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[PATCH v4 16/27] branch.c: use ref transaction for all ref updates

From
Ronnie Sahlberg <sahlberg@google.com>
Date
Apr 28, 2014, 22:54 UTC
Message-ID
<1398725682-30782-17-git-send-email-sahlberg@google.com>
In-Reply-To
<1398725682-30782-1-git-send-email-sahlberg@google.com>

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@google.com>
---
 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
Previous: Junio C HamanoNext: Ronnie Sahlberg
Message 25 of 38 in “Use ref transactions for all ref updates”
  1. 00/27 Use ref transactions for all ref updatesRonnie Sahlberg, Apr 28, 2014
  2. 01/27 refs.c: constify the sha arguments for ref_transaction_create|delete|updateRonnie Sahlberg, Apr 28, 2014
  3. 02/27 refs.c: allow passing NULL to ref_transaction_freeRonnie Sahlberg, Apr 28, 2014
  4. 03/27 refs.c: add a strbuf argument to ref_transaction_commit for error loggingRonnie Sahlberg, Apr 28, 2014
  5. 04/27 refs.c: make ref_update_reject_duplicates take a strbuf argument for errorsRonnie Sahlberg, Apr 28, 2014
  6. 05/27 update-ref.c: log transaction error from the update_refRonnie Sahlberg, Apr 28, 2014
  7. 06/27 refs.c: make update_ref_write update a strbuf on failureRonnie Sahlberg, Apr 28, 2014
  8. 07/27 refs.c: remove the onerr argument to ref_transaction_commitRonnie Sahlberg, Apr 28, 2014
  9. 08/27 refs.c: change ref_transaction_update() to do error checking and return statusRonnie Sahlberg, Apr 28, 2014
  10. Eric SunshineApr 29, 2014
  11. Ronnie SahlbergApr 29, 2014
  12. 09/27 refs.c: change ref_transaction_create to do error checking and return statusRonnie Sahlberg, Apr 28, 2014
  13. 10/27 refs.c: ref_transaction_delete to check for error and return statusRonnie Sahlberg, Apr 28, 2014
  14. 11/27 tag.c: use ref transactions when doing updatesRonnie Sahlberg, Apr 28, 2014
  15. 12/27 replace.c: use the ref transaction functions for updatesRonnie Sahlberg, Apr 28, 2014
  16. Eric SunshineApr 29, 2014
  17. Ronnie SahlbergApr 29, 2014
  18. Eric SunshineApr 29, 2014
  19. 13/27 commit.c: use ref transactions for updatesRonnie Sahlberg, Apr 28, 2014
  20. 14/27 sequencer.c: use ref transactions for all ref updatesRonnie Sahlberg, Apr 28, 2014
  21. 15/27 fast-import.c: change update_branch to use ref transactionsRonnie Sahlberg, Apr 28, 2014
  22. Eric SunshineApr 29, 2014
  23. Ronnie SahlbergApr 29, 2014
  24. Junio C HamanoApr 29, 2014
  25. 16/27 branch.c: use ref transaction for all ref updatesRonnie Sahlberg, Apr 28, 2014
  26. 17/27 refs.c: change update_ref to use a transactionRonnie Sahlberg, Apr 28, 2014
  27. 18/27 refs.c: free the transaction before returning when number of updates is 0Ronnie Sahlberg, Apr 28, 2014
  28. 19/27 refs.c: ref_transaction_commit should not free the transactionRonnie Sahlberg, Apr 28, 2014
  29. 20/27 fetch.c: clear errno before calling functions that might set itRonnie Sahlberg, Apr 28, 2014
  30. 21/27 fetch.c: change s_update_ref to use a ref transactionRonnie Sahlberg, Apr 28, 2014
  31. 22/27 fetch.c: use a single ref transaction for all ref updatesRonnie Sahlberg, Apr 28, 2014
  32. 23/27 receive-pack.c: use a reference transaction for updating the refsRonnie Sahlberg, Apr 28, 2014
  33. 24/27 fast-import.c: use a ref transaction when dumping tagsRonnie Sahlberg, Apr 28, 2014
  34. 25/27 walker.c: use ref transaction for ref updatesRonnie Sahlberg, Apr 28, 2014
  35. 26/27 refs.c: make write_ref_sha1 staticRonnie Sahlberg, Apr 28, 2014
  36. 27/27 refs.c: make lock_ref_sha1 staticRonnie Sahlberg, Apr 28, 2014
  37. Junio C HamanoApr 29, 2014
  38. Ronnie SahlbergApr 29, 2014

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