refs: implement releasing ref storages

Ref storages are typically only initialized once for `the_repository`
and then never released. Until now we got away with that without causing
memory leaks because `the_repository` stays reachable, and because the
ref backend is reachable via `the_repository` its memory basically never
leaks.

This is about to change though because of the upcoming migration logic,
which will create a secondary ref storage. In that case, we will either
have to release the old or new ref storage to avoid leaks.

Implement a new `release` callback and expose it via a new
`ref_storage_release()` function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index c3d5f0a6cd..8624477e19 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -529,6 +529,10 @@ struct ref_store;
 typedef struct ref_store *ref_store_init_fn(struct repository *repo,
 					    const char *gitdir,
 					    unsigned int flags);
+/*
+ * Release all memory and resources associated with the ref store.
+ */
+typedef void ref_store_release_fn(struct ref_store *refs);
 
 typedef int ref_store_create_on_disk_fn(struct ref_store *refs,
 					int flags,
@@ -668,6 +672,7 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 struct ref_storage_be {
 	const char *name;
 	ref_store_init_fn *init;
+	ref_store_release_fn *release;
 	ref_store_create_on_disk_fn *create_on_disk;
 
 	ref_transaction_prepare_fn *transaction_prepare;