Change create_branch to use a ref transaction when creating the new branch.
ref_transaction_create will check that the ref does not already exist and fail
otherwise meaning that we no longer need to keep a lock on the ref during the
setup_tracking. This simplifies the code since we can now do the transaction
in one single step.
If the forcing flag is false then use ref_transaction_create since this will
fail if the ref already exist. Otherwise use ref_transaction_update.
This also fixes a race condition in the old code where two concurrent
create_branch could race since the lock_any_ref_for_update/write_ref_sha1
did not protect against the ref already existsing. I.e. one thread could end up
overwriting a branch even if the forcing flag is false.
Signed-off-by: Ronnie Sahlberg <sahlberg@xxxxxxxxxx>
---
branch.c | 30 ++++++++++++++++--------------
1 file changed, 16 insertions(+), 14 deletions(-)
diff --git a/branch.c b/branch.c
index 660097b..2aa5c82 100644
--- a/branch.c
+++ b/branch.c
@@ -226,7 +226,6 @@ void create_branch(const char *head,
int force, int reflog, int clobber_head,
int quiet, enum branch_track track)
{
- struct ref_lock *lock = NULL;
struct commit *commit;
unsigned char sha1[20];
char *real_ref, msg[PATH_MAX + 20];
@@ -285,15 +284,6 @@ void create_branch(const char *head,
die(_("Not a valid branch point: '%s'."), start_name);
hashcpy(sha1, commit->object.sha1);
- if (!dont_change_ref) {
- lock = lock_any_ref_for_update(ref.buf, NULL, 0, NULL);
- if (!lock)
- die_errno(_("Failed to lock ref for update"));
- }
-
- if (reflog)
- log_all_ref_updates = 1;
-
if (forcing)
snprintf(msg, sizeof msg, "branch: Reset to %s",
start_name);
@@ -301,13 +291,25 @@ void create_branch(const char *head,
snprintf(msg, sizeof msg, "branch: Created from %s",
start_name);
+ if (reflog)
+ log_all_ref_updates = 1;
+
+ if (!dont_change_ref) {
+ struct ref_transaction *transaction;
+ struct strbuf err = STRBUF_INIT;
+
+ transaction = ref_transaction_begin();
+ if (!transaction ||
+ ref_transaction_update(transaction, ref.buf, sha1,
+ null_sha1, 0, !forcing) ||
+ ref_transaction_commit(transaction, msg, &err))
+ die_errno(_("%s: failed to write ref: %s"),
+ ref.buf, err.buf);
+ }
+
if (real_ref && track)
setup_tracking(ref.buf + 11, real_ref, track, quiet);
- if (!dont_change_ref)
- if (write_ref_sha1(lock, sha1, msg) < 0)
- die_errno(_("Failed to write ref"));
-
strbuf_release(&ref);
free(real_ref);
}
--
1.9.1.528.g98b8868.dirty
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