Merge pull request #55 from jestabro/vyconfd-restart

T7980: add write_internal_atomic to cache config in presence of readers

2 files changed, 27 insertions, 0 deletions

diff --git a/src/internal.ml b/src/internal.ml
index 5ee3926..cd7e968 100644
--- a/src/internal.ml
+++ b/src/internal.ml
@@ -1,3 +1,8 @@
+(*
+ * A functor for 'internal' representation of Config_tree and Reference_tree.
+ * This is useful for avoiding re-parsing *_trees on cache and load.
+ *)
+
 exception Read_error of string
 exception Write_error of string
 
@@ -12,6 +17,7 @@ module type T =
 module type FI = functor (M: T) ->
     sig
         val write_internal : M.t -> string -> unit
+        val write_internal_atomic : M.t -> string -> unit
         val read_internal : string -> M.t
         val replace_internal : string -> string -> unit
     end
@@ -44,6 +50,26 @@ module Make : FI = functor (M: T) -> struct
         let ct = Result.value ct_res ~default:M.default in
         close_in_noerr ic; ct
 
+    let write_internal_atomic x file_name =
+        let file_name_tmp = file_name ^ ".tmp" in
+        let yt = M.to_yojson x in
+        let ys = Yojson.Safe.to_string yt in
+        let fd =
+            try
+                Unix.openfile file_name_tmp [Unix.O_CREAT;Unix.O_WRONLY] 0o664
+            with Unix.Unix_error (e,f,p) ->
+                let out =
+                    Printf.sprintf "%s %s: %s" (Unix.error_message e) f p
+                in raise (Write_error out)
+        in
+        let oc = Unix.out_channel_of_descr fd in
+        let () = Unix.ftruncate fd 0 in
+        let () = Printf.fprintf oc "%s" ys in
+        let () = Unix.fsync fd in
+        let () = Unix.chmod file_name_tmp 0o664 in
+        let () = Unix.rename file_name_tmp file_name in
+        close_out_noerr oc
+
     let replace_internal dst src =
         let tmp = src ^ ".tmp" in
         try
diff --git a/src/internal.mli b/src/internal.mli
index a82232d..4fc9b10 100644
--- a/src/internal.mli
+++ b/src/internal.mli
@@ -12,6 +12,7 @@ module type T =
 module type FI = functor (M : T) ->
     sig
       val write_internal : M.t -> string -> unit
+      val write_internal_atomic : M.t -> string -> unit
       val read_internal : string -> M.t
       val replace_internal : string -> string -> unit
     end