feature: trace loading/marshalling files

Loading/Marshalling can be slow if the files being loaded are huge. We
record the overhead when --trace-file is enabled.

Signed-off-by: Rudi Grinberg <[email protected]>

<!-- ps-id: 5cb1b063-6dd5-4cd7-a081-1d56fab2b6d7 -->

boot/libs.ml

@@ -25,6 +25,9 @@ let local_libraries =
   ; ("otherlibs/dune-glob/src", Some "Dune_glob", false, None)
   ; ("otherlibs/xdg", Some "Xdg", false, None)
   ; ("otherlibs/dune-rpc/private", Some "Dune_rpc_private", false, None)
+  ; ("otherlibs/chrome-trace/src", Some "Chrome_trace", false, None)
+  ; ("vendor/spawn/src", Some "Spawn", false, None)
+  ; ("src/dune_stats", Some "Dune_stats", false, None)
   ; ("vendor/build_path_prefix_map/src", Some "Build_path_prefix_map", false,
     None)
   ; ("src/dune_config", Some "Dune_config", false, None)
@@ -33,13 +36,10 @@ let local_libraries =
   ; ("otherlibs/dune-private-libs/section", Some "Dune_section", false, None)
   ; ("src/dune_lang", Some "Dune_lang", false, None)
   ; ("vendor/opam-file-format", None, false, None)
-  ; ("otherlibs/chrome-trace/src", Some "Chrome_trace", false, None)
   ; ("src/dune_async_io", Some "Dune_async_io", false, None)
   ; ("src/fiber_util", Some "Fiber_util", false, None)
   ; ("src/dune_cache_storage", Some "Dune_cache_storage", false, None)
   ; ("src/dune_cache", Some "Dune_cache", false, None)
-  ; ("vendor/spawn/src", Some "Spawn", false, None)
-  ; ("src/dune_stats", Some "Dune_stats", false, None)
   ; ("otherlibs/dune-action-plugin/src", Some "Dune_action_plugin", false,
     None)
   ; ("src/csexp_rpc", Some "Csexp_rpc", false, None)

src/dune_util/dune

@@ -5,6 +5,8 @@
   (names dune_flock))
  (libraries
   stdune
+  dune_stats
+  chrome_trace
   xdg
   dyn
   ordering

src/dune_util/persistent.ml

@@ -54,8 +54,8 @@ module Make (D : Desc) = struct
         output_string oc magic;
         Marshal.to_channel oc v [])
 
-  let load file =
-    if Path.exists file then
+  let load =
+    let read_file file =
       Io.with_file_in file ~f:(fun ic ->
           match really_input_string ic (String.length magic) with
           | exception End_of_file -> None
@@ -72,7 +72,36 @@ module Make (D : Desc) = struct
                 None
               | d -> Some d
             else None)
-    else None
+    in
+    let read_file =
+      lazy
+        (match Dune_stats.global () with
+        | None -> read_file
+        | Some stats ->
+          fun file ->
+            let start = Unix.gettimeofday () in
+            let res = Result.try_with (fun () -> read_file file) in
+            let event =
+              let stop = Unix.gettimeofday () in
+              let module Event = Chrome_trace.Event in
+              let module Timestamp = Event.Timestamp in
+              let dur = Timestamp.of_float_seconds (stop -. start) in
+              let common =
+                Event.common_fields ~name:"Loading Persistent State"
+                  ~ts:(Timestamp.of_float_seconds start)
+                  ()
+              in
+              let args =
+                [ ("path", `String (Path.to_string file))
+                ; ("module", `String D.name)
+                ]
+              in
+              Event.complete common ~args ~dur
+            in
+            Dune_stats.emit stats event;
+            Result.ok_exn res)
+    in
+    fun file -> if Path.exists file then (Lazy.force read_file) file else None
 end
 
 type t = T : (module Desc with type t = 'a) * 'a -> t