CP-307958: Use Atomic.t for DB ref

The double ref is not needed, replace it with an Atomic.t

No functional change.

Signed-off-by: Edwin Török <[email protected]>

Author: edwintorok

ocaml/database/db_backend.ml

@@ -21,11 +21,11 @@ let db_FLUSH_TIMER = 2.0
 
 (* --------------------- Util functions on db datastructures *)
 
-let master_database = ref (Db_cache_types.Database.make Schema.empty)
+let master_database = Atomic.make (Db_cache_types.Database.make Schema.empty)
 
-let __test_set_master_database db = master_database := db
+let __test_set_master_database db = Atomic.set master_database db
 
-let make () = Db_ref.in_memory (ref master_database)
+let make () = Db_ref.in_memory master_database
 
 (* !!! Right now this is called at cache population time. It would probably be preferable to call it on flush time instead, so we
    don't waste writes storing non-persistent field values on disk.. At the moment there's not much to worry about, since there are

ocaml/database/db_ref.ml

@@ -12,22 +12,22 @@
  * GNU Lesser General Public License for more details.
  *)
 
-type t = In_memory of Db_cache_types.Database.t ref ref | Remote
+type t = In_memory of Db_cache_types.Database.t Atomic.t | Remote
 
 exception Database_not_in_memory
 
-let in_memory (rf : Db_cache_types.Database.t ref ref) = In_memory rf
+let in_memory (rf : Db_cache_types.Database.t Atomic.t) = In_memory rf
 
 let get_database = function
   | In_memory x ->
-      !(!x)
+      Atomic.get x
   | Remote ->
       raise Database_not_in_memory
 
 let update_database t f =
   match t with
   | In_memory x ->
       let d : Db_cache_types.Database.t = f (get_database t) in
-      !x := d
+      Atomic.set x d
   | Remote ->
       raise Database_not_in_memory

ocaml/database/db_ref.mli

@@ -12,11 +12,11 @@
  * GNU Lesser General Public License for more details.
  *)
 
-type t = In_memory of Db_cache_types.Database.t ref ref | Remote
+type t = In_memory of Db_cache_types.Database.t Atomic.t | Remote
 
 exception Database_not_in_memory
 
-val in_memory : Db_cache_types.Database.t ref ref -> t
+val in_memory : Db_cache_types.Database.t Atomic.t -> t
 
 val get_database : t -> Db_cache_types.Database.t
 

ocaml/xapi/pool_db_backup.ml

@@ -192,7 +192,7 @@ let restore_from_xml __context dry_run (xml_filename : string) =
       (Db_xml.From.file (Datamodel_schema.of_datamodel ()) xml_filename)
   in
   version_check db ;
-  let db_ref = Db_ref.in_memory (ref (ref db)) in
+  let db_ref = Db_ref.in_memory (Atomic.make db) in
   let new_context = Context.make ~database:db_ref "restore_db" in
   prepare_database_for_restore ~old_context:__context ~new_context ;
   (* write manifest and unmarshalled db directly to db_temporary_restore_path, so its ready for us on restart *)

ocaml/xapi/xapi_session.ml

@@ -1569,5 +1569,5 @@ let create_from_db_file ~__context ~filename =
     Xapi_database.Db_xml.From.file (Datamodel_schema.of_datamodel ()) filename
     |> Xapi_database.Db_upgrade.generic_database_upgrade
   in
-  let db_ref = Some (Xapi_database.Db_ref.in_memory (ref (ref db))) in
+  let db_ref = Some (Xapi_database.Db_ref.in_memory (Atomic.make db)) in
   create_readonly_session ~__context ~uname:"db-from-file" ~db_ref

ocaml/xapi/xapi_vdi_helpers.ml

@@ -184,7 +184,7 @@ let database_ref_of_vdi ~__context ~vdi =
     debug "Enabling redo_log with device reason [%s]" device ;
     Redo_log.enable_block_existing log device ;
     let db = Database.make (Datamodel_schema.of_datamodel ()) in
-    let db_ref = Xapi_database.Db_ref.in_memory (ref (ref db)) in
+    let db_ref = Xapi_database.Db_ref.in_memory (Atomic.make db) in
     Redo_log_usage.read_from_redo_log log Xapi_globs.foreign_metadata_db db_ref ;
     Redo_log.delete log ;
     (* Upgrade database to the local schema. *)