refs: implement simple transactions for the packed-refs file
Handle simple transactions for the packed-refs file at the
packed_ref_cache level via new functions lock_packed_refs(),
commit_packed_refs(), and rollback_packed_refs().
Only allow the packed ref cache to be modified (via add_packed_ref())
while the packed refs file is locked.
Change clone to add the new references within a transaction.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs.h b/refs.h
index 246bf60..9e5db3a 100644
--- a/refs.h
+++ b/refs.h
@@ -77,12 +77,34 @@
extern void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname);
/*
- * Add a reference to the in-memory packed reference cache. To actually
- * write the reference to the packed-refs file, call pack_refs().
+ * Lock the packed-refs file for writing. Flags is passed to
+ * hold_lock_file_for_update(). Return 0 on success.
+ */
+extern int lock_packed_refs(int flags);
+
+/*
+ * Add a reference to the in-memory packed reference cache. This may
+ * only be called while the packed-refs file is locked (see
+ * lock_packed_refs()). To actually write the packed-refs file, call
+ * commit_packed_refs().
*/
extern void add_packed_ref(const char *refname, const unsigned char *sha1);
/*
+ * Write the current version of the packed refs cache from memory to
+ * disk. The packed-refs file must already be locked for writing (see
+ * lock_packed_refs()). Return zero on success.
+ */
+extern int commit_packed_refs(void);
+
+/*
+ * Rollback the lockfile for the packed-refs file, and discard the
+ * in-memory packed reference cache. (The packed-refs file will be
+ * read anew if it is needed again after this function is called.)
+ */
+extern void rollback_packed_refs(void);
+
+/*
* Flags for controlling behaviour of pack_refs()
* PACK_REFS_PRUNE: Prune loose refs after packing
* PACK_REFS_ALL: Pack _all_ refs, not just tags and already packed refs
