move Time into a proper module in the core, depopt on mtime

src/core/dune

@@ -4,6 +4,9 @@
   (public_name tiny_httpd.core)
   (private_modules parse_ common_)
   (libraries threads seq hmap iostream
+             (select time.ml from
+              (mtime mtime.clock.os -> time.mtime.ml)
+              (unix -> time.default.ml))
              (select log.ml from
               (logs -> log.logs.ml)
               (-> log.default.ml))))

src/core/time.default.ml

@@ -1,3 +1,5 @@
+let now_s = Unix.gettimeofday
+
 let[@inline] now_us () =
   let t = Unix.gettimeofday () in
   t *. 1e6 |> ceil

src/core/time.mli

@@ -0,0 +1,10 @@
+(** Basic time measurement.
+
+    This provides a basic clock, monotonic if [mtime] is installed,
+    or based on [Unix.gettimeofday] otherwise *)
+
+val now_us : unit -> float
+(** Current time in microseconds. The precision should be at least below the millisecond. *)
+
+val now_s : unit -> float
+(** Current time in seconds. The precision should be at least below the millisecond. *)

src/core/time.mtime.ml

@@ -0,0 +1,7 @@
+let[@inline] now_s () =
+  let t = Mtime_clock.now_ns () in
+  Int64.(div t 1_000_000_000L |> to_float)
+
+let[@inline] now_us () =
+  let t = Mtime_clock.now_ns () in
+  Int64.(div t 1000L |> to_float)

src/prometheus/common_p_.ml

@@ -1,3 +1,4 @@
 module A = Tiny_httpd_core.Atomic_
+module Time = Tiny_httpd_core.Time
 
 let spf = Printf.sprintf

src/prometheus/dune

@@ -4,10 +4,7 @@
  (name tiny_httpd_prometheus)
  (public_name tiny_httpd.prometheus)
  (synopsis "Metrics using prometheus")
- (private_modules common_p_ time_)
+ (private_modules common_p_)
  (flags :standard -open Tiny_httpd_core)
  (libraries
-  tiny_httpd.core unix
-  (select time_.ml from
-   (mtime mtime.clock.os -> time_.mtime.ml)
-   (-> time_.default.ml))))
+  tiny_httpd.core unix))

src/prometheus/time_.mli

@@ -1 +0,0 @@
-val now_us : unit -> float

src/prometheus/time_.mtime.ml

@@ -1,3 +0,0 @@
-let[@inline] now_us () =
-  let t = Mtime_clock.now_ns () in
-  Int64.(div t 1000L |> to_float)

src/prometheus/tiny_httpd_prometheus.ml

@@ -189,12 +189,12 @@ let http_middleware (reg : Registry.t) : Server.Middleware.t =
 
   fun h : Server.Middleware.handler ->
     fun req ~resp : unit ->
-     let start = Time_.now_us () in
+     let start = Time.now_us () in
      Counter.incr c_req;
      h req ~resp:(fun (response : Response.t) ->
          let code = response.code in
 
-         let elapsed_us = Time_.now_us () -. start in
+         let elapsed_us = Time.now_us () -. start in
          let elapsed_s = elapsed_us /. 1e6 in
          Histogram.add h_latency elapsed_s;