refs.c: add a new flag for transaction delete for refs we know are packed only

Add a new flag REF_ISPACKONLY that we can use in ref_transaction_delete.
This flag indicates that the ref does not exist as a loose ref andf only as
a packed ref. If this is the case we then change the commit code so that
we skip taking out a lock file and we skip calling delete_ref_loose.
Check for this flag and die(BUG:...) if used with _update or _create.

At the start of the transaction, before we even start locking any refs,
we add all such REF_ISPACKONLY refs to delnames so that we have a list of
all pack only refs that we will be deleting during this transaction.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/refs.c b/refs.c
index 69ad51d62e..f458ff9f9d 100644
--- a/refs.c
+++ b/refs.c
@@ -33,6 +33,10 @@ static inline int bad_ref_char(int ch)
  *  pruned.
  */
 #define REF_ISPRUNING	0x0100
+/** Deletion of a ref that only exists as a packed ref in which case we do not
+ *  need to lock the loose ref during the transaction.
+ */
+#define REF_ISPACKONLY	0x0200
 
 /*
  * Try to read one refname component from the front of refname.  Return
@@ -3346,6 +3350,9 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	if (transaction->status != REF_TRANSACTION_OPEN)
 		die("BUG: update on transaction that is not open");
 
+	if (flags & REF_ISPACKONLY)
+		die("BUG: REF_ISPACKONLY can not be used with updates");
+
 	update = add_update(transaction, refname);
 	hashcpy(update->new_sha1, new_sha1);
 	update->flags = flags;
@@ -3370,6 +3377,9 @@ int ref_transaction_create(struct ref_transaction *transaction,
 	if (transaction->status != REF_TRANSACTION_OPEN)
 		die("BUG: create on transaction that is not open");
 
+	if (flags & REF_ISPACKONLY)
+		die("BUG: REF_ISPACKONLY can not be used with creates");
+
 	update = add_update(transaction, refname);
 
 	hashcpy(update->new_sha1, new_sha1);
@@ -3483,10 +3493,20 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	if (ret)
 		goto cleanup;
 
+	for (i = 0; i < n; i++) {
+		struct ref_update *update = updates[i];
+
+		if (update->flags & REF_ISPACKONLY)
+			delnames[delnum++] = update->refname;
+	}
+
 	/* Acquire all locks while verifying old values */
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
+		if (update->flags & REF_ISPACKONLY)
+			continue;
+
 		update->lock = lock_ref_sha1_basic(update->refname,
 						   (update->have_old ?
 						    update->old_sha1 :
@@ -3524,6 +3544,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
+		if (update->flags & REF_ISPACKONLY)
+			continue;
+
 		if (update->lock) {
 			ret |= delete_ref_loose(update->lock, update->type,
 						err);