Use a queue to handle tasks in the RestartScheduler

Summary:
The RestartScheduler now uses it's own of_list function to build a
ProcessPool.TaskGenerator to be able to use a queue as the underlying
data structure.

Reviewed By: ngorogiannis

Differential Revision: D19390055

fbshipit-source-id: d57b493b7

infer/src/backend/RestartScheduler.ml

@@ -6,13 +6,23 @@
  *)
 open! IStd
 
+let of_list (lst : 'a list) : 'a ProcessPool.TaskGenerator.t =
+  let content = Queue.of_list lst in
+  let length = ref (Queue.length content) in
+  let remaining_tasks () = !length in
+  let is_empty () = Queue.is_empty content in
+  let finished _finished_item = decr length in
+  let next () = Queue.dequeue content in
+  {remaining_tasks; is_empty; finished; next}
+
+
 (** This behaves exactly the same as the FileScheduler so far. The goal is that it will use a work
     queue and proc locking to avoid repeating work and hopefully get some in process cache hits. *)
 let make sources =
   let gen =
     List.rev_map sources ~f:(fun sf -> SchedulerTypes.File sf)
     |> List.permute ~random_state:(Random.State.make (Array.create ~len:1 0))
-    |> ProcessPool.TaskGenerator.of_list
+    |> of_list
   in
   let next x =
     let res = gen.next x in