[merge] forked global tenv merge

Summary:
In Buck/Java the global type environments of each buck target captured need to be merged. So do the capture DBs. These two tasks can be done concurrently, as both have a computation and an I/O component, and interleaving them should improve perf.

Indeed, profiling the merge process with `offcputime.py` and `cpudist.py` (BPF tools) showed a significant amount of off-cpu time in tests (>40%) as well as a distribution of timings for off-cpu intervals that agrees with IO on a fast medium (ssd).

This diff forks a process to merge the type environments while doing the DB merge as normal. Initial results show an almost 2x improvement.

Reviewed By: skcho

Differential Revision: D28438808

fbshipit-source-id: 89c96f25b

infer/src/backend/mergeCapture.ml

@@ -12,22 +12,47 @@ module YBU = Yojson.Basic.Util
 
 (** Module to merge the results of capture for different buck targets. *)
 
-let merge_global_tenvs infer_deps_file =
-  let time0 = Mtime_clock.counter () in
-  let global_tenv = Tenv.create () in
-  let merge infer_out_src =
-    let global_tenv_path =
-      ResultsDirEntryName.get_path ~results_dir:infer_out_src JavaGlobalTypeEnvironment
-      |> DB.filename_from_string
+module TenvMerger = struct
+  let merge_global_tenvs infer_deps_file =
+    let time0 = Mtime_clock.counter () in
+    let global_tenv = Tenv.create () in
+    let merge infer_out_src =
+      let global_tenv_path =
+        ResultsDirEntryName.get_path ~results_dir:infer_out_src JavaGlobalTypeEnvironment
+        |> DB.filename_from_string
+      in
+      Tenv.read global_tenv_path
+      |> Option.iter ~f:(fun tenv -> Tenv.merge ~src:tenv ~dst:global_tenv)
     in
-    Tenv.read global_tenv_path |> Option.iter ~f:(fun tenv -> Tenv.merge ~src:tenv ~dst:global_tenv)
-  in
-  Utils.iter_infer_deps ~project_root:Config.project_root ~f:merge infer_deps_file ;
-  let time1 = Mtime_clock.counter () in
-  Tenv.store_global global_tenv ;
-  L.progress "Merging type environments took %a, of which %a were spent storing the global tenv@."
-    Mtime.Span.pp (Mtime_clock.count time0) Mtime.Span.pp (Mtime_clock.count time1)
+    Utils.iter_infer_deps ~project_root:Config.project_root ~f:merge infer_deps_file ;
+    let time1 = Mtime_clock.counter () in
+    Tenv.store_global global_tenv ;
+    L.progress "Merging type environments took %a, of which %a were spent storing the global tenv@."
+      Mtime.Span.pp (Mtime_clock.count time0) Mtime.Span.pp (Mtime_clock.count time1)
+
+
+  let merge_global_tenvs infer_deps_file =
+    ScubaLogging.execute_with_time_logging "merge_captured_tenvs" (fun () ->
+        merge_global_tenvs infer_deps_file )
+
+
+  let start infer_deps_file =
+    match Unix.fork () with
+    | `In_the_child ->
+        ForkUtils.protect ~f:merge_global_tenvs infer_deps_file ;
+        L.exit 0
+    | `In_the_parent child_pid ->
+        child_pid
+
 
+  let wait child_pid =
+    match Unix.waitpid child_pid with
+    | Error _ as err ->
+        L.die InternalError "Worker terminated abnormally: %s.@\n"
+          (Unix.Exit_or_signal.to_string_hum err)
+    | Ok () ->
+        ()
+end
 
 let merge_json_results infer_out_src json_entry =
   let main_changed_fs_file = ResultsDir.get_path json_entry in
@@ -62,9 +87,9 @@ let merge_captured_targets () =
   let time0 = Mtime_clock.counter () in
   L.progress "Merging captured Buck targets...@\n%!" ;
   let infer_deps_file = ResultsDir.get_path CaptureDependencies in
+  let tenv_merger_child = TenvMerger.start infer_deps_file in
   DBWriter.merge ~infer_deps_file ;
-  ScubaLogging.execute_with_time_logging "merge_captured_tenvs" (fun () ->
-      merge_global_tenvs infer_deps_file ) ;
+  TenvMerger.wait tenv_merger_child ;
   let targets_num =
     let counter = ref 0 in
     let incr_counter _line = incr counter in