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

I have moved the patch to add &err to ref_transaction_begin to the
current patch series.

Please see
https://github.com/rsahlberg/git/tree/ref-transactions

On Mon, May 19, 2014 at 10:16 AM, Ronnie Sahlberg [off-list ref] wrote:

On Sat, May 17, 2014 at 6:09 AM, Michael Haggerty [off-list ref] wrote:

quoted

On 05/16/2014 07:37 PM, Ronnie Sahlberg wrote:

quoted

Change tag.c to use ref transactions for all ref updates.

Signed-off-by: Ronnie Sahlberg <redacted>
---
 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.

I add an err argument in the next series. I would prefer we let that
patch remain in the next series to
avoid unbounded growth of the current one.

Ok ?

quoted

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?

I think it is more flexible to allow the caller to manage the lifetime
of the error buffer independently of the transaction.
It would allow a caller to free the transaction early but delay
printing the error message until later.

Or it could be used for a multi transaction caller to use a single err
buffer for all transactions and finally print
all errors in a single error() call at the end.

struct strbuf err = STRBUF_INIT;
... first transaction (... &err)...
... second transaction (... &err)...
... third transaction (... &err)...
error("%s", err.buf);



Similar to how rsync handles errors:
sahlberg@sahlberg1:~$ mkdir foo
sahlberg@sahlberg1:~$ touch foo/foo.1
sahlberg@sahlberg1:~$ touch foo/foo.2
sahlberg@sahlberg1:~$ mkdir bar
sahlberg@sahlberg1:~$ chmod 0500 bar
sahlberg@sahlberg1:~$ rsync -Pav foo/* bar
sending incremental file list
foo.1
           0 100%    0.00kB/s    0:00:00 (xfer#1, to-check=1/2)
foo.2
           0 100%    0.00kB/s    0:00:00 (xfer#2, to-check=0/2)
rsync: mkstemp "/usr/local/google/home/sahlberg/bar/.foo.1.K7dFIP"
failed: Permission denied (13)
rsync: mkstemp "/usr/local/google/home/sahlberg/bar/.foo.2.4WdRsW"
failed: Permission denied (13)

sent 136 bytes  received 50 bytes  372.00 bytes/sec
total size is 0  speedup is 0.00
rsync error: some files/attrs were not transferred (see previous
errors) (code 23) at main.c(1070) [sender=3.0.9]

quoted

quoted

      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/