make Unix.sleepf available under all OCaml versions

ChangeLog

@@ -3,7 +3,10 @@ Changelog
 
 ## NEXT_RELEASE
 
-... cool features to come.
+- Unix.sleepf is provided across all OCaml versions;
+  previously it was only for OCaml >= 4.03.0
+  #930
+  (Francois Berenger, review by Cedric Cellier)
 
 ## v2.10.0 (minor release)
 

src/batUnix.mliv

@@ -1144,10 +1144,10 @@ val alarm : int -> int
 val sleep : int -> unit
 (** Stop execution for the given number of seconds. *)
 
-##V>=4.3##val sleepf : float -> unit
-##V>=4.3##(** Stop execution for the given number of seconds.  Like [sleep],
-##V>=4.3##    but fractions of seconds are supported.
-##V>=4.3##    @since 2.5.0 and OCaml 4.03 *)
+val sleepf : float -> unit
+(** Stop execution for the given number of seconds.  Like [sleep],
+    but fractions of seconds are supported.
+    @since 2.5.0 *)
 
 val times : unit -> process_times
 (** Return the execution times of the process. *)

src/batUnix.mlv

@@ -30,6 +30,37 @@ include Unix
 ##V<4.2##let send_substring = send
 ##V<4.2##let sendto_substring = sendto
 
+##V<4.3##let sleepf (timeout: float): unit =
+##V<4.3##  let elapsed = ref 0.0 in
+##V<4.3##  while !elapsed < timeout do
+##V<4.3##    let start = gettimeofday () in
+##V<4.3##    begin
+##V<4.3##      try ignore(select [] [] [] (timeout -. !elapsed))
+##V<4.3##      with Unix_error(EINTR, _, _) -> ()
+##V<4.3##    end;
+##V<4.3##    let stop = gettimeofday () in
+##V<4.3##    let dt = stop -. start in
+##V<4.3##    elapsed := !elapsed +. dt
+##V<4.3##  done;
+##V<4.3##  ()
+
+(* chronometer is useful to test sleepf *)
+(*$inject
+let chronometer f =
+  let start = gettimeofday () in
+  let res = f () in
+  let stop = gettimeofday () in
+  let dt = stop -. start in
+  (dt, res) ;;
+*)
+
+(* do not underestimate the imprecission of sleepf
+   and so don't be too harsh when testing it *)
+(*$T sleepf
+let dt, _ = chronometer (fun () -> sleepf 0.002) in \
+0.001 <= dt && dt <= 0.003
+*)
+
 let run_and_read cmd =
   (* This code is before the open of BatInnerIO
      to avoid using batteries' wrapped IOs *)