Add Time.now and Time.sleep_until

Providers now provide `sleep_until`. `sleep` is implemented using that.
This makes things a little more precise.

README.md

@@ -22,6 +22,7 @@ unreleased repository.
 * [Networking](#networking)
 * [Design note: object capabilities](#design-note-object-capabilities)
 * [Filesystem access](#filesystem-access)
+* [Time](#time)
 * [Multicore support](#multicore-support)
 * [Design note: thread-safety](#design-note-thread-safety)
 * [Design note: determinism](#design-note-determinism)
@@ -507,6 +508,24 @@ A program that operates on the current directory will probably want to use `cwd`
 whereas a program that accepts a path from the user will probably want to use `fs`,
 perhaps with `open_dir` to constrain all access to be within that directory.
 
+## Time
+
+The standard environment provides a clock with the usual POSIX time:
+
+```ocaml
+# Eio_main.run @@ fun env ->
+  let clock = Eio.Stdenv.clock env in
+  traceln "The time is now %f" (Eio.Time.now clock);
+  Eio.Time.sleep clock 1.0;
+  traceln "The time is now %f" (Eio.Time.now clock)
+The time is now 1623940778.270336
+The time is now 1623940779.270336
+- : unit = ()
+```
+
+You might like to replace this clock with a mock for tests.
+In fact, this README does just that - see [doc/prelude.ml](doc/prelude.ml) for the fake clock used in the example above!
+
 ## Multicore support
 
 Fibres are scheduled cooperatively within a single domain, but you can also create new domains that run in parallel.

doc/prelude.ml

@@ -3,8 +3,34 @@
 module Eio_main = struct
   open Eio.Std
 
+  let now = ref 1623940778.27033591
+
+  let fake_clock real_clock = object (_ : #Eio.Time.clock)
+    method now = !now
+    method sleep_until ?sw time =
+      (* The fake times are all in the past, so we just ask to wait until the
+         fake time is due and it will happen immediately. If we wait for
+         multiple times, they'll get woken in the right order. At the moment,
+         the scheduler only checks for expired timers when the run-queue is
+         empty, so this is a convenient way to wait for the system to be idle.
+         Will need revising if we make the scheduler fair at some point. *)
+      Eio.Time.sleep_until ?sw real_clock time;
+      now := max !now time
+  end
+
+  (* https://github.com/ocaml/ocaml/issues/10324 *)
+  let dontcrash = Sys.opaque_identity
+
   let run fn =
     Eio_main.run @@ fun env ->
-    try fn env
+    try
+      fn @@ object
+        method net        = dontcrash env#net
+        method stdin      = dontcrash env#stdin
+        method stdout     = dontcrash env#stdout
+        method cwd        = dontcrash env#cwd
+        method domain_mgr = dontcrash env#domain_mgr
+        method clock      = fake_clock env#clock
+      end
     with Failure msg -> traceln "Error: %s" msg
 end

lib_eio/eio.ml

@@ -169,10 +169,15 @@ end
 
 module Time = struct
   class virtual clock = object
-    method virtual sleep : ?sw:Switch.t -> float -> unit
+    method virtual now : float
+    method virtual sleep_until : ?sw:Switch.t -> float -> unit
   end
 
-  let sleep ?sw (t : #clock) d = t#sleep ?sw d
+  let now (t : #clock) = t#now
+
+  let sleep_until ?sw (t : #clock) time = t#sleep_until ?sw time
+
+  let sleep ?sw t d = sleep_until ?sw t (now t +. d)
 end
 
 module Dir = struct

lib_eio/eio.mli

@@ -363,9 +363,17 @@ end
 
 module Time : sig
   class virtual clock : object
-    method virtual sleep : ?sw:Switch.t -> float -> unit
+    method virtual now : float
+    method virtual sleep_until : ?sw:Switch.t -> float -> unit
   end
 
+  val now : #clock -> float
+  (** [now t] is the current time according to [t]. *)
+
+  val sleep_until : ?sw:Switch.t -> #clock -> float -> unit
+  (** [sleep_until t time] waits until the given time is reached.
+      @param sw The sleep is aborted if the switch is turned off. *)
+
   val sleep : ?sw:Switch.t -> #clock -> float -> unit
   (** [sleep t d] waits for [d] seconds.
       @param sw The sleep is aborted if the switch is turned off. *)

lib_eio_linux/eio_linux.ml

@@ -404,9 +404,9 @@ let free_buf st buf =
   | None -> Uring.Region.free buf
   | Some k -> enqueue_thread st k buf
 
-effect Sleep : Switch.t option * float -> unit
+effect Sleep_until : Switch.t option * float -> unit
-let sleep ?sw d =
+let sleep_until ?sw d =
-  perform (Sleep (sw, d))
+  perform (Sleep_until (sw, d))
 
 effect ERead : (Switch.t option * Optint.Int63.t option * FD.t * Uring.Region.chunk * amount) -> int
 
@@ -722,7 +722,8 @@ module Objects = struct
   let clock = object
     inherit Eio.Time.clock
 
-    method sleep ?sw d = sleep ?sw d
+    method now = Unix.gettimeofday ()
+    method sleep_until = sleep_until
   end
 
   class dir fd = object
@@ -856,9 +857,8 @@ let run ?(queue_depth=64) ?(block_size=4096) main =
       let k = { Suspended.k; tid } in
       enqueue_accept ~sw st k fd client_addr;
       schedule st
-    | effect (Sleep (sw, d)) k ->
+    | effect (Sleep_until (sw, time)) k ->
       let k = { Suspended.k; tid } in
-      let time = Unix.gettimeofday () +. d in
       let cancel_hook = ref Switch.null_hook in
       begin match sw with
         | None ->

lib_eio_linux/eio_linux.mli

@@ -44,8 +44,8 @@ end
 
 (** {1 Time functions} *)
 
-val sleep : ?sw:Switch.t -> float -> unit
+val sleep_until : ?sw:Switch.t -> float -> unit
-(** [sleep s] blocks until (at least) [s] seconds have passed.
+(** [sleep_until time] blocks until the current time is [time].
     @param sw Cancel the sleep if [sw] is turned off. *)
 
 (** {1 Memory allocation functions} *)

lib_eio_linux/tests/basic_eio_linux.ml

@@ -24,7 +24,7 @@ let () =
   let buf = alloc () in
   let _ = read_exactly fd buf 5 in
   Logs.debug (fun l -> l "sleeping at %f" (Unix.gettimeofday ()));
-  sleep 1.0;
+  sleep_until (Unix.gettimeofday () +. 1.0);
   print_endline (Uring.Region.to_string ~len:5 buf);
   let _ = read_exactly fd ~file_offset:(Int63.of_int 3) buf 3 in
   print_endline (Uring.Region.to_string ~len:3 buf);