odb/source: make reprepare() function pluggable

Introduce a new callback function in `struct odb_source` to make the
function pluggable.

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

Author: pks-t

odb.c

@@ -1119,11 +1119,8 @@ void odb_reprepare(struct object_database *o)
 	o->loaded_alternates = 0;
 	odb_prepare_alternates(o);
 
-	for (source = o->sources; source; source = source->next) {
-		struct odb_source_files *files = odb_source_files_downcast(source);
-		odb_source_loose_reprepare(source);
-		packfile_store_reprepare(files->packed);
-	}
+	for (source = o->sources; source; source = source->next)
+		odb_source_reprepare(source);
 
 	o->approximate_object_count_valid = 0;
 

odb/source-files.c

@@ -28,6 +28,13 @@ static void odb_source_files_free(struct odb_source *source)
 	free(files);
 }
 
+static void odb_source_files_reprepare(struct odb_source *source)
+{
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	odb_source_loose_reprepare(&files->base);
+	packfile_store_reprepare(files->packed);
+}
+
 struct odb_source_files *odb_source_files_new(struct object_database *odb,
 					      const char *path,
 					      bool local)
@@ -40,6 +47,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->packed = packfile_store_new(&files->base);
 
 	files->base.free = odb_source_files_free;
+	files->base.reprepare = odb_source_files_reprepare;
 
 	/*
 	 * Ideally, we would only ever store absolute paths in the source. This

odb/source.h

@@ -57,6 +57,13 @@ struct odb_source {
 	 * all associated resources. The function will never be called with a NULL pointer.
 	 */
 	void (*free)(struct odb_source *source);
+
+	/*
+	 * This callback is expected to clear underlying caches of the object
+	 * database source. The function is called when the repository has for
+	 * example just been repacked so that new objects will become visible.
+	 */
+	void (*reprepare)(struct odb_source *source);
 };
 
 /*
@@ -96,4 +103,14 @@ void odb_source_free(struct odb_source *source);
  */
 void odb_source_release(struct odb_source *source);
 
+/*
+ * Reprepare the object database source and clear any caches. Depending on the
+ * backend used this may have the effect that concurrently-written objects
+ * become visible.
+ */
+static inline void odb_source_reprepare(struct odb_source *source)
+{
+	source->reprepare(source);
+}
+
 #endif