diff --git a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/dune b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/dune
index 663c24437c7..cdaf50ee02f 100644
--- a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/dune
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/dune
@@ -1,16 +1,24 @@
 (library
   (public_name xapi-stdext-threads)
   (name  xapi_stdext_threads)
-  (modules :standard \ threadext_test)
+  (modules :standard \ ipq scheduler threadext_test ipq_test)
   (libraries
     threads.posix
     unix
     xapi-stdext-unix
     xapi-stdext-pervasives)
 )
-(test
-  (name threadext_test)
+
+(library
+  (public_name xapi-stdext-threads.scheduler)
+  (name xapi_stdext_threads_scheduler)
+  (modules ipq scheduler)
+  (libraries mtime mtime.clock threads.posix unix xapi-log xapi-stdext-threads)
+)
+
+(tests
+  (names threadext_test ipq_test)
   (package xapi-stdext-threads)
-  (modules threadext_test)
-  (libraries xapi_stdext_threads alcotest mtime.clock.os mtime fmt threads.posix)
+  (modules threadext_test ipq_test)
+  (libraries xapi_stdext_threads alcotest mtime.clock.os mtime fmt threads.posix xapi_stdext_threads_scheduler)
 )
diff --git a/ocaml/xapi/ipq.ml b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.ml
similarity index 73%
rename from ocaml/xapi/ipq.ml
rename to ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.ml
index ba56825ebe0..4cf29ed3d9b 100644
--- a/ocaml/xapi/ipq.ml
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.ml
@@ -15,15 +15,16 @@
 
 type 'a event = {ev: 'a; time: Mtime.t}
 
-type 'a t = {mutable size: int; mutable data: 'a event array}
+type 'a t = {default: 'a event; mutable size: int; mutable data: 'a event array}
 
 exception EmptyHeap
 
-let create n =
+let create n default =
   if n <= 0 then
     invalid_arg "create"
   else
-    {size= -n; data= [||]}
+    let default = {ev= default; time= Mtime_clock.now ()} in
+    {default; size= 0; data= Array.make n default}
 
 let is_empty h = h.size <= 0
 
@@ -32,16 +33,11 @@ let resize h =
   assert (n > 0) ;
   let n' = 2 * n in
   let d = h.data in
-  let d' = Array.make n' d.(0) in
+  let d' = Array.make n' h.default in
   Array.blit d 0 d' 0 n ;
   h.data <- d'
 
 let add h x =
-  (* first addition: we allocate the array *)
-  if h.size < 0 then (
-    h.data <- Array.make (-h.size) x ;
-    h.size <- 0
-  ) ;
   let n = h.size in
   (* resizing if needed *)
   if n = Array.length h.data then resize h ;
@@ -64,10 +60,21 @@ let maximum h =
 
 let remove h s =
   if h.size <= 0 then raise EmptyHeap ;
+  if s < 0 || s >= h.size then
+    invalid_arg (Printf.sprintf "%s: index %d out of bounds" __FUNCTION__ s) ;
   let n = h.size - 1 in
-  h.size <- n ;
   let d = h.data in
   let x = d.(n) in
+  d.(n) <- h.default ;
+  (* moving [x] up in the heap *)
+  let rec moveup i =
+    let fi = (i - 1) / 2 in
+    if i > 0 && Mtime.is_later d.(fi).time ~than:x.time then (
+      d.(i) <- d.(fi) ;
+      moveup fi
+    ) else
+      d.(i) <- x
+  in
   (* moving [x] down in the heap *)
   let rec movedown i =
     let j = (2 * i) + 1 in
@@ -84,7 +91,13 @@ let remove h s =
     else
       d.(i) <- x
   in
-  movedown s
+  if s = n then
+    ()
+  else if Mtime.is_later d.(s).time ~than:x.time then
+    moveup s
+  else
+    movedown s ;
+  h.size <- n
 
 let find h ev =
   let rec iter n =
@@ -112,32 +125,24 @@ let pop_maximum h =
   let m = maximum h in
   remove h 0 ; m
 
+let check h =
+  let d = h.data in
+  for i = 1 to h.size - 1 do
+    let fi = (i - 1) / 2 in
+    let ordered = Mtime.is_later d.(i).time ~than:d.(fi).time in
+    assert ordered
+  done
+
 let iter f h =
   let d = h.data in
   for i = 0 to h.size - 1 do
     f d.(i)
   done
 
+(*
 let fold f h x0 =
   let n = h.size in
   let d = h.data in
   let rec foldrec x i = if i >= n then x else foldrec (f d.(i) x) (succ i) in
   foldrec x0 0
-
-(*
-let _ =
-  let test : int t = create 100 in
-  for i=0 to 99 do
-    let e = {time=Random.float 10.0; ev=i} in
-    add test e
-  done;
-  for i=0 to 49 do
-    let xx=find test i in
-    remove test xx
-  done;
-(*  remove test xx;*)
-  for i=0 to 49 do
-    let e=pop_maximum test in
-    Printf.printf "time: %f, site: %d\n" e.time e.ev
-  done
 *)
diff --git a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.mli b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.mli
new file mode 100644
index 00000000000..b7c4974e642
--- /dev/null
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.mli
@@ -0,0 +1,58 @@
+(*
+ * Copyright (C) 2024 Cloud Software Group
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+type 'a event = {ev: 'a; time: Mtime.t}
+
+type 'a t
+
+exception EmptyHeap
+
+val create : int -> 'a -> 'a t
+(** [create n default] creates an empty Imperative priority queue.
+   The queue initially is initialized to store [n] elements.
+   The queue will expand beyond [n] automatically if needed.
+   [default] value will the used to fill unused data. *)
+
+val is_empty : 'a t -> bool
+(** Check if the queue is empty *)
+
+val add : 'a t -> 'a event -> unit
+(** Add an event to the queue *)
+
+val remove : 'a t -> int -> unit
+(** Remove an event from the queue passing the index.
+   @raise EmptyHeap if the queue is empty.
+   @raise Invalid_argument if the index is invalid. *)
+
+val find_p : 'a t -> ('a -> bool) -> int
+(** Find the index of an event which matches a given condition
+   or -1 if not found *)
+
+val find : 'a t -> 'a -> int
+(** Find the index of an event which matches a given event
+   or -1 if not found *)
+
+val maximum : 'a t -> 'a event
+(** Return a copy of the event with the next time.
+   @raise EmptyHeap if the queue is empty. *)
+
+val pop_maximum : 'a t -> 'a event
+(** Return and remove the event with the next time.
+   @raise EmptyHeap if the queue is empty. *)
+
+val iter : ('a event -> unit) -> 'a t -> unit
+(** Iterate given function on the list of events in the queue *)
+
+val check : 'a t -> unit
+(** Check internal queue state, used for debugging *)
diff --git a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.ml b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.ml
new file mode 100644
index 00000000000..e8e64093e16
--- /dev/null
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.ml
@@ -0,0 +1,143 @@
+(*
+ * Copyright (C) 2024 Cloud Software Group
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+module Ipq = Xapi_stdext_threads_scheduler.Ipq
+
+(* test we get "out of bound" exception calling Ipq.remove *)
+let test_out_of_index () =
+  let q = Ipq.create 10 0 in
+  Ipq.add q {Ipq.ev= 123; Ipq.time= Mtime_clock.now ()} ;
+  let is_oob = function
+    | Invalid_argument s when String.ends_with ~suffix:"  out of bounds" s ->
+        true
+    | _ ->
+        false
+  in
+  let oob_check n =
+    (Alcotest.match_raises "out of bound" is_oob @@ fun () -> Ipq.remove q n) ;
+    Alcotest.(check bool) "same value" false (Ipq.is_empty q)
+  in
+  oob_check 10 ;
+  oob_check (-1) ;
+  oob_check 9 ;
+  oob_check 1 ;
+  (* this should succeed *)
+  Ipq.remove q 0
+
+(* check queue does not retain some data after being removed *)
+let test_leak () =
+  let default () = () in
+  let q = Ipq.create 10 default in
+  let array = Array.make 1024 'x' in
+  let use_array () = array.(0) <- 'a' in
+  let allocated = Atomic.make true in
+  Gc.finalise (fun _ -> Atomic.set allocated false) array ;
+  Ipq.add q {Ipq.ev= use_array; Ipq.time= Mtime_clock.now ()} ;
+  Ipq.remove q 0 ;
+  Gc.full_major () ;
+  Gc.full_major () ;
+  Alcotest.(check bool) "allocated" false (Atomic.get allocated) ;
+  Ipq.add q {Ipq.ev= default; Ipq.time= Mtime_clock.now ()}
+
+(* test Ipq.is_empty call *)
+let test_empty () =
+  let q = Ipq.create 10 0 in
+  Alcotest.(check bool) "same value" true (Ipq.is_empty q) ;
+  Ipq.add q {Ipq.ev= 123; Ipq.time= Mtime_clock.now ()} ;
+  Alcotest.(check bool) "same value" false (Ipq.is_empty q) ;
+  Ipq.remove q 0 ;
+  Alcotest.(check bool) "same value" true (Ipq.is_empty q)
+
+module Int64Set = Set.Make (Int64)
+
+let check = Ipq.check
+
+(* get size of the queue *)
+let size queue =
+  let l = ref 0 in
+  Ipq.iter (fun _ -> l := !l + 1) queue ;
+  !l
+
+(* get a set of times from the queue *)
+let set queue =
+  let s = ref Int64Set.empty in
+  Ipq.iter
+    (fun d ->
+      let t = d.time in
+      let t = Mtime.to_uint64_ns t in
+      s := Int64Set.add t !s
+    )
+    queue ;
+  !s
+
+let test_old () =
+  let test : int Ipq.t = Ipq.create 100 0 in
+  let s = ref Int64Set.empty in
+  let add i =
+    let ti = Random.int64 1000000L in
+    let t = Mtime.of_uint64_ns ti in
+    let e = {Ipq.time= t; Ipq.ev= i} in
+    Ipq.add test e ;
+    s := Int64Set.add ti !s
+  in
+  for i = 0 to 49 do
+    add i
+  done ;
+  let first_half = set test in
+  for i = 50 to 99 do
+    add i
+  done ;
+  check test ;
+  (* we should have all elements *)
+  Alcotest.(check int) "100 elements" 100 (size test) ;
+
+  let all = set test in
+  Alcotest.(check int) "same list" 0 (Int64Set.compare !s all) ;
+
+  (* remove half of the elements *)
+  for i = 0 to 49 do
+    let xx = Ipq.find test i in
+    Printf.printf "Removing element %d position %d\n%!" i xx ;
+    Ipq.remove test xx ;
+    check test
+  done ;
+  Alcotest.(check int) "50 elements" 50 (size test) ;
+
+  (* make sure we have the right elements in the list *)
+  let s = set test in
+  let second_half = Int64Set.diff all first_half in
+  Alcotest.(check int) "same list" 0 (Int64Set.compare s second_half) ;
+
+  (* remove test *)
+  let prev = ref 0L in
+  for _ = 0 to 49 do
+    let e = Ipq.pop_maximum test in
+    let t = Mtime.to_uint64_ns e.time in
+    Alcotest.(check bool)
+      (Printf.sprintf "%Ld bigger than %Ld" t !prev)
+      true (t >= !prev) ;
+    Printf.printf "time: %Ld, site: %d\n" t e.ev ;
+    prev := t ;
+    check test
+  done
+
+let tests =
+  [
+    ("test_out_of_index", `Quick, test_out_of_index)
+  ; ("test_leak", `Quick, test_leak)
+  ; ("test_empty", `Quick, test_empty)
+  ; ("test_old", `Quick, test_old)
+  ]
+
+let () = Alcotest.run "Ipq" [("generic", tests)]
diff --git a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.mli b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.mli
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/ocaml/xapi/xapi_periodic_scheduler.ml b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
similarity index 82%
rename from ocaml/xapi/xapi_periodic_scheduler.ml
rename to ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
index 1edcb938857..3e8543ec04d 100644
--- a/ocaml/xapi/xapi_periodic_scheduler.ml
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
@@ -12,7 +12,7 @@
  * GNU Lesser General Public License for more details.
  *)
 
-module D = Debug.Make (struct let name = "backgroundscheduler" end)
+module D = Debug.Make (struct let name = __MODULE__ end)
 
 open D
 module Delay = Xapi_stdext_threads.Threadext.Delay
@@ -25,21 +25,27 @@ type t = {func: unit -> unit; ty: func_ty; name: string}
 
 let delay = Delay.make ()
 
-let (queue : t Ipq.t) = Ipq.create 50
+let queue_default = {func= (fun () -> ()); ty= OneShot; name= ""}
+
+let (queue : t Ipq.t) = Ipq.create 50 queue_default
 
 let lock = Mutex.create ()
 
 module Clock = struct
-  (** time span of s seconds *)
   let span s = Mtime.Span.of_uint64_ns (Int64.of_float (s *. 1e9))
 
+  let span_to_s span =
+    Mtime.Span.to_uint64_ns span |> Int64.to_float |> fun ns -> ns /. 1e9
+
   let add_span clock secs =
+    (* return mix or max available value if the add overflows *)
     match Mtime.add_span clock (span secs) with
     | Some t ->
         t
+    | None when secs > 0. ->
+        Mtime.max_stamp
     | None ->
-        raise
-          Api_errors.(Server_error (internal_error, ["clock overflow"; __LOC__]))
+        Mtime.min_stamp
 end
 
 let add_to_queue ?(signal = true) name ty start newfunc =
@@ -59,7 +65,7 @@ let remove_from_queue name =
     Ipq.remove queue index
 
 let loop () =
-  debug "Periodic scheduler started" ;
+  debug "%s started" __MODULE__ ;
   try
     while true do
       let empty = with_lock lock (fun () -> Ipq.is_empty queue) in
@@ -82,8 +88,8 @@ let loop () =
         ) else (* Sleep until next event. *)
           let sleep =
             Mtime.(span next.Ipq.time now)
-            |> Mtime.Span.add (Clock.span 0.001)
-            |> Scheduler.span_to_s
+            |> Mtime.Span.(add ms)
+            |> Clock.span_to_s
           in
           try ignore (Delay.wait delay sleep)
           with e ->
@@ -102,5 +108,5 @@ let loop () =
     done
   with _ ->
     error
-      "Periodic scheduler died! Xapi will no longer function well and should \
-       be restarted."
+      "Scheduler thread died! This daemon will no longer function well and \
+       should be restarted."
diff --git a/ocaml/xapi/xapi_periodic_scheduler.mli b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.mli
similarity index 100%
rename from ocaml/xapi/xapi_periodic_scheduler.mli
rename to ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.mli
diff --git a/ocaml/tests/common/dune b/ocaml/tests/common/dune
index c578f5f9785..29acca3d2cb 100644
--- a/ocaml/tests/common/dune
+++ b/ocaml/tests/common/dune
@@ -26,6 +26,7 @@
     xapi-test-utils
     xapi-types
     xapi-stdext-date
+    xapi-stdext-threads.scheduler
     xapi-stdext-unix
   )
 )
diff --git a/ocaml/tests/common/test_event_common.ml b/ocaml/tests/common/test_event_common.ml
index 149a27d5ea8..9d37c038ab4 100644
--- a/ocaml/tests/common/test_event_common.ml
+++ b/ocaml/tests/common/test_event_common.ml
@@ -2,16 +2,16 @@ let ps_start = ref false
 
 let scheduler_mutex = Mutex.create ()
 
+module Scheduler = Xapi_stdext_threads_scheduler.Scheduler
+
 let start_periodic_scheduler () =
   Mutex.lock scheduler_mutex ;
   if !ps_start then
     ()
   else (
-    Xapi_periodic_scheduler.add_to_queue "dummy"
-      (Xapi_periodic_scheduler.Periodic 60.0) 0.0 (fun () -> ()
-    ) ;
+    Scheduler.add_to_queue "dummy" (Scheduler.Periodic 60.0) 0.0 (fun () -> ()) ;
     Xapi_event.register_hooks () ;
-    ignore (Thread.create Xapi_periodic_scheduler.loop ()) ;
+    ignore (Thread.create Scheduler.loop ()) ;
     ps_start := true
   ) ;
   Mutex.unlock scheduler_mutex
diff --git a/ocaml/xapi/dune b/ocaml/xapi/dune
index 5602e62d152..d2e2fb17de8 100644
--- a/ocaml/xapi/dune
+++ b/ocaml/xapi/dune
@@ -196,6 +196,7 @@
     xapi-stdext-pervasives
     xapi-stdext-std
     xapi-stdext-threads
+    xapi-stdext-threads.scheduler
     xapi-stdext-unix
     xapi-stdext-zerocheck
     xapi-tracing
@@ -256,6 +257,7 @@
     xapi-stdext-pervasives
     xapi-stdext-std
     xapi-stdext-threads
+    xapi-stdext-threads.scheduler
     xapi-stdext-unix
     xapi-types
     xapi_aux
diff --git a/ocaml/xapi/extauth_plugin_ADwinbind.ml b/ocaml/xapi/extauth_plugin_ADwinbind.ml
index fc0aa01ad0b..6f51eea9cc5 100644
--- a/ocaml/xapi/extauth_plugin_ADwinbind.ml
+++ b/ocaml/xapi/extauth_plugin_ADwinbind.ml
@@ -22,6 +22,7 @@ end)
 open D
 open Xapi_stdext_std.Xstringext
 open Auth_signature
+module Scheduler = Xapi_stdext_threads_scheduler.Scheduler
 
 let finally = Xapi_stdext_pervasives.Pervasiveext.finally
 
@@ -1172,16 +1173,14 @@ module ClosestKdc = struct
   let trigger_update ~start =
     if Pool_role.is_master () then (
       debug "Trigger task: %s" periodic_update_task_name ;
-      Xapi_periodic_scheduler.add_to_queue periodic_update_task_name
-        (Xapi_periodic_scheduler.Periodic
-           !Xapi_globs.winbind_update_closest_kdc_interval
-        )
+      Scheduler.add_to_queue periodic_update_task_name
+        (Scheduler.Periodic !Xapi_globs.winbind_update_closest_kdc_interval)
         start update
     )
 
   let stop_update () =
     if Pool_role.is_master () then
-      Xapi_periodic_scheduler.remove_from_queue periodic_update_task_name
+      Scheduler.remove_from_queue periodic_update_task_name
 end
 
 module RotateMachinePassword = struct
@@ -1302,11 +1301,10 @@ module RotateMachinePassword = struct
 
   let trigger_rotate ~start =
     debug "Trigger task: %s" task_name ;
-    Xapi_periodic_scheduler.add_to_queue task_name
-      (Xapi_periodic_scheduler.Periodic !Xapi_globs.winbind_machine_pwd_timeout)
-      start rotate
+    Scheduler.add_to_queue task_name
+      (Scheduler.Periodic !Xapi_globs.winbind_machine_pwd_timeout) start rotate
 
-  let stop_rotate () = Xapi_periodic_scheduler.remove_from_queue task_name
+  let stop_rotate () = Scheduler.remove_from_queue task_name
 end
 
 let build_netbios_name ~config_params =
diff --git a/ocaml/xapi/helpers.ml b/ocaml/xapi/helpers.ml
index 8c2f91fc2a3..68368754e72 100644
--- a/ocaml/xapi/helpers.ml
+++ b/ocaml/xapi/helpers.ml
@@ -443,8 +443,9 @@ let make_timeboxed_rpc ~__context timeout rpc : Rpc.response =
         in
         List.iter Locking_helpers.kill_resource resources
       in
-      Xapi_periodic_scheduler.add_to_queue (Ref.string_of task_id)
-        Xapi_periodic_scheduler.OneShot timeout cancel ;
+      let module Scheduler = Xapi_stdext_threads_scheduler.Scheduler in
+      Scheduler.add_to_queue (Ref.string_of task_id) Scheduler.OneShot timeout
+        cancel ;
       let transport =
         if Pool_role.is_master () then
           Unix Xapi_globs.unix_domain_socket
@@ -459,7 +460,7 @@ let make_timeboxed_rpc ~__context timeout rpc : Rpc.response =
       let result =
         XMLRPC_protocol.rpc ~srcstr:"xapi" ~dststr:"xapi" ~transport ~http rpc
       in
-      Xapi_periodic_scheduler.remove_from_queue (Ref.string_of task_id) ;
+      Scheduler.remove_from_queue (Ref.string_of task_id) ;
       result
   )
 
diff --git a/ocaml/xapi/pool_periodic_update_sync.ml b/ocaml/xapi/pool_periodic_update_sync.ml
index 45aacf82a9c..a9755d0cf1e 100644
--- a/ocaml/xapi/pool_periodic_update_sync.ml
+++ b/ocaml/xapi/pool_periodic_update_sync.ml
@@ -16,6 +16,7 @@ module D = Debug.Make (struct let name = __MODULE__ end)
 
 open D
 open Client
+module Scheduler = Xapi_stdext_threads_scheduler.Scheduler
 
 type frequency = Daily | Weekly of int
 
@@ -162,12 +163,11 @@ let rec update_sync () =
   )
 
 and add_to_queue ~__context () =
-  let open Xapi_periodic_scheduler in
-  add_to_queue periodic_update_sync_task_name OneShot
+  Scheduler.add_to_queue periodic_update_sync_task_name Scheduler.OneShot
     (seconds_until_next_schedule ~__context)
     update_sync
 
 let set_enabled ~__context ~value =
-  Xapi_periodic_scheduler.remove_from_queue periodic_update_sync_task_name ;
+  Scheduler.remove_from_queue periodic_update_sync_task_name ;
   if value then
     add_to_queue ~__context ()
diff --git a/ocaml/xapi/xapi.ml b/ocaml/xapi/xapi.ml
index ca87e740efb..fd5c0650266 100644
--- a/ocaml/xapi/xapi.ml
+++ b/ocaml/xapi/xapi.ml
@@ -1114,7 +1114,7 @@ let server_init () =
             )
           ; ( "Starting periodic scheduler"
             , [Startup.OnThread]
-            , Xapi_periodic_scheduler.loop
+            , Xapi_stdext_threads_scheduler.Scheduler.loop
             )
           ; ( "Synchronising host configuration files"
             , []
diff --git a/ocaml/xapi/xapi_event.ml b/ocaml/xapi/xapi_event.ml
index 8c7432106ab..600d2859dd3 100644
--- a/ocaml/xapi/xapi_event.ml
+++ b/ocaml/xapi/xapi_event.ml
@@ -425,12 +425,12 @@ module From = struct
           && (not (session_is_invalid call))
           && Unix.gettimeofday () < deadline
         do
-          Xapi_periodic_scheduler.add_to_queue timeoutname
-            Xapi_periodic_scheduler.OneShot
+          Xapi_stdext_threads_scheduler.Scheduler.add_to_queue timeoutname
+            Xapi_stdext_threads_scheduler.Scheduler.OneShot
             (deadline -. Unix.gettimeofday () +. 0.5)
             (fun () -> Condition.broadcast c) ;
           Condition.wait c m ;
-          Xapi_periodic_scheduler.remove_from_queue timeoutname
+          Xapi_stdext_threads_scheduler.Scheduler.remove_from_queue timeoutname
         done
     ) ;
     if session_is_invalid call then (
diff --git a/ocaml/xapi/xapi_host.ml b/ocaml/xapi/xapi_host.ml
index 46e06a9b4d7..cd6ae3a7d35 100644
--- a/ocaml/xapi/xapi_host.ml
+++ b/ocaml/xapi/xapi_host.ml
@@ -938,12 +938,12 @@ let ask_host_if_it_is_a_slave ~__context ~host =
         "ask_host_if_it_is_a_slave: host taking a long time to respond - IP: \
          %s; uuid: %s"
         ip uuid ;
-      Xapi_periodic_scheduler.add_to_queue task_name
-        Xapi_periodic_scheduler.OneShot timeout
+      Xapi_stdext_threads_scheduler.Scheduler.add_to_queue task_name
+        Xapi_stdext_threads_scheduler.Scheduler.OneShot timeout
         (log_host_slow_to_respond (min (2. *. timeout) 300.))
     in
-    Xapi_periodic_scheduler.add_to_queue task_name
-      Xapi_periodic_scheduler.OneShot timeout
+    Xapi_stdext_threads_scheduler.Scheduler.add_to_queue task_name
+      Xapi_stdext_threads_scheduler.Scheduler.OneShot timeout
       (log_host_slow_to_respond timeout) ;
     let res =
       Message_forwarding.do_op_on_localsession_nolivecheck ~local_fn ~__context
@@ -951,7 +951,7 @@ let ask_host_if_it_is_a_slave ~__context ~host =
           Client.Client.Pool.is_slave ~rpc ~session_id ~host
       )
     in
-    Xapi_periodic_scheduler.remove_from_queue task_name ;
+    Xapi_stdext_threads_scheduler.Scheduler.remove_from_queue task_name ;
     res
   in
   Server_helpers.exec_with_subtask ~__context "host.ask_host_if_it_is_a_slave"
@@ -1497,8 +1497,8 @@ let sync_data ~__context ~host = Xapi_sync.sync_host ~__context host
 (* Nb, no attempt to wrap exceptions yet *)
 
 let backup_rrds ~__context ~host:_ ~delay =
-  Xapi_periodic_scheduler.add_to_queue "RRD backup"
-    Xapi_periodic_scheduler.OneShot delay (fun _ ->
+  Xapi_stdext_threads_scheduler.Scheduler.add_to_queue "RRD backup"
+    Xapi_stdext_threads_scheduler.Scheduler.OneShot delay (fun _ ->
       let master_address = Pool_role.get_master_address_opt () in
       log_and_ignore_exn (Rrdd.backup_rrds master_address) ;
       log_and_ignore_exn (fun () ->
diff --git a/ocaml/xapi/xapi_periodic_scheduler_init.ml b/ocaml/xapi/xapi_periodic_scheduler_init.ml
index d74b349e240..39866292460 100644
--- a/ocaml/xapi/xapi_periodic_scheduler_init.ml
+++ b/ocaml/xapi/xapi_periodic_scheduler_init.ml
@@ -76,46 +76,53 @@ let register ~__context =
   let update_all_subjects_delay = 10.0 in
   (* initial delay = 10 seconds *)
   if master then
-    Xapi_periodic_scheduler.add_to_queue "Synchronising RRDs/messages"
-      (Xapi_periodic_scheduler.Periodic sync_timer) sync_delay sync_func ;
+    Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
+      "Synchronising RRDs/messages"
+      (Xapi_stdext_threads_scheduler.Scheduler.Periodic sync_timer) sync_delay
+      sync_func ;
   if master then
-    Xapi_periodic_scheduler.add_to_queue "Backing up RRDs"
-      (Xapi_periodic_scheduler.Periodic rrdbackup_timer) rrdbackup_delay
-      rrdbackup_func ;
+    Xapi_stdext_threads_scheduler.Scheduler.add_to_queue "Backing up RRDs"
+      (Xapi_stdext_threads_scheduler.Scheduler.Periodic rrdbackup_timer)
+      rrdbackup_delay rrdbackup_func ;
   if master then
-    Xapi_periodic_scheduler.add_to_queue
+    Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
       "Revalidating externally-authenticated sessions"
-      (Xapi_periodic_scheduler.Periodic
+      (Xapi_stdext_threads_scheduler.Scheduler.Periodic
          !Xapi_globs.session_revalidation_interval
-      ) session_revalidation_delay session_revalidation_func ;
+      )
+      session_revalidation_delay session_revalidation_func ;
   if master then
-    Xapi_periodic_scheduler.add_to_queue
+    Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
       "Trying to update subjects' info using external directory service (if \
        any)"
-      (Xapi_periodic_scheduler.Periodic !Xapi_globs.update_all_subjects_interval)
+      (Xapi_stdext_threads_scheduler.Scheduler.Periodic
+         !Xapi_globs.update_all_subjects_interval
+      )
       update_all_subjects_delay update_all_subjects_func ;
-  Xapi_periodic_scheduler.add_to_queue "Periodic scheduler heartbeat"
-    (Xapi_periodic_scheduler.Periodic hb_timer) 240.0 hb_func ;
-  Xapi_periodic_scheduler.add_to_queue "Update monitor configuration"
-    (Xapi_periodic_scheduler.Periodic 3600.0) 3600.0
+  Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
+    "Periodic scheduler heartbeat"
+    (Xapi_stdext_threads_scheduler.Scheduler.Periodic hb_timer) 240.0 hb_func ;
+  Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
+    "Update monitor configuration"
+    (Xapi_stdext_threads_scheduler.Scheduler.Periodic 3600.0) 3600.0
     Monitor_master.update_configuration_from_master ;
   ( if master then
       let freq = !Xapi_globs.failed_login_alert_freq |> float_of_int in
-      Xapi_periodic_scheduler.add_to_queue
+      Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
         "Periodic alert failed login attempts"
-        (Xapi_periodic_scheduler.Periodic freq) freq
+        (Xapi_stdext_threads_scheduler.Scheduler.Periodic freq) freq
         Xapi_pool.alert_failed_login_attempts
   ) ;
-  Xapi_periodic_scheduler.add_to_queue "broken_kernel"
-    (Xapi_periodic_scheduler.Periodic 600.) 600. (fun () ->
+  Xapi_stdext_threads_scheduler.Scheduler.add_to_queue "broken_kernel"
+    (Xapi_stdext_threads_scheduler.Scheduler.Periodic 600.) 600. (fun () ->
       Server_helpers.exec_with_new_task
         "Periodic alert if the running kernel is broken in some serious way."
         (fun __context -> Xapi_host.alert_if_kernel_broken ~__context
       )
   ) ;
-  Xapi_periodic_scheduler.add_to_queue
+  Xapi_stdext_threads_scheduler.Scheduler.add_to_queue
     "Period alert if TLS verification emergency disabled"
-    (Xapi_periodic_scheduler.Periodic 600.) 600. (fun () ->
+    (Xapi_stdext_threads_scheduler.Scheduler.Periodic 600.) 600. (fun () ->
       Server_helpers.exec_with_new_task
         "Period alert if TLS verification emergency disabled" (fun __context ->
           Xapi_host.alert_if_tls_verification_was_emergency_disabled ~__context
diff --git a/quality-gate.sh b/quality-gate.sh
index b1d170041f1..b72ca099aa7 100755
--- a/quality-gate.sh
+++ b/quality-gate.sh
@@ -25,7 +25,7 @@ verify-cert () {
 }
 
 mli-files () {
-  N=498
+  N=497
   # do not count ml files from the tests in ocaml/{tests/perftest/quicktest}
   MLIS=$(git ls-files -- '**/*.mli' | grep -vE "ocaml/tests|ocaml/perftest|ocaml/quicktest|ocaml/message-switch/core_test" | xargs -I {} sh -c "echo {} | cut -f 1 -d '.'" \;)
   MLS=$(git  ls-files -- '**/*.ml'  | grep -vE "ocaml/tests|ocaml/perftest|ocaml/quicktest|ocaml/message-switch/core_test" | xargs -I {} sh -c "echo {} | cut -f 1 -d '.'" \;)