Merge pull request #308 from samoht/fsync

use fsync to flush metadata when reoperning a file with new headers

CHANGES.md

@@ -9,6 +9,9 @@
   progress: the `log_async` file was not cached properly and fully reloaded
   from disk every time. (#310)
 
+- Added fsync after `Index.clear` to signal more quickly to read-only instances
+  than something has changed in the file (#308)
+
 ## Changed
 
 - Specialise `IO.v` to create read-only or read-write instances. (#291)

src/unix/index_unix.ml

@@ -152,6 +152,7 @@ module IO : Index.IO = struct
         m "[%s] raw set_header %a" file Header.pp { offset; generation });
     Raw.Header.set raw header;
     Raw.Fan.set raw "";
+    Raw.fsync raw;
     raw
 
   let clear ~generation ?(hook = fun () -> ()) ~reopen t =
@@ -202,23 +203,23 @@ module IO : Index.IO = struct
   let v ?flush_callback ~fresh ~generation ~fan_size file =
     let v = v_instance ?flush_callback ~readonly:false file in
     mkdir (Filename.dirname file);
+    let header =
+      { Raw.Header.offset = Int63.zero; version = current_version; generation }
+    in
     match Sys.file_exists file with
     | false ->
         let x = Unix.openfile file Unix.[ O_CREAT; O_CLOEXEC; O_RDWR ] 0o644 in
         let raw = Raw.v x in
-        Raw.Offset.set raw Int63.zero;
+        Raw.Header.set raw header;
         Raw.Fan.set_size raw fan_size;
-        Raw.Version.set raw current_version;
-        Raw.Generation.set raw generation;
         v ~fan_size ~offset:Int63.zero raw
     | true ->
         let x = Unix.openfile file Unix.[ O_EXCL; O_CLOEXEC; O_RDWR ] 0o644 in
         let raw = Raw.v x in
         if fresh then (
-          Raw.Offset.set raw Int63.zero;
+          Raw.Header.set raw header;
           Raw.Fan.set_size raw fan_size;
-          Raw.Version.set raw current_version;
-          Raw.Generation.set raw generation;
+          Raw.fsync raw;
           v ~fan_size ~offset:Int63.zero raw)
         else
           let version = Raw.Version.get raw in