), 'l'),
>  		{ OPTION_INTEGER, 'n', NULL, &lines, N_("n"),
> @@ -701,11 +702,12 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
>  	if (annotate)
>  		create_tag(object, tag, &buf, &opt, prev, object);
>  
> -	lock = lock_any_ref_for_update(ref.buf, prev, 0, NULL);
> -	if (!lock)
> -		die(_("%s: cannot lock the ref"), ref.buf);
> -	if (write_ref_sha1(lock, object, NULL) < 0)
> -		die(_("%s: cannot update the ref"), ref.buf);
> +	transaction = ref_transaction_begin();
> +	if (!transaction ||
> +	    ref_transaction_update(transaction, ref.buf, object, prev,
> +				   0, !is_null_sha1(prev), &err) ||
> +	    ref_transaction_commit(transaction, NULL, &err))
> +		die("%s", err.buf);

If ref_transaction_begin() fails, then won't err still be empty?  (I
know it can't happen, and you know it can't happen, but should the
caller have to know that?)  It almost seems like ref_transaction_begin()
should have an err parameter, too.

It's kindof late for this question to pop into my head, but: have you
thought about embedding the err strbuf in the transaction object?  I
admit it would make the problem with ref_transaction_begin() even worse,
but maybe it would be a net win in terms of boilerplate?

>  	if (force && !is_null_sha1(prev) && hashcmp(prev, object))
>  		printf(_("Updated tag '%s' (was %s)\n"), tag, find_unique_abbrev(prev, DEFAULT_ABBREV));
>  
> 


-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/