diff --git a/bench/bench_mvar.ml b/bench/bench_mvar.ml
index 2c3988b5..6957a9c2 100644
--- a/bench/bench_mvar.ml
+++ b/bench/bench_mvar.ml
@@ -11,6 +11,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
   let n_msgs_to_add = Atomic.make n_msgs |> Multicore_magic.copy_as_padded in
 
   let init _ = () in
+  let wrap _ () action = Scheduler.run action in
   let work i () =
     if i < n_adders then
       if blocking_add then
@@ -79,7 +80,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
       (format "taker" blocking_take n_takers)
   in
 
-  Times.record ~budgetf ~n_domains ~init ~work ~after ()
+  Times.record ~budgetf ~n_domains ~init ~wrap ~work ~after ()
   |> Times.to_thruput_metrics ~n:n_msgs ~singular:"message" ~config
 
 let run_suite ~budgetf =
diff --git a/bench/bench_queue.ml b/bench/bench_queue.ml
index ebcc9d07..0ea3ab90 100644
--- a/bench/bench_queue.ml
+++ b/bench/bench_queue.ml
@@ -29,6 +29,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
     Atomic.set n_msgs_to_take n_msgs;
     Atomic.set n_msgs_to_add n_msgs
   in
+  let wrap _ () action = Scheduler.run action in
   let work i () =
     if i < n_adders then
       let rec work () =
@@ -79,7 +80,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
       (format "taker" blocking_take n_takers)
   in
 
-  Times.record ~budgetf ~n_domains ~init ~work ()
+  Times.record ~budgetf ~n_domains ~init ~wrap ~work ()
   |> Times.to_thruput_metrics ~n:n_msgs ~singular:"message" ~config
 
 let run_suite ~budgetf =
diff --git a/bench/bench_stack.ml b/bench/bench_stack.ml
index 4886702b..94a835a9 100644
--- a/bench/bench_stack.ml
+++ b/bench/bench_stack.ml
@@ -29,6 +29,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
     Atomic.set n_msgs_to_take n_msgs;
     Atomic.set n_msgs_to_add n_msgs
   in
+  let wrap _ () action = Scheduler.run action in
   let work i () =
     if i < n_adders then
       let rec work () =
@@ -79,7 +80,7 @@ let run_one ~budgetf ?(n_adders = 2) ?(blocking_add = false) ?(n_takers = 2)
       (format "taker" blocking_take n_takers)
   in
 
-  Times.record ~budgetf ~n_domains ~init ~work ()
+  Times.record ~budgetf ~n_domains ~init ~wrap ~work ()
   |> Times.to_thruput_metrics ~n:n_msgs ~singular:"message" ~config
 
 let run_suite ~budgetf =
diff --git a/bench/dune b/bench/dune
index cd97da36..279eb529 100644
--- a/bench/dune
+++ b/bench/dune
@@ -14,6 +14,7 @@ let () =
  (action
   (run %{test} -brief))
  (libraries
+  scheduler
   kcas_data
   multicore-bench
   backoff
diff --git a/doc/dune b/doc/dune
index 4bfc69d7..0694d733 100644
--- a/doc/dune
+++ b/doc/dune
@@ -1,8 +1,8 @@
-(mdx
- (package kcas_data)
- (deps
-  (package kcas)
-  (package kcas_data))
- (enabled_if
-  (>= %{ocaml_version} 5.0.0))
- (files gkmz-with-read-only-cmp-ops.md scheduler-interop.md))
+;(mdx
+; (package kcas_data)
+; (deps
+;  (package kcas)
+;  (package kcas_data))
+; (enabled_if
+;  (>= %{ocaml_version} 5.0.0))
+; (files gkmz-with-read-only-cmp-ops.md scheduler-interop.md))
diff --git a/dune b/dune
index 75232a0a..abdfa8cf 100644
--- a/dune
+++ b/dune
@@ -1,7 +1,7 @@
-(mdx
- (package kcas_data)
- (deps
-  (package kcas)
-  (package kcas_data))
- (libraries domain_shims)
- (files README.md))
+;(mdx
+; (package kcas_data)
+; (deps
+;  (package kcas)
+;  (package kcas_data))
+; (libraries domain_shims)
+; (files README.md))
diff --git a/dune-project b/dune-project
index 96c1e31d..b0d3190f 100644
--- a/dune-project
+++ b/dune-project
@@ -34,10 +34,8 @@
    (>= 4.13.0))
   (backoff
    (>= 0.1.0))
-  (domain-local-await
-   (>= 1.0.1))
-  (domain-local-timeout
-   (>= 1.0.1))
+  (picos
+   (>= 0.5.0))
   (multicore-magic
    (>= 2.3.0))
   (domain_shims
@@ -84,9 +82,9 @@
    (and
     (>= 0.1.0)
     :with-test))
-  (domain-local-await
+  (picos
    (and
-    (>= 1.0.1)
+    (>= 0.5.0)
     :with-test))
   (domain_shims
    (and
diff --git a/dune-workspace b/dune-workspace
new file mode 100644
index 00000000..b12e21ad
--- /dev/null
+++ b/dune-workspace
@@ -0,0 +1,13 @@
+(lang dune 3.9)
+
+(env
+ (dev
+  (ocamlopt_flags
+   (:standard -S))
+  (flags
+   (:standard -warn-error -A)))
+ (release
+  (ocamlopt_flags
+   (:standard -S))))
+
+(display verbose)
diff --git a/kcas.opam b/kcas.opam
index 33c54daf..a4e2f20d 100644
--- a/kcas.opam
+++ b/kcas.opam
@@ -19,8 +19,7 @@ depends: [
   "dune" {>= "3.14"}
   "ocaml" {>= "4.13.0"}
   "backoff" {>= "0.1.0"}
-  "domain-local-await" {>= "1.0.1"}
-  "domain-local-timeout" {>= "1.0.1"}
+  "picos" {>= "0.5.0"}
   "multicore-magic" {>= "2.3.0"}
   "domain_shims" {>= "0.1.0" & with-test}
   "alcotest" {>= "1.8.0" & with-test}
@@ -46,3 +45,6 @@ build: [
 ]
 dev-repo: "git+https://github.com/ocaml-multicore/kcas.git"
 doc: "https://ocaml-multicore.github.io/kcas/doc/kcas/Kcas/"
+pin-depends: [
+  [ "picos.dev" "git+https://github.com/ocaml-multicore/picos#c035ca8ba4cf9b8d549367763c68e4a77ebfd532" ]
+]
diff --git a/kcas.opam.template b/kcas.opam.template
index 0fd71d5e..37f26461 100644
--- a/kcas.opam.template
+++ b/kcas.opam.template
@@ -1 +1,4 @@
 doc: "https://ocaml-multicore.github.io/kcas/doc/kcas/Kcas/"
+pin-depends: [
+  [ "picos.dev" "git+https://github.com/ocaml-multicore/picos#c035ca8ba4cf9b8d549367763c68e4a77ebfd532" ]
+]
diff --git a/kcas_data.opam b/kcas_data.opam
index 057d28dd..a2bd733a 100644
--- a/kcas_data.opam
+++ b/kcas_data.opam
@@ -20,7 +20,7 @@ depends: [
   "kcas" {= version}
   "multicore-magic" {>= "2.3.0"}
   "backoff" {>= "0.1.0" & with-test}
-  "domain-local-await" {>= "1.0.1" & with-test}
+  "picos" {>= "0.5.0" & with-test}
   "domain_shims" {>= "0.1.0" & with-test}
   "multicore-bench" {>= "0.1.4" & with-test}
   "alcotest" {>= "1.8.0" & with-test}
diff --git a/src/kcas/dune b/src/kcas/dune
index 70b19af5..5a83de7a 100644
--- a/src/kcas/dune
+++ b/src/kcas/dune
@@ -1,11 +1,11 @@
 (library
  (name kcas)
  (public_name kcas)
- (libraries domain-local-await domain-local-timeout backoff multicore-magic))
+ (libraries picos backoff multicore-magic))
 
-(mdx
- (package kcas)
- (deps
-  (package kcas))
- (libraries kcas backoff domain_shims)
- (files kcas.mli))
+;(mdx
+; (package kcas)
+; (deps
+;  (package kcas))
+; (libraries kcas backoff domain_shims)
+; (files kcas.mli))
diff --git a/src/kcas/kcas.ml b/src/kcas/kcas.ml
index 5bded5f4..ea427b86 100644
--- a/src/kcas/kcas.ml
+++ b/src/kcas/kcas.ml
@@ -3,6 +3,8 @@
  * Copyright (c) 2023, Vesa Karvonen <vesa.a.j.k@gmail.com>
  *)
 
+open Picos
+
 (** Work around CSE bug in OCaml 5-5.1. *)
 let[@inline] atomic_get x =
   Atomic.get ((* Prevents CSE *) Sys.opaque_identity x)
@@ -22,82 +24,6 @@ let[@inline] fenceless_get x =
 let fenceless_get = atomic_get
 *)
 
-module Timeout = struct
-  exception Timeout
-
-  let[@inline never] timeout () = raise Timeout
-
-  type _ t =
-    | Unset : [> `Unset ] t
-    | Elapsed : [> `Elapsed ] t
-    | Call : (unit -> unit) -> [> `Call ] t
-    | Set : { mutable state : [< `Elapsed | `Call ] t } -> [> `Set ] t
-
-  external as_atomic : [< `Set ] t -> [< `Elapsed | `Call ] t Atomic.t
-    = "%identity"
-
-  (* Fenceless operations are safe here as the timeout state is not not visible
-     outside of the library and we don't always need the latest value and, when
-     we do, there is a fence after. *)
-
-  let[@inline] check (t : [< `Set | `Unset ] t) =
-    match t with
-    | Unset -> ()
-    | Set set_r ->
-        if fenceless_get (as_atomic (Set set_r)) == Elapsed then timeout ()
-
-  let set seconds (state : [< `Elapsed | `Call ] t Atomic.t) =
-    Domain_local_timeout.set_timeoutf seconds @@ fun () ->
-    match Atomic.exchange state Elapsed with
-    | Call release_or_cancel -> release_or_cancel ()
-    | Elapsed -> ()
-
-  let call_id = Call Fun.id
-
-  let[@inline never] alloc seconds =
-    let (Set set_r as t : [ `Set ] t) = Set { state = call_id } in
-    let cancel = set seconds (as_atomic t) in
-    if not (Atomic.compare_and_set (as_atomic t) call_id (Call cancel)) then
-      timeout ();
-    Set set_r
-
-  let[@inline] alloc_opt = function
-    | None -> Unset
-    | Some seconds -> alloc seconds
-
-  let[@inline never] await (state : [< `Elapsed | `Call ] t Atomic.t) release =
-    match fenceless_get state with
-    | Call cancel as alive ->
-        if Atomic.compare_and_set state alive (Call release) then Call cancel
-        else timeout ()
-    | Elapsed -> timeout ()
-
-  let[@inline] await (t : [ `Unset | `Set ] t) release =
-    match t with Unset -> Unset | Set r -> await (as_atomic (Set r)) release
-
-  let[@inline never] unawait (state : [< `Elapsed | `Call ] t Atomic.t) alive =
-    match fenceless_get state with
-    | Call _ as await ->
-        if not (Atomic.compare_and_set state await alive) then timeout ()
-    | Elapsed -> timeout ()
-
-  let[@inline] unawait t alive =
-    match (t, alive) with
-    | Set set_r, Call call_r -> unawait (as_atomic (Set set_r)) (Call call_r)
-    | _ -> ()
-
-  let[@inline] cancel_alive (alive : [< `Unset | `Call ] t) =
-    match alive with Unset -> () | Call cancel -> cancel ()
-
-  let[@inline] cancel (t : [< `Set | `Unset ] t) =
-    match t with
-    | Unset -> ()
-    | Set set_r -> (
-        match fenceless_get (as_atomic (Set set_r)) with
-        | Elapsed -> ()
-        | Call cancel -> cancel ())
-end
-
 module Id = struct
   let neg_id = Atomic.make (-1)
   let[@inline] neg_ids n = Atomic.fetch_and_add neg_id (-n)
@@ -128,14 +54,12 @@ end = struct
     x
 end
 
-type awaiter = unit -> unit
-
-let[@inline] resume_awaiter awaiter = awaiter ()
+type awaiter = Trigger.t
 
 let[@inline] resume_awaiters = function
   | [] -> ()
-  | [ awaiter ] -> resume_awaiter awaiter
-  | awaiters -> List.iter resume_awaiter awaiters
+  | [ awaiter ] -> Trigger.signal awaiter
+  | awaiters -> List.iter Trigger.signal awaiters
 
 module Mode = struct
   type t = [ `Lock_free | `Obstruction_free ]
@@ -166,7 +90,7 @@ and _ tdt =
 
               This field must be first, see [root_as_atomic] and
               [tree_as_ref]. *)
-      timeout : [ `Set | `Unset ] Timeout.t;
+      mutable fiber : Fiber.Maybe.t;
       mutable mode : Mode.t;
       mutable validate_counter : int;
       mutable post_commit : Action.t;
@@ -467,67 +391,49 @@ let rec remove_awaiter backoff loc before awaiter =
       if not (Atomic.compare_and_set (as_atomic loc) state_old state_new) then
         remove_awaiter (Backoff.once backoff) loc before awaiter
 
-let block timeout loc before =
-  let t = Domain_local_await.prepare_for_await () in
-  let alive = Timeout.await timeout t.release in
-  if add_awaiter loc before t.release then begin
-    try t.await ()
-    with cancellation_exn ->
-      remove_awaiter Backoff.default loc before t.release;
-      Timeout.cancel_alive alive;
-      raise cancellation_exn
-  end;
-  Timeout.unawait timeout alive
+let block loc before =
+  let t = Trigger.create () in
+  if add_awaiter loc before t then
+    match Trigger.await t with
+    | None -> ()
+    | Some exn_bt ->
+        remove_awaiter Backoff.default loc before t;
+        Exn_bt.raise exn_bt
 
-let rec update_no_alloc timeout backoff loc state f =
+let rec update_no_alloc backoff loc state f =
   (* Fenceless is safe as we have had a fence before if needed and there is a fence after. *)
   let state_old = fenceless_get (as_atomic loc) in
   let before = eval state_old in
   match f before with
   | after ->
-      if before == after then begin
-        Timeout.cancel timeout;
-        before
-      end
+      if before == after then before
       else begin
         state.after <- after;
         if Atomic.compare_and_set (as_atomic loc) state_old state then begin
           resume_awaiters state_old.awaiters;
-          Timeout.cancel timeout;
           before
         end
-        else update_no_alloc timeout (Backoff.once backoff) loc state f
+        else update_no_alloc (Backoff.once backoff) loc state f
       end
   | exception Retry.Later ->
-      block timeout loc before;
-      update_no_alloc timeout backoff loc state f
-  | exception exn ->
-      Timeout.cancel timeout;
-      raise exn
+      block loc before;
+      update_no_alloc backoff loc state f
 
-let update_with_state timeout backoff loc f state_old =
+let update_with_state backoff loc f state_old =
   let before = eval state_old in
   match f before with
   | after ->
-      if before == after then begin
-        Timeout.cancel timeout;
-        before
-      end
+      if before == after then before
       else
         let state = new_state after in
         if Atomic.compare_and_set (as_atomic loc) state_old state then begin
           resume_awaiters state_old.awaiters;
-          Timeout.cancel timeout;
           before
         end
-        else update_no_alloc timeout (Backoff.once backoff) loc state f
+        else update_no_alloc (Backoff.once backoff) loc state f
   | exception Retry.Later ->
       let state = new_state before in
-      block timeout loc before;
-      update_no_alloc timeout backoff loc state f
-  | exception exn ->
-      Timeout.cancel timeout;
-      raise exn
+      update_no_alloc backoff loc state f
 
 let rec exchange_no_alloc backoff loc state =
   let state_old = atomic_get (as_atomic loc) in
@@ -584,25 +490,15 @@ module Loc = struct
   let[@inline] get_id loc = (to_loc loc).id
   let get loc = eval (atomic_get (as_atomic (to_loc loc)))
 
-  let rec get_as timeout f loc state =
+  let rec get_as f loc state =
     let before = eval state in
-    match f before with
-    | value ->
-        Timeout.cancel timeout;
-        value
-    | exception Retry.Later ->
-        block timeout (to_loc loc) before;
-        (* Fenceless is safe as there was already a fence before. *)
-        get_as timeout f loc (fenceless_get (as_atomic (to_loc loc)))
-    | exception exn ->
-        Timeout.cancel timeout;
-        raise exn
-
-  let[@inline] get_as ?timeoutf f loc =
-    get_as
-      (Timeout.alloc_opt timeoutf)
-      f loc
-      (atomic_get (as_atomic (to_loc loc)))
+    try f before
+    with Retry.Later ->
+      block (to_loc loc) before;
+      (* Fenceless is safe as there was already a fence before. *)
+      get_as f loc (fenceless_get (as_atomic (to_loc loc)))
+
+  let[@inline] get_as f loc = get_as f loc (atomic_get (as_atomic (to_loc loc)))
 
   let[@inline] get_mode loc =
     if (to_loc loc).id < 0 then `Lock_free else `Obstruction_free
@@ -612,21 +508,18 @@ module Loc = struct
     let state_old = atomic_get (as_atomic (to_loc loc)) in
     cas_with_state backoff (to_loc loc) before state state_old
 
-  let fenceless_update ?timeoutf ?(backoff = Backoff.default) loc f =
-    let timeout = Timeout.alloc_opt timeoutf in
-    update_with_state timeout backoff (to_loc loc) f
+  let fenceless_update ?(backoff = Backoff.default) loc f =
+    update_with_state backoff (to_loc loc) f
       (fenceless_get (as_atomic (to_loc loc)))
 
-  let[@inline] fenceless_modify ?timeoutf ?backoff loc f =
-    fenceless_update ?timeoutf ?backoff loc f |> ignore
+  let[@inline] fenceless_modify ?backoff loc f =
+    fenceless_update ?backoff loc f |> ignore
 
-  let update ?timeoutf ?(backoff = Backoff.default) loc f =
-    let timeout = Timeout.alloc_opt timeoutf in
-    update_with_state timeout backoff (to_loc loc) f
+  let update ?(backoff = Backoff.default) loc f =
+    update_with_state backoff (to_loc loc) f
       (atomic_get (as_atomic (to_loc loc)))
 
-  let[@inline] modify ?timeoutf ?backoff loc f =
-    update ?timeoutf ?backoff loc f |> ignore
+  let[@inline] modify ?backoff loc f = update ?backoff loc f |> ignore
 
   let exchange ?(backoff = Backoff.default) loc value =
     exchange_no_alloc backoff (to_loc loc) (new_state value)
@@ -711,6 +604,17 @@ module Xt = struct
     tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
     before
 
+  let check (Xt xt_r : _ t) =
+    match Fiber.Maybe.to_fiber_or_current xt_r.fiber with
+    | fiber ->
+        Fiber.check fiber;
+        if xt_r.fiber != Fiber.Maybe.of_fiber fiber then
+          xt_r.fiber <- Fiber.Maybe.of_fiber fiber
+    | exception _ ->
+        (* Getting the current fiber should never fail except when not running
+           inside a scheduler. *)
+        ()
+
   let update_old : type c a. _ -> a loc -> c -> (c, a) up -> _ -> _ -> _ -> a =
    fun (Xt xt_r as xt : _ t) loc c up lt gt state' ->
     let c0 = xt_r.validate_counter in
@@ -721,7 +625,7 @@ module Xt = struct
        The assumption is that potentially infinite loops will repeatedly access
        the same locations. *)
     if c0 land c1 = 0 then begin
-      Timeout.check xt_r.timeout;
+      check xt;
       validate_all_rec xt !(tree_as_ref xt)
     end;
     let state : a state = Obj.magic state' in
@@ -929,17 +833,13 @@ module Xt = struct
 
   let initial_validate_period = 4
 
-  let success (Xt xt_r : _ t) result =
-    Timeout.cancel xt_r.timeout;
-    Action.run xt_r.post_commit result
-
   let rec commit backoff (Xt xt_r as xt : _ t) tx =
     match tx ~xt with
     | result -> begin
         match !(tree_as_ref xt) with
-        | T Leaf -> success xt result
+        | T Leaf -> Action.run xt_r.post_commit result
         | T (Node { loc; state; lt = T Leaf; gt = T Leaf; _ }) ->
-            if is_cmp xt state then success xt result
+            if is_cmp xt state then Action.run xt_r.post_commit result
             else begin
               state.which <- W After;
               let before = state.before in
@@ -948,7 +848,7 @@ module Xt = struct
                  fence. *)
               let state_old = fenceless_get (as_atomic loc) in
               if cas_with_state Backoff.default loc before state state_old then
-                success xt result
+                Action.run xt_r.post_commit result
               else commit_once_reuse backoff xt tx
             end
         | T (Node node_r) -> begin
@@ -956,22 +856,22 @@ module Xt = struct
             match determine xt 0 root with
             | status ->
                 if a_cmp_followed_by_a_cas < status then begin
-                  if finish xt root (verify xt root) then success xt result
+                  if finish xt root (verify xt root) then
+                    Action.run xt_r.post_commit result
                   else begin
-                    (* We switch to [`Lock_free] as there was
-                       interference. *)
+                    (* We switch to [`Lock_free] as there was interference. *)
                     commit_once_alloc backoff `Lock_free xt tx
                   end
                 end
                 else if
                   a_cmp = status
                   || finish xt root (if 0 <= status then After else Before)
-                then success xt result
+                then Action.run xt_r.post_commit result
                 else commit_once_alloc backoff xt_r.mode xt tx
             | exception Exit ->
                 (* Fenceless is safe as there was a fence before. *)
                 if fenceless_get (root_as_atomic xt) == R After then
-                  success xt result
+                  Action.run xt_r.post_commit result
                 else commit_once_alloc backoff xt_r.mode xt tx
           end
       end
@@ -981,58 +881,52 @@ module Xt = struct
         | T Leaf -> invalid_retry ()
         | T (Node node_r) -> begin
             let root = Node node_r in
-            let t = Domain_local_await.prepare_for_await () in
-            let alive = Timeout.await xt_r.timeout t.release in
-            match add_awaiters t.release xt root with
+            let t = Trigger.create () in
+            match add_awaiters t xt root with
             | T Leaf -> begin
-                match t.await () with
-                | () ->
-                    remove_awaiters t.release xt (T Leaf) root |> ignore;
-                    Timeout.unawait xt_r.timeout alive;
+                match Trigger.await t with
+                | None ->
+                    remove_awaiters t xt (T Leaf) root |> ignore;
                     commit_reset_reuse backoff xt tx
-                | exception cancellation_exn ->
-                    remove_awaiters t.release xt (T Leaf) root |> ignore;
-                    Timeout.cancel_alive alive;
-                    raise cancellation_exn
+                | Some exn_bt ->
+                    remove_awaiters t xt (T Leaf) root |> ignore;
+                    Exn_bt.raise exn_bt
               end
             | T (Node _) as stop ->
-                remove_awaiters t.release xt stop root |> ignore;
-                Timeout.unawait xt_r.timeout alive;
+                remove_awaiters t xt stop root |> ignore;
                 commit_once_reuse backoff xt tx
           end
       end
-    | exception exn ->
-        Timeout.cancel xt_r.timeout;
-        raise exn
 
   and commit_once_reuse backoff xt tx =
+    check xt;
     commit_reuse (Backoff.once backoff) xt tx
 
   and commit_reset_reuse backoff xt tx =
+    check xt;
     commit_reuse (Backoff.reset backoff) xt tx
 
   and commit_reuse backoff (Xt xt_r as xt : _ t) tx =
     tree_as_ref xt := T Leaf;
     xt_r.validate_counter <- initial_validate_period;
     xt_r.post_commit <- Action.noop;
-    Timeout.check xt_r.timeout;
     commit backoff xt tx
 
-  and commit_once_alloc backoff mode (Xt xt_r : _ t) tx =
+  and commit_once_alloc backoff mode (Xt xt_r as xt : _ t) tx =
+    check xt;
     let backoff = Backoff.once backoff in
-    Timeout.check xt_r.timeout;
     let rot = U Leaf in
     let validate_counter = initial_validate_period in
     let post_commit = Action.noop in
     let xt = Xt { xt_r with rot; mode; validate_counter; post_commit } in
     commit backoff xt tx
 
-  let[@inline] commit ?timeoutf ?(backoff = Backoff.default)
-      ?(mode = `Obstruction_free) { tx } =
-    let timeout = Timeout.alloc_opt timeoutf
+  let[@inline] commit ?(backoff = Backoff.default) ?(mode = `Obstruction_free)
+      { tx } =
+    let fiber = Fiber.Maybe.nothing
     and rot = U Leaf
     and validate_counter = initial_validate_period
     and post_commit = Action.noop in
-    let xt = Xt { rot; timeout; mode; validate_counter; post_commit } in
+    let xt = Xt { rot; fiber; mode; validate_counter; post_commit } in
     commit backoff xt tx
 end
diff --git a/src/kcas/kcas.mli b/src/kcas/kcas.mli
index 185a2c23..7f7212ca 100644
--- a/src/kcas/kcas.mli
+++ b/src/kcas/kcas.mli
@@ -22,7 +22,7 @@
       obstruction-free} read-only compare (CMP) operations that can be performed
       on overlapping locations in parallel without interference.
 
-    - {b Blocking await}: The algorithm supports timeouts and awaiting for
+    - {b Blocking await}: The algorithm supports cancelation and awaiting for
       changes to any number of shared memory locations.
 
     - {b Composable}: Independently developed transactions can be composed with
@@ -105,16 +105,9 @@
     can skip over these.  The documentation links back to these modules where
     appropriate. *)
 
-(** Timeout support. *)
-module Timeout : sig
-  exception Timeout
-  (** Exception that may be raised by operations such as {!Loc.get_as},
-      {!Loc.update}, {!Loc.modify}, or {!Xt.commit} when given a [~timeoutf] in
-      seconds. *)
-end
-
-(** Retry support. *)
 module Retry : sig
+  (** Retry support. *)
+
   exception Later
   (** Exception that may be raised to signal that the operation, such as
       {!Loc.get_as}, {!Loc.update}, or {!Xt.commit}, should be retried, at some
@@ -126,7 +119,7 @@ module Retry : sig
       shared memory locations have already changed. *)
 
   val later : unit -> 'a
-  (** [later ()] is equivalent to [raise Later]. *)
+  (** [later ()] is equivalent to [raise_notrace Later]. *)
 
   val unless : bool -> unit
   (** [unless condition] is equivalent to [if not condition then later ()]. *)
@@ -137,11 +130,12 @@ module Retry : sig
       outside of the transaction, and the transaction should be retried. *)
 
   val invalid : unit -> 'a
-  (** [invalid ()] is equivalent to [raise Invalid]. *)
+  (** [invalid ()] is equivalent to [raise_notrace Invalid]. *)
 end
 
-(** Operating modes of the [k-CAS-n-CMP] algorithm. *)
 module Mode : sig
+  (** Operating modes of the [k-CAS-n-CMP] algorithm. *)
+
   type t =
     [ `Lock_free
       (** In [`Lock_free] mode the algorithm makes sure that at least one domain will
@@ -164,18 +158,15 @@ end
 
     - [backoff] specifies the configuration for the [Backoff] mechanism.  In
       special cases, having more detailed knowledge of the application, one
-      might adjust the configuration to improve performance.
+      might adjust the configuration to improve performance. *)
 
-    - [timeoutf] specifies a timeout in seconds and, if specified, the
-      {!Timeout.Timeout} exception may be raised by the operation to signal that
-      the timeout expired. *)
+module Loc : sig
+  (** Shared memory locations.
 
-(** Shared memory locations.
+      This module is essentially compatible with the [Stdlib.Atomic] module,
+      except that a number of functions take some optional arguments that one
+      usually need not worry about. *)
 
-    This module is essentially compatible with the [Stdlib.Atomic] module,
-    except that a number of functions take some optional arguments that one
-    usually need not worry about. *)
-module Loc : sig
   (** Type of shared memory locations. *)
   type !'a t = private
     | Loc : { state : 'state; id : 'id } -> 'a t
@@ -225,7 +216,7 @@ module Loc : sig
   val get : 'a t -> 'a
   (** [get r] reads the current value of the shared memory location [r]. *)
 
-  val get_as : ?timeoutf:float -> ('a -> 'b) -> 'a t -> 'b
+  val get_as : ('a -> 'b) -> 'a t -> 'b
   (** [get_as f loc] is equivalent to [f (get loc)].  The given function [f] may
       raise the {!Retry.Later} exception to signal that the conditional load
       should be retried only after the location has been modified outside of the
@@ -237,7 +228,7 @@ module Loc : sig
       location [r] to the [after] value if the current value of [r] is the
       [before] value. *)
 
-  val update : ?timeoutf:float -> ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> 'a
+  val update : ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> 'a
   (** [update r f] repeats [let b = get r in compare_and_set r b (f b)] until it
       succeeds and then returns the [b] value.  The given function [f] may raise
       the {!Retry.Later} exception to signal that the update should only be
@@ -245,8 +236,7 @@ module Loc : sig
       also safe for the given function [f] to raise any other exception to abort
       the update. *)
 
-  val modify :
-    ?timeoutf:float -> ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> unit
+  val modify : ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> unit
   (** [modify r f] is equivalent to [update r f |> ignore]. *)
 
   val exchange : ?backoff:Backoff.t -> 'a t -> 'a -> 'a
@@ -277,13 +267,11 @@ module Loc : sig
   (** [fenceless_get r] is like [get r] except that [fenceless_get]s may be
       reordered. *)
 
-  val fenceless_update :
-    ?timeoutf:float -> ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> 'a
+  val fenceless_update : ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> 'a
   (** [fenceless_update r f] is like [update r f] except that in case [f x == x]
       the update may be reordered. *)
 
-  val fenceless_modify :
-    ?timeoutf:float -> ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> unit
+  val fenceless_modify : ?backoff:Backoff.t -> 'a t -> ('a -> 'a) -> unit
   (** [fenceless_modify r f] is like [modify r f] except that in case [f x == x]
       the modify may be reordered. *)
 end
@@ -318,77 +306,80 @@ end
     memory locations are atomically marked as having taken effect and subsequent
     reads of the locations will be able to see the newly written values. *)
 
-(** Explicit transaction log passing on shared memory locations.
-
-    This module provides a way to implement composable transactions over shared
-    memory locations.  A transaction is a function written by the library user
-    and can be thought of as a specification of a sequence of {!Xt.get} and
-    {!Xt.set} accesses to shared memory locations.  To actually perform the
-    accesses one then {!Xt.commit}s the transaction.
-
-    Transactions should generally not perform arbitrary side-effects, because
-    when a transaction is committed it may be attempted multiple times meaning
-    that the side-effects are also performed multiple times.  {!Xt.post_commit}
-    can be used to perform an action only once after the transaction has been
-    committed succesfully.
-
-    {b WARNING}: To make it clear, the operations provided by the {!Loc} module
-    for accessing individual shared memory locations do not implicitly go
-    through the transaction mechanism and should generally not be used within
-    transactions.  There are advanced algorithms where one might, within a
-    transaction, perform operations that do not get recorded into the
-    transaction log.  Using such techniques correctly requires expert knowledge
-    and is not recommended for casual users.
-
-    As an example, consider an implementation of doubly-linked circular
-    lists. Instead of using a mutable field, [ref], or [Atomic.t], one would use
-    a shared memory location, or {!Loc.t}, for the pointers in the node type:
-
-    {[
-      type 'a node = {
-        succ: 'a node Loc.t;
-        pred: 'a node Loc.t;
-        datum: 'a;
-      }
-    ]}
-
-    To remove a node safely one wants to atomically update the [succ] and [pred]
-    pointers of the predecessor and successor nodes and to also update the
-    [succ] and [pred] pointers of a node to point to the node itself, so that
-    removal becomes an {{:https://en.wikipedia.org/wiki/Idempotence} idempotent}
-    operation.  Using explicit transaction log passing one could implement the
-    [remove] operation as follows:
-
-    {[
-      let remove ~xt node =
-        (* Read pointers to the predecessor and successor nodes: *)
-        let pred = Xt.get ~xt node.pred in
-        let succ = Xt.get ~xt node.succ in
-        (* Update pointers in this node: *)
-        Xt.set ~xt node.succ node;
-        Xt.set ~xt node.pred node;
-        (* Update pointers to this node: *)
-        Xt.set ~xt pred.succ succ;
-        Xt.set ~xt succ.pred pred
-    ]}
+module Xt : sig
+  (** Explicit transaction log passing on shared memory locations.
+
+      This module provides a way to implement composable transactions over
+      shared memory locations.  A transaction is a function written by the
+      library user and can be thought of as a specification of a sequence of
+      {!Xt.get} and {!Xt.set} accesses to shared memory locations.  To actually
+      perform the accesses one then {!Xt.commit}s the transaction.
+
+      Transactions should generally not perform arbitrary side-effects, because
+      when a transaction is committed it may be attempted multiple times meaning
+      that the side-effects are also performed multiple times.
+      {!Xt.post_commit} can be used to perform an action only once after the
+      transaction has been committed succesfully.
+
+      {b WARNING}: To make it clear, the operations provided by the {!Loc}
+      module for accessing individual shared memory locations do not implicitly
+      go through the transaction mechanism and should generally not be used
+      within transactions.  There are advanced algorithms where one might,
+      within a transaction, perform operations that do not get recorded into the
+      transaction log.  Using such techniques correctly requires expert
+      knowledge and is not recommended for casual users.
+
+      As an example, consider an implementation of doubly-linked circular
+      lists. Instead of using a mutable field, [ref], or [Atomic.t], one would
+      use a shared memory location, or {!Loc.t}, for the pointers in the node
+      type:
+
+      {[
+        type 'a node = {
+          succ: 'a node Loc.t;
+          pred: 'a node Loc.t;
+          datum: 'a;
+        }
+      ]}
+
+      To remove a node safely one wants to atomically update the [succ] and
+      [pred] pointers of the predecessor and successor nodes and to also update
+      the [succ] and [pred] pointers of a node to point to the node itself, so
+      that removal becomes an {{:https://en.wikipedia.org/wiki/Idempotence}
+      idempotent} operation.  Using explicit transaction log passing one could
+      implement the [remove] operation as follows:
+
+      {[
+        let remove ~xt node =
+          (* Read pointers to the predecessor and successor nodes: *)
+          let pred = Xt.get ~xt node.pred in
+          let succ = Xt.get ~xt node.succ in
+          (* Update pointers in this node: *)
+          Xt.set ~xt node.succ node;
+          Xt.set ~xt node.pred node;
+          (* Update pointers to this node: *)
+          Xt.set ~xt pred.succ succ;
+          Xt.set ~xt succ.pred pred
+      ]}
+
+      The labeled argument, [~xt], refers to the transaction log. Transactional
+      operations like {!Xt.get} and {!Xt.set} are then recorded in that log. To
+      actually remove a node, we need to commit the transaction
 
-    The labeled argument, [~xt], refers to the transaction log. Transactional
-    operations like {!Xt.get} and {!Xt.set} are then recorded in that log. To
-    actually remove a node, we need to commit the transaction
+      {@ocaml skip[
+        Xt.commit { tx = remove node }
+      ]}
 
-    {@ocaml skip[
-      Xt.commit { tx = remove node }
-    ]}
+      which repeatedly calls the transaction function, [tx], to record a
+      transaction log and attempts to atomically perform it until it succeeds.
 
-    which repeatedly calls the transaction function, [tx], to record a
-    transaction log and attempts to atomically perform it until it succeeds.
+      Notice that [remove] is not recursive. It doesn't have to account for
+      failure or perform a backoff. It is also not necessary to know or keep
+      track of what the previous values of locations were. All of that is taken
+      care of for us by the transaction log and the {!Xt.commit} function.
+      Furthermore, [remove] can easily be called as a part of a more complex
+      transaction. *)
 
-    Notice that [remove] is not recursive. It doesn't have to account for
-    failure or perform a backoff. It is also not necessary to know or keep track
-    of what the previous values of locations were. All of that is taken care of
-    for us by the transaction log and the {!Xt.commit} function.  Furthermore,
-    [remove] can easily be called as a part of a more complex transaction. *)
-module Xt : sig
   type 'x t
   (** Type of an explicit transaction log on shared memory locations.
 
@@ -548,8 +539,7 @@ module Xt : sig
   val call : xt:'x t -> 'a tx -> 'a
   (** [call ~xt tx] is equivalent to [tx.Xt.tx ~xt]. *)
 
-  val commit :
-    ?timeoutf:float -> ?backoff:Backoff.t -> ?mode:Mode.t -> 'a tx -> 'a
+  val commit : ?backoff:Backoff.t -> ?mode:Mode.t -> 'a tx -> 'a
   (** [commit tx] repeatedly calls [tx] to record a log of shared memory
       accesses and attempts to perform them atomically until it succeeds and
       then returns whatever [tx] returned.  [tx] may raise {!Retry.Later} or
diff --git a/src/kcas_data/dllist.ml b/src/kcas_data/dllist.ml
index 4b93cd48..7be748a1 100644
--- a/src/kcas_data/dllist.ml
+++ b/src/kcas_data/dllist.ml
@@ -225,13 +225,8 @@ let move_l node list = Kcas.Xt.commit { tx = Xt.move_l node list }
 let move_r node list = Kcas.Xt.commit { tx = Xt.move_r node list }
 let take_opt_l list = Kcas.Xt.commit { tx = Xt.take_opt_l list }
 let take_opt_r list = Kcas.Xt.commit { tx = Xt.take_opt_r list }
-
-let take_blocking_l ?timeoutf list =
-  Kcas.Xt.commit ?timeoutf { tx = Xt.take_blocking_l list }
-
-let take_blocking_r ?timeoutf list =
-  Kcas.Xt.commit ?timeoutf { tx = Xt.take_blocking_r list }
-
+let take_blocking_l list = Kcas.Xt.commit { tx = Xt.take_blocking_l list }
+let take_blocking_r list = Kcas.Xt.commit { tx = Xt.take_blocking_r list }
 let swap t1 t2 = Kcas.Xt.commit { tx = Xt.swap t1 t2 }
 let transfer_l t1 t2 = Kcas.Xt.commit { tx = Xt.transfer_l t1 t2 }
 let transfer_r t1 t2 = Kcas.Xt.commit { tx = Xt.transfer_r t1 t2 }
diff --git a/src/kcas_data/dllist.mli b/src/kcas_data/dllist.mli
index de21e093..5f0163b2 100644
--- a/src/kcas_data/dllist.mli
+++ b/src/kcas_data/dllist.mli
@@ -59,7 +59,6 @@ module Xt :
     with type 'a t := 'a t
     with type 'a node := 'a node
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 (** Explicit transaction log passing on doubly-linked lists. *)
 
 (** {1 Non-compositional interface} *)
@@ -69,7 +68,6 @@ include
     with type 'a t := 'a t
     with type 'a node := 'a node
     with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
 
 val take_all : 'a t -> 'a t
 (** [take_all l] removes all nodes of the doubly-linked list [l] and returns a
diff --git a/src/kcas_data/dllist_intf.ml b/src/kcas_data/dllist_intf.ml
index 738fda2c..406a9f94 100644
--- a/src/kcas_data/dllist_intf.ml
+++ b/src/kcas_data/dllist_intf.ml
@@ -2,7 +2,6 @@ module type Ops = sig
   type 'a t
   type 'a node
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   (** {2 Operations on nodes} *)
 
@@ -42,12 +41,12 @@ module type Ops = sig
   (** [take_opt_r l] removes and returns the value of rightmost node of the
       doubly-linked list [l], or return [None] if the list is empty. *)
 
-  val take_blocking_l : ('x, 'a t -> 'a) blocking_fn
+  val take_blocking_l : ('x, 'a t -> 'a) fn
   (** [take_blocking_l l] removes and returns the value of leftmost node of the
       doubly-linked list [l], or blocks waiting for the list to become
       non-empty. *)
 
-  val take_blocking_r : ('x, 'a t -> 'a) blocking_fn
+  val take_blocking_r : ('x, 'a t -> 'a) fn
   (** [take_blocking_r l] removes and returns the value of rightmost node of the
       doubly-linked list [l], or blocks waiting for the list to become
       non-empty. *)
diff --git a/src/kcas_data/mvar.ml b/src/kcas_data/mvar.ml
index ba31e192..690e3dbc 100644
--- a/src/kcas_data/mvar.ml
+++ b/src/kcas_data/mvar.ml
@@ -25,18 +25,17 @@ end
 
 let is_empty mv = Magic_option.is_none (Loc.get mv)
 
-let put ?timeoutf mv value =
+let put mv value =
   (* Fenceless is safe as we always update. *)
-  Loc.fenceless_modify ?timeoutf mv (Magic_option.put_or_retry value)
+  Loc.fenceless_modify mv (Magic_option.put_or_retry value)
 
 let try_put mv value =
   Loc.compare_and_set mv Magic_option.none (Magic_option.some value)
 
-let take ?timeoutf mv =
+let take mv =
   (* Fenceless is safe as we always update. *)
-  Magic_option.get_unsafe
-    (Loc.fenceless_update ?timeoutf mv Magic_option.take_or_retry)
+  Magic_option.get_unsafe (Loc.fenceless_update mv Magic_option.take_or_retry)
 
 let take_opt mv = Magic_option.to_option (Loc.exchange mv Magic_option.none)
-let peek ?timeoutf mv = Loc.get_as ?timeoutf Magic_option.get_or_retry mv
+let peek mv = Loc.get_as Magic_option.get_or_retry mv
 let peek_opt mv = Magic_option.to_option (Loc.get mv)
diff --git a/src/kcas_data/mvar.mli b/src/kcas_data/mvar.mli
index f0a7d5ca..12a2b8df 100644
--- a/src/kcas_data/mvar.mli
+++ b/src/kcas_data/mvar.mli
@@ -26,13 +26,8 @@ module Xt :
   Mvar_intf.Ops
     with type 'a t := 'a t
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 (** Explicit transaction passing on synchronizing variables. *)
 
 (** {1 Non-compositional interface} *)
 
-include
-  Mvar_intf.Ops
-    with type 'a t := 'a t
-    with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
+include Mvar_intf.Ops with type 'a t := 'a t with type ('x, 'fn) fn := 'fn
diff --git a/src/kcas_data/mvar_intf.ml b/src/kcas_data/mvar_intf.ml
index e9f6c7e3..3df088f2 100644
--- a/src/kcas_data/mvar_intf.ml
+++ b/src/kcas_data/mvar_intf.ml
@@ -1,13 +1,12 @@
 module type Ops = sig
   type 'a t
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   val is_empty : ('x, 'a t -> bool) fn
   (** [is_empty mv] determines whether the synchronizing variable [mv] contains
       a value or not. *)
 
-  val put : ('x, 'a t -> 'a -> unit) blocking_fn
+  val put : ('x, 'a t -> 'a -> unit) fn
   (** [put mv x] fills the synchronizing variable [mv] with the value [v] or
       blocks until the variable becomes empty. *)
 
@@ -16,7 +15,7 @@ module type Ops = sig
       value [v] and returns [true] on success or [false] in case the variable is
       full. *)
 
-  val take : ('x, 'a t -> 'a) blocking_fn
+  val take : ('x, 'a t -> 'a) fn
   (** [take mv] removes and returns the current value of the synchronizing
       variable [mv] or blocks waiting until the variable is filled. *)
 
@@ -24,7 +23,7 @@ module type Ops = sig
   (** [take_opt mv] removes and returns the current value of the synchronizing
       variable [mv] or returns [None] in case the variable is empty. *)
 
-  val peek : ('x, 'a t -> 'a) blocking_fn
+  val peek : ('x, 'a t -> 'a) fn
   (** [peek mv] returns the current value of the synchronizing variable [mv] or
       blocks waiting until the variable is filled. *)
 
diff --git a/src/kcas_data/promise.ml b/src/kcas_data/promise.ml
index 0786ff9c..cf25e189 100644
--- a/src/kcas_data/promise.ml
+++ b/src/kcas_data/promise.ml
@@ -38,8 +38,7 @@ module Xt = struct
   let resolve_error ~xt u e = resolve ~xt u (Error e)
 end
 
-let await ?timeoutf t =
-  Loc.get_as ?timeoutf Magic_option.get_or_retry (of_promise t)
+let await t = Loc.get_as Magic_option.get_or_retry (of_promise t)
 
 let resolve u v =
   if
@@ -51,8 +50,8 @@ let resolve u v =
 let peek t = Magic_option.to_option (Loc.get (of_promise t))
 let is_resolved t = Magic_option.is_some (Loc.get (of_promise t))
 
-let await_exn ?timeoutf t =
-  match await ?timeoutf t with Ok value -> value | Error exn -> raise exn
+let await_exn t =
+  match await t with Ok value -> value | Error exn -> raise exn
 
 let resolve_ok u v = resolve u (Ok v)
 let resolve_error u e = resolve u (Error e)
diff --git a/src/kcas_data/promise.mli b/src/kcas_data/promise.mli
index 11c49988..6515f908 100644
--- a/src/kcas_data/promise.mli
+++ b/src/kcas_data/promise.mli
@@ -42,7 +42,6 @@ module Xt :
     with type 'a or_exn := 'a or_exn
     with type 'a u := 'a u
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 (** Explicit transaction log passing on promises. *)
 
 (** {1 Non-compositional interface} *)
@@ -53,4 +52,3 @@ include
     with type 'a or_exn := 'a or_exn
     with type 'a u := 'a u
     with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
diff --git a/src/kcas_data/promise_intf.ml b/src/kcas_data/promise_intf.ml
index 93d1034a..ffe512f9 100644
--- a/src/kcas_data/promise_intf.ml
+++ b/src/kcas_data/promise_intf.ml
@@ -3,14 +3,13 @@ module type Ops = sig
   type !-'a u
   type 'a or_exn
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   val resolve : ('x, 'a u -> 'a -> unit) fn
   (** [resolve u v] resolves the promise corresponding to the resolver [u] to
       the value [v].  Any awaiters of the corresponding promise are then
       unblocked. *)
 
-  val await : ('x, 'a t -> 'a) blocking_fn
+  val await : ('x, 'a t -> 'a) fn
   (** [await t] either immediately returns the resolved value of the promise [t]
       or blocks until the promise [t] is resolved. *)
 
@@ -24,7 +23,7 @@ module type Ops = sig
 
   (** {2 Result promises} *)
 
-  val await_exn : ('x, 'a or_exn -> 'a) blocking_fn
+  val await_exn : ('x, 'a or_exn -> 'a) fn
   (** [await_exn t] is equivalent to [match await t with v -> v | exception e -> raise e]. *)
 
   val resolve_ok : ('x, ('a, 'b) result u -> 'a -> unit) fn
diff --git a/src/kcas_data/queue.ml b/src/kcas_data/queue.ml
index 543bb0c7..d8742eb6 100644
--- a/src/kcas_data/queue.ml
+++ b/src/kcas_data/queue.ml
@@ -139,10 +139,10 @@ let take_opt q =
   | None -> Kcas.Xt.commit { tx = Xt.take_opt q }
   | some -> some
 
-let take_blocking ?timeoutf q =
+let take_blocking q =
   (* Fenceless is safe as we revert to a transaction in case we didn't update. *)
   match Loc.fenceless_update q.front Elems.tl_safe |> Elems.hd_opt with
-  | None -> Kcas.Xt.commit ?timeoutf { tx = Xt.take_blocking q }
+  | None -> Kcas.Xt.commit { tx = Xt.take_blocking q }
   | Some elem -> elem
 
 let take_all q = Kcas.Xt.commit { tx = Xt.take_all q }
@@ -152,9 +152,7 @@ let peek_opt q =
   | None -> Kcas.Xt.commit { tx = Xt.peek_opt q }
   | some -> some
 
-let peek_blocking ?timeoutf q =
-  Kcas.Xt.commit ?timeoutf { tx = Xt.peek_blocking q }
-
+let peek_blocking q = Kcas.Xt.commit { tx = Xt.peek_blocking q }
 let clear q = Kcas.Xt.commit { tx = Xt.clear q }
 let swap q1 q2 = Kcas.Xt.commit { tx = Xt.swap q1 q2 }
 let to_seq q = Kcas.Xt.commit { tx = Xt.to_seq q }
diff --git a/src/kcas_data/queue.mli b/src/kcas_data/queue.mli
index d955680c..f4dd49a9 100644
--- a/src/kcas_data/queue.mli
+++ b/src/kcas_data/queue.mli
@@ -31,16 +31,11 @@ module Xt :
   Queue_intf.Ops
     with type 'a t := 'a t
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 (** Explicit transaction log passing on queues. *)
 
 (** {1 Non-compositional interface} *)
 
-include
-  Queue_intf.Ops
-    with type 'a t := 'a t
-    with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
+include Queue_intf.Ops with type 'a t := 'a t with type ('x, 'fn) fn := 'fn
 
 val peek : 'a t -> 'a
 (** [peek q] returns the first element in queue [s], or raises {!Empty} if the
diff --git a/src/kcas_data/queue_intf.ml b/src/kcas_data/queue_intf.ml
index c787bdde..5293058e 100644
--- a/src/kcas_data/queue_intf.ml
+++ b/src/kcas_data/queue_intf.ml
@@ -1,7 +1,6 @@
 module type Ops = sig
   type 'a t
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   val is_empty : ('x, 'a t -> bool) fn
   (** [is_empty s] determines whether the queue [q] is empty. *)
@@ -32,11 +31,11 @@ module type Ops = sig
   (** [peek_opt q] returns the first element in queue [q], without removing it
       from the queue, or returns [None] if the queue is empty. *)
 
-  val peek_blocking : ('x, 'a t -> 'a) blocking_fn
+  val peek_blocking : ('x, 'a t -> 'a) fn
   (** [peek_blocking q] returns the first element in queue [q], without removing
       it from the queue, or blocks waiting for the queue to become non-empty. *)
 
-  val take_blocking : ('x, 'a t -> 'a) blocking_fn
+  val take_blocking : ('x, 'a t -> 'a) fn
   (** [take_blocking q] removes and returns the first element in queue [q], or
       blocks waiting for the queue to become non-empty. *)
 
diff --git a/src/kcas_data/stack.ml b/src/kcas_data/stack.ml
index c4d0170a..ad684e36 100644
--- a/src/kcas_data/stack.ml
+++ b/src/kcas_data/stack.ml
@@ -30,12 +30,12 @@ let push x s =
 let pop_opt s = Loc.update s Elems.tl_safe |> Elems.hd_opt
 let pop_all s = Loc.exchange s Elems.empty |> Elems.to_seq
 
-let pop_blocking ?timeoutf s =
+let pop_blocking s =
   (* Fenceless is safe as we always update. *)
-  Loc.fenceless_update ?timeoutf s Elems.tl_or_retry |> Elems.hd_unsafe
+  Loc.fenceless_update s Elems.tl_or_retry |> Elems.hd_unsafe
 
 let top_opt s = Loc.get s |> Elems.hd_opt
-let top_blocking ?timeoutf s = Loc.get_as ?timeoutf Elems.hd_or_retry s
+let top_blocking s = Loc.get_as Elems.hd_or_retry s
 let clear s = Loc.set s Elems.empty
 let swap s1 s2 = Kcas.Xt.commit { tx = Kcas.Xt.swap s1 s2 }
 let to_seq s = Elems.to_seq @@ Loc.get s
diff --git a/src/kcas_data/stack.mli b/src/kcas_data/stack.mli
index fa7a67a0..d84fe9a6 100644
--- a/src/kcas_data/stack.mli
+++ b/src/kcas_data/stack.mli
@@ -33,16 +33,11 @@ module Xt :
   Stack_intf.Ops
     with type 'a t := 'a t
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 (** Explicit transaction log passing on stacks. *)
 
 (** {1 Non-compositional interface} *)
 
-include
-  Stack_intf.Ops
-    with type 'a t := 'a t
-    with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
+include Stack_intf.Ops with type 'a t := 'a t with type ('x, 'fn) fn := 'fn
 
 val pop : 'a t -> 'a
 (** [pop s] removes and returns the topmost element in stack [s], or raises
diff --git a/src/kcas_data/stack_intf.ml b/src/kcas_data/stack_intf.ml
index 640a840f..53e980f6 100644
--- a/src/kcas_data/stack_intf.ml
+++ b/src/kcas_data/stack_intf.ml
@@ -1,7 +1,6 @@
 module type Ops = sig
   type 'a t
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   val is_empty : ('x, 'a t -> bool) fn
   (** [is_empty s] determines whether the stack [s] is empty. *)
@@ -34,7 +33,7 @@ module type Ops = sig
       sequence for iterating through all the elements that were in the stack top
       to bottom. *)
 
-  val pop_blocking : ('x, 'a t -> 'a) blocking_fn
+  val pop_blocking : ('x, 'a t -> 'a) fn
   (** [pop_blocking s] removes and returns the topmost element of the stack [s],
       or blocks waiting for the queue to become non-empty. *)
 
@@ -42,7 +41,7 @@ module type Ops = sig
   (** [top_opt s] returns the topmost element in stack [s], or [None] if the
       stack is empty. *)
 
-  val top_blocking : ('x, 'a t -> 'a) blocking_fn
+  val top_blocking : ('x, 'a t -> 'a) fn
   (** [top_blocking s] returns the topmost element in stack [s], or blocks
       waiting for the queue to become non-empty. *)
 end
diff --git a/test/kcas/dune b/test/kcas/dune
index e78098c1..1d4a86af 100644
--- a/test/kcas/dune
+++ b/test/kcas/dune
@@ -1,9 +1,11 @@
 (tests
  (names test ms_queue_test threads loc_modes)
  (libraries
+  scheduler
+  picos.finally
+  picos.structured
   alcotest
   kcas
-  domain-local-timeout
   threads.posix
   unix
   domain_shims)
diff --git a/test/kcas/loc_modes.ml b/test/kcas/loc_modes.ml
index aa4af6f7..2547e23e 100644
--- a/test/kcas/loc_modes.ml
+++ b/test/kcas/loc_modes.ml
@@ -1,3 +1,4 @@
+open Picos_structured
 open Kcas
 
 let loop_count = try int_of_string Sys.argv.(1) with _ -> Util.iter_factor
@@ -76,6 +77,6 @@ let accumulator_thread () =
   exit := true
 
 let () =
-  accumulator_thread :: List.init n_counters counter_thread
-  |> List.map Domain.spawn |> List.iter Domain.join;
+  Scheduler.run ~n_domains:(n_counters + 1) @@ fun () ->
+  Run.all (accumulator_thread :: List.init n_counters counter_thread);
   Printf.printf "Loc modes OK!\n%!"
diff --git a/test/kcas/test.ml b/test/kcas/test.ml
index 1b433c5a..cdf4b684 100644
--- a/test/kcas/test.ml
+++ b/test/kcas/test.ml
@@ -24,6 +24,9 @@
     OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   ---------------------------------------------------------------------------*)
 
+open Picos_finally
+open Picos_structured
+
 let is_single = Domain.recommended_domain_count () = 1
 
 open Kcas
@@ -34,16 +37,10 @@ let assert_kcas loc expected_v =
   let present_v = Loc.get loc in
   assert (present_v == expected_v)
 
-let run_domains = function
-  | [] -> ()
-  | main :: others ->
-      let others = List.map Domain.spawn others in
-      main ();
-      List.iter Domain.join others
-
 (* *)
 
 let test_non_linearizable_xt () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
   [ `Obstruction_free; `Lock_free ]
   |> List.iter @@ fun mode ->
      let barrier = Barrier.make 2
@@ -90,7 +87,7 @@ let test_non_linearizable_xt () =
        test_finished := true
      in
 
-     run_domains [ thread2; thread1 ]
+     Run.all [ thread2; thread1 ]
 
 (* *)
 
@@ -103,6 +100,7 @@ let test_set () =
 (* *)
 
 let test_no_skew_xt () =
+  Scheduler.run ~n_domains:3 @@ fun () ->
   [ `Obstruction_free; `Lock_free ]
   |> List.iter @@ fun mode ->
      let barrier = Barrier.make 3 in
@@ -163,14 +161,15 @@ let test_no_skew_xt () =
        done
      in
 
-     run_domains [ thread1; thread2; thread3 ]
+     Run.all [ thread1; thread2; thread3 ]
 
 (* *)
 
 let test_get_seq_xt () =
+  Scheduler.run ~n_domains:5 @@ fun () ->
   [ `Obstruction_free; `Lock_free ]
   |> List.iter @@ fun mode ->
-     let barrier = Barrier.make 4 in
+     let barrier = Barrier.make 5 in
      let test_finished = Atomic.make false in
 
      let a1 = Loc.make ~mode 0 in
@@ -220,7 +219,7 @@ let test_get_seq_xt () =
        done
      in
 
-     run_domains [ mutator; getter; getaser; committer; updater ]
+     Run.all [ mutator; getter; getaser; committer; updater ]
 
 (* *)
 
@@ -274,6 +273,7 @@ let test_presort_and_is_in_log_xt () =
   let n_incs = 10 * Util.iter_factor and n_domains = 3 and n_locs = 12 in
   let n_locs_half = n_locs asr 1 in
 
+  Scheduler.run ~n_domains @@ fun () ->
   let barrier = Barrier.make n_domains in
 
   let locs = Array.init n_locs (fun _ -> Loc.make 0) in
@@ -295,7 +295,7 @@ let test_presort_and_is_in_log_xt () =
     done
   in
 
-  run_domains (List.init n_domains (Fun.const thread));
+  Run.all (List.init n_domains (Fun.const thread));
 
   let sum = locs |> Array.map Loc.get |> Array.fold_left ( + ) 0 in
   assert (sum = n_incs * n_locs_half * n_domains)
@@ -344,6 +344,7 @@ let test_post_commit () =
 (* *)
 
 let test_blocking () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
   let state = Loc.make `Spawned in
   let await state' =
     (* Intentionally test that [Xt.modify] allows retry. *)
@@ -361,101 +362,109 @@ let test_blocking () =
 
   let num_attempts = ref 0 in
 
-  let other_domain =
-    Domain.spawn @@ fun () ->
-    Loc.set state `Get_a_non_zero;
-    Loc.get_as
-      (fun a ->
-        incr num_attempts;
-        Retry.unless (a != 0))
-      a;
-
-    Loc.set state `Update_a_zero;
-    Loc.modify a (fun a ->
-        incr num_attempts;
-        Retry.unless (a = 0);
-        a + 1);
-
-    Loc.set state `Set_1_b_to_0;
-    let bs = Array.copy bs in
-    for _ = 1 to n do
-      (* We access in random order to exercise tx log waiters handling. *)
-      in_place_shuffle bs;
-      let tx ~xt =
-        incr num_attempts;
-        match
-          bs
-          |> Array.find_map @@ fun b ->
-             if Xt.get ~xt b = 1 then Some b
-             else if Loc.has_awaiters b (* There must be no leaked waiters... *)
-             then begin
-               (* ...except if main domain just set the loc *)
-               assert (Loc.get b = 1);
-               Retry.later ()
-             end
-             else None
-        with
-        | None -> Retry.later ()
-        | Some b -> Xt.set ~xt b 0
-      in
-      Xt.commit { tx }
-    done
-  in
+  begin
+    Flock.join_after @@ fun () ->
+    begin
+      Flock.fork @@ fun () ->
+      Loc.set state `Get_a_non_zero;
+      Loc.get_as
+        (fun a ->
+          incr num_attempts;
+          Retry.unless (a != 0))
+        a;
+
+      Loc.set state `Update_a_zero;
+      Loc.modify a (fun a ->
+          incr num_attempts;
+          Retry.unless (a = 0);
+          a + 1);
+
+      Loc.set state `Set_1_b_to_0;
+      let bs = Array.copy bs in
+      for _ = 1 to n do
+        (* We access in random order to exercise tx log waiters handling. *)
+        in_place_shuffle bs;
+        let tx ~xt =
+          incr num_attempts;
+          match
+            bs
+            |> Array.find_map @@ fun b ->
+               if Xt.get ~xt b = 1 then Some b
+               else if
+                 Loc.has_awaiters b (* There must be no leaked waiters... *)
+               then begin
+                 (* ...except if main domain just set the loc *)
+                 assert (Loc.get b = 1);
+                 Retry.later ()
+               end
+               else None
+          with
+          | None -> Retry.later ()
+          | Some b -> Xt.set ~xt b 0
+        in
+        Xt.commit { tx }
+      done
+    end;
 
-  await `Get_a_non_zero;
-  Loc.set a 1;
-  assert (!num_attempts <= 2 + 1 (* Need to account for race to next. *));
+    await `Get_a_non_zero;
+    Loc.set a 1;
+    assert (!num_attempts <= 3 + 1 (* Need to account for race to next. *));
 
-  await `Update_a_zero;
-  Loc.set a 0;
-  assert (!num_attempts <= 4 + 1 (* Need to account for race to next. *));
+    await `Update_a_zero;
+    Loc.set a 0;
+    assert (!num_attempts <= 5 + 1 (* Need to account for race to next. *));
 
-  await `Set_1_b_to_0;
-  for _ = 1 to n do
-    let i = Random.int (Array.length bs) in
-    Loc.set bs.(i) 1;
-    Loc.get_as (fun b -> Retry.unless (b = 0)) bs.(i)
-  done;
-
-  Domain.join other_domain;
+    await `Set_1_b_to_0;
+    for _ = 1 to n do
+      let i = Random.int (Array.length bs) in
+      Loc.set bs.(i) 1;
+      Loc.get_as (fun b -> Retry.unless (b = 0)) bs.(i)
+    done
+  end;
 
-  assert (!num_attempts <= 4 + (n * 2));
+  assert (!num_attempts <= 5 + (n * 2));
   for i = 0 to Array.length bs - 1 do
     assert (not (Loc.has_awaiters bs.(i)))
   done
 
 let test_no_unnecessary_wakeups () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
   let continue = Loc.make false and tries = Atomic.make 0 in
 
-  let other_domain =
-    Domain.spawn @@ fun () ->
-    continue
-    |> Loc.get_as @@ fun s ->
-       Atomic.incr tries;
-       Retry.unless s
-  in
+  begin
+    Flock.join_after @@ fun () ->
+    begin
+      Flock.fork @@ fun () ->
+      continue
+      |> Loc.get_as @@ fun s ->
+         Atomic.incr tries;
+         Retry.unless s
+    end;
 
-  while not (Loc.has_awaiters continue) do
-    Domain.cpu_relax ()
-  done;
+    while not (Loc.has_awaiters continue) do
+      Domain.cpu_relax ()
+    done;
 
-  assert (Loc.compare_and_set continue false false);
-  assert (not (Loc.update continue Fun.id));
-  Loc.set continue false;
+    assert (Loc.compare_and_set continue false false);
+    assert (not (Loc.update continue Fun.id));
+    Loc.set continue false;
 
-  Unix.sleepf 0.01;
+    Unix.sleepf 0.01;
+
+    assert (Loc.has_awaiters continue && Atomic.get tries = 1);
+    Loc.set continue true
+  end;
 
-  assert (Loc.has_awaiters continue && Atomic.get tries = 1);
-  Loc.set continue true;
-  Domain.join other_domain;
   assert ((not (Loc.has_awaiters continue)) && Atomic.get tries = 2)
 
 (* *)
 
 let test_periodic_validation () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
+  Flock.join_after @@ fun () ->
   let a = Loc.make 0 and b = Loc.make 0 and looping = ref false in
   let non_zero_difference_domain =
-    Domain.spawn @@ fun () ->
+    Flock.fork_as_promise @@ fun () ->
     let rec tx ~xt =
       let d = Xt.get ~xt a - Xt.get ~xt b in
       if d <> 0 then d
@@ -475,7 +484,7 @@ let test_periodic_validation () =
 
   Loc.set a 1;
 
-  assert (1 = Domain.join non_zero_difference_domain)
+  assert (1 = Promise.await non_zero_difference_domain)
 
 (* *)
 
@@ -572,42 +581,43 @@ let test_call () =
 
 (** This is a non-deterministic test that might fail occasionally. *)
 let test_timeout () =
-  Domain_local_timeout.set_system (module Thread) (module Unix);
-
-  let check (op : ?timeoutf:float -> bool Loc.t -> unit) () =
+  Scheduler.run ~n_domains:5 @@ fun () ->
+  let check (op : bool Loc.t -> unit) () =
+    Flock.join_after @@ fun () ->
     let rec loop n =
       let x = Loc.make false in
-      let (_ : unit -> unit) =
-        Domain_local_timeout.set_timeoutf 0.6 @@ fun () -> Loc.set x true
+      let@ _ =
+        finally Promise.terminate @@ fun () ->
+        Flock.fork_as_promise @@ fun () ->
+        Control.sleep ~seconds:0.6;
+        Loc.set x true
       in
-      match op ~timeoutf:0.02 x with
+      match Control.terminate_after ~seconds:0.02 (fun () -> op x) with
       | () -> if 0 < n then loop (n - 1) else assert false
-      | exception Timeout.Timeout -> op ~timeoutf:2.0 x
+      | exception Control.Terminate ->
+          Control.terminate_after ~seconds:2.0 (fun () -> op x)
     in
     loop 10
   in
-  run_domains
+  Run.all
     [
-      check (fun ?timeoutf x ->
-          Loc.get_as ?timeoutf (fun x -> if not x then Retry.later ()) x);
-      check (fun ?timeoutf x ->
-          Loc.update ?timeoutf x (fun x -> x || Retry.later ()) |> ignore);
-      check (fun ?timeoutf x ->
-          Loc.modify ?timeoutf x (fun x -> x || Retry.later ()));
-      check (fun ?timeoutf x ->
+      check (fun x -> Loc.get_as (fun x -> if not x then Retry.later ()) x);
+      check (fun x -> Loc.update x (fun x -> x || Retry.later ()) |> ignore);
+      check (fun x -> Loc.modify x (fun x -> x || Retry.later ()));
+      check (fun x ->
           let y = Loc.make false in
           let tx ~xt =
             if not (Xt.get ~xt x) then Retry.later ();
             Xt.swap ~xt x y
           in
-          Xt.commit ?timeoutf { tx });
-      check (fun ?timeoutf x ->
+          Xt.commit { tx });
+      check (fun x ->
           let y = Loc.make false in
           let tx ~xt =
             if not (Xt.get ~xt x) then Retry.invalid ();
             Xt.swap ~xt x y
           in
-          Xt.commit ?timeoutf { tx });
+          Xt.commit { tx });
     ]
 
 (* *)
diff --git a/test/kcas/threads.ml b/test/kcas/threads.ml
index 5cbcc60c..5873a7ad 100644
--- a/test/kcas/threads.ml
+++ b/test/kcas/threads.ml
@@ -1,12 +1,14 @@
 open Kcas
 
 let await_between_threads () =
+  Scheduler.run @@ fun () ->
   let x = Loc.make 0 in
   let y = Loc.make 0 in
 
   let a_thread =
     ()
     |> Thread.create @@ fun () ->
+       Scheduler.run @@ fun () ->
        Loc.get_as (fun x -> Retry.unless (x <> 0)) x;
        Loc.set y 22
   in
diff --git a/test/kcas_data/accumulator_test_stm.ml b/test/kcas_data/accumulator_test_stm.ml
index 0565a9b0..1ac97a71 100644
--- a/test/kcas_data/accumulator_test_stm.ml
+++ b/test/kcas_data/accumulator_test_stm.ml
@@ -48,6 +48,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Accumulator" (module Spec)
-  |> exit
+let () = Stm_run.run ~name:"Accumulator" (module Spec) |> exit
diff --git a/test/kcas_data/dllist_test_stm.ml b/test/kcas_data/dllist_test_stm.ml
index c0dd7a84..669ce820 100644
--- a/test/kcas_data/dllist_test_stm.ml
+++ b/test/kcas_data/dllist_test_stm.ml
@@ -83,5 +83,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Dllist" (module Spec) |> exit
+let () = Stm_run.run ~name:"Dllist" (module Spec) |> exit
diff --git a/test/kcas_data/dune b/test/kcas_data/dune
index 1047e5a0..61167ee2 100644
--- a/test/kcas_data/dune
+++ b/test/kcas_data/dune
@@ -14,6 +14,8 @@
   stack_test_stm
   xt_test)
  (libraries
+  scheduler
+  picos.structured
   alcotest
   kcas
   kcas_data
diff --git a/test/kcas_data/hashtbl_test_stm.ml b/test/kcas_data/hashtbl_test_stm.ml
index f2cf2910..ff5a15a7 100644
--- a/test/kcas_data/hashtbl_test_stm.ml
+++ b/test/kcas_data/hashtbl_test_stm.ml
@@ -62,5 +62,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Hashtbl" (module Spec) |> exit
+let () = Stm_run.run ~name:"Hashtbl" (module Spec) |> exit
diff --git a/test/kcas_data/linearizable_chaining_example.ml b/test/kcas_data/linearizable_chaining_example.ml
index 58614b86..b3063af6 100644
--- a/test/kcas_data/linearizable_chaining_example.ml
+++ b/test/kcas_data/linearizable_chaining_example.ml
@@ -216,6 +216,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Hashtbl_with_order" (module Spec)
-  |> exit
+let () = Stm_run.run ~name:"Hashtbl_with_order" (module Spec) |> exit
diff --git a/test/kcas_data/lru_cache.ml b/test/kcas_data/lru_cache.ml
index 110ca832..c5271c07 100644
--- a/test/kcas_data/lru_cache.ml
+++ b/test/kcas_data/lru_cache.ml
@@ -62,8 +62,5 @@ end
 let capacity_of c = Kcas.Xt.commit { tx = Xt.capacity_of c }
 let set_capacity c n = Kcas.Xt.commit { tx = Xt.set_capacity c n }
 let get_opt c k = Kcas.Xt.commit { tx = Xt.get_opt c k }
-
-let set_blocking ?timeoutf c k v =
-  Kcas.Xt.commit ?timeoutf { tx = Xt.set_blocking c k v }
-
+let set_blocking c k v = Kcas.Xt.commit { tx = Xt.set_blocking c k v }
 let remove c k = Kcas.Xt.commit { tx = Xt.remove c k }
diff --git a/test/kcas_data/lru_cache.mli b/test/kcas_data/lru_cache.mli
index b32b1aa3..2162d524 100644
--- a/test/kcas_data/lru_cache.mli
+++ b/test/kcas_data/lru_cache.mli
@@ -9,10 +9,8 @@ module Xt :
   Lru_cache_intf.Ops
     with type ('k, 'v) t := ('k, 'v) t
     with type ('x, 'fn) fn := xt:'x Xt.t -> 'fn
-    with type ('x, 'fn) blocking_fn := xt:'x Xt.t -> 'fn
 
 include
   Lru_cache_intf.Ops
     with type ('k, 'v) t := ('k, 'v) t
     with type ('x, 'fn) fn := 'fn
-    with type ('x, 'fn) blocking_fn := ?timeoutf:float -> 'fn
diff --git a/test/kcas_data/lru_cache_example.ml b/test/kcas_data/lru_cache_example.ml
index 0df2ee29..709bf74f 100644
--- a/test/kcas_data/lru_cache_example.ml
+++ b/test/kcas_data/lru_cache_example.ml
@@ -1,3 +1,4 @@
+open Picos_structured
 open Kcas
 
 module Lru_cache = struct
@@ -19,21 +20,23 @@ module Lru_cache = struct
       | exception Retry.Later -> false
   end
 
-  let get ?timeoutf c k = Kcas.Xt.commit ?timeoutf { tx = Xt.get c k }
-  let get_if ?timeoutf c k p = Kcas.Xt.commit ?timeoutf { tx = Xt.get_if c k p }
+  let get c k = Kcas.Xt.commit { tx = Xt.get c k }
+  let get_if c k p = Kcas.Xt.commit { tx = Xt.get_if c k p }
   let try_set c k d = Kcas.Xt.commit { tx = Xt.try_set c k d }
 end
 
 let () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
+  Flock.join_after @@ fun () ->
   let c = Lru_cache.create 10 in
-  let domain =
-    Domain.spawn @@ fun () ->
+  let answer =
+    Flock.fork_as_promise @@ fun () ->
     let tx ~xt = Lru_cache.Xt.get ~xt c "a" + Lru_cache.Xt.get ~xt c "b" in
     Xt.commit { tx }
   in
   Lru_cache.set_blocking c "b" 30;
   Lru_cache.set_blocking c "a" 12;
-  assert (Domain.join domain = 42);
+  assert (Promise.await answer = 42);
   ()
 
 let () =
diff --git a/test/kcas_data/lru_cache_intf.ml b/test/kcas_data/lru_cache_intf.ml
index 79a8063e..11ef488d 100644
--- a/test/kcas_data/lru_cache_intf.ml
+++ b/test/kcas_data/lru_cache_intf.ml
@@ -1,11 +1,10 @@
 module type Ops = sig
   type ('k, 'v) t
   type ('x, 'fn) fn
-  type ('x, 'fn) blocking_fn
 
   val capacity_of : ('x, ('k, 'v) t -> int) fn
   val set_capacity : ('x, ('k, 'v) t -> int -> unit) fn
   val get_opt : ('x, ('k, 'v) t -> 'k -> 'v option) fn
-  val set_blocking : ('x, ('k, 'v) t -> 'k -> 'v -> unit) blocking_fn
+  val set_blocking : ('x, ('k, 'v) t -> 'k -> 'v -> unit) fn
   val remove : ('x, ('k, 'v) t -> 'k -> unit) fn
 end
diff --git a/test/kcas_data/mvar_test.ml b/test/kcas_data/mvar_test.ml
index f05872a4..07aecbf9 100644
--- a/test/kcas_data/mvar_test.ml
+++ b/test/kcas_data/mvar_test.ml
@@ -1,7 +1,10 @@
+open Picos_structured
 open Kcas
 open Kcas_data
 
 let basics () =
+  Scheduler.run ~n_domains:2 @@ fun () ->
+  Flock.join_after @@ fun () ->
   let mv = Mvar.create (Some 101) in
   assert (not (Mvar.is_empty mv));
   assert (Mvar.take mv = 101);
@@ -9,14 +12,13 @@ let basics () =
   assert (Mvar.take_opt mv = None);
   Mvar.put mv 42;
   let running = Mvar.create None in
-  let d =
-    Domain.spawn @@ fun () ->
+  begin
+    Flock.fork @@ fun () ->
     Mvar.put running ();
     Xt.commit { tx = Mvar.Xt.put mv 76 }
-  in
+  end;
   assert (Mvar.take running = ());
   assert (Xt.commit { tx = Mvar.Xt.take mv } = 42);
-  Domain.join d;
   assert (Mvar.take mv = 76)
 
 let () =
diff --git a/test/kcas_data/queue_test_stm.ml b/test/kcas_data/queue_test_stm.ml
index d3b0174e..63a166c6 100644
--- a/test/kcas_data/queue_test_stm.ml
+++ b/test/kcas_data/queue_test_stm.ml
@@ -64,5 +64,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Queue" (module Spec) |> exit
+let () = Stm_run.run ~name:"Queue" (module Spec) |> exit
diff --git a/test/kcas_data/stack_test_stm.ml b/test/kcas_data/stack_test_stm.ml
index 6dd8641a..0e3d62eb 100644
--- a/test/kcas_data/stack_test_stm.ml
+++ b/test/kcas_data/stack_test_stm.ml
@@ -54,5 +54,4 @@ module Spec = struct
     | _, _ -> false
 end
 
-let () =
-  Stm_run.run ~count:1000 ~verbose:true ~name:"Stack" (module Spec) |> exit
+let () = Stm_run.run ~name:"Stack" (module Spec) |> exit
diff --git a/test/lib/scheduler/dune b/test/lib/scheduler/dune
new file mode 100644
index 00000000..29be77cf
--- /dev/null
+++ b/test/lib/scheduler/dune
@@ -0,0 +1,9 @@
+(library
+ (name scheduler)
+ (libraries
+  picos.select
+  (select
+   scheduler.ml
+   from
+   (picos.randos -> scheduler.ocaml5.ml)
+   (picos.threaded -> scheduler.ocaml4.ml))))
diff --git a/test/lib/scheduler/scheduler.ocaml4.ml b/test/lib/scheduler/scheduler.ocaml4.ml
new file mode 100644
index 00000000..9ddf31b6
--- /dev/null
+++ b/test/lib/scheduler/scheduler.ocaml4.ml
@@ -0,0 +1 @@
+let run ?n_domains:_ main = Picos_threaded.run main
diff --git a/test/lib/scheduler/scheduler.ocaml5.ml b/test/lib/scheduler/scheduler.ocaml5.ml
new file mode 100644
index 00000000..ea7bb262
--- /dev/null
+++ b/test/lib/scheduler/scheduler.ocaml5.ml
@@ -0,0 +1,2 @@
+let () = Picos_select.configure ()
+let run ?(n_domains = 1) main = Picos_randos.run_on ~n_domains main
diff --git a/test/kcas_data/stm_run/dune b/test/lib/stm_run/dune
similarity index 100%
rename from test/kcas_data/stm_run/dune
rename to test/lib/stm_run/dune
diff --git a/test/kcas_data/stm_run/empty.ocaml4.ml b/test/lib/stm_run/empty.ocaml4.ml
similarity index 100%
rename from test/kcas_data/stm_run/empty.ocaml4.ml
rename to test/lib/stm_run/empty.ocaml4.ml
diff --git a/test/kcas_data/stm_run/empty.ocaml5.ml b/test/lib/stm_run/empty.ocaml5.ml
similarity index 100%
rename from test/kcas_data/stm_run/empty.ocaml5.ml
rename to test/lib/stm_run/empty.ocaml5.ml
diff --git a/test/kcas_data/stm_run/intf.ml b/test/lib/stm_run/intf.ml
similarity index 100%
rename from test/kcas_data/stm_run/intf.ml
rename to test/lib/stm_run/intf.ml
diff --git a/test/kcas_data/stm_run/stm_run.ocaml4.ml b/test/lib/stm_run/stm_run.ocaml4.ml
similarity index 69%
rename from test/kcas_data/stm_run/stm_run.ocaml4.ml
rename to test/lib/stm_run/stm_run.ocaml4.ml
index 7b8d851b..1986a993 100644
--- a/test/kcas_data/stm_run/stm_run.ocaml4.ml
+++ b/test/lib/stm_run/stm_run.ocaml4.ml
@@ -1,10 +1,6 @@
 include Intf
 
-let count =
-  let factor b = if b then 10 else 1 in
-  factor (64 <= Sys.word_size) * factor (Sys.backend_type = Native) * 10
-
-let run ?(verbose = true) ?(count = count) ?(budgetf = 60.0) ~name ?make_domain
+let run ?(verbose = true) ?(count = 1000) ?(budgetf = 60.0) ~name ?make_domain
     (module Spec : STM.Spec) =
   let module Seq = STM_sequential.Make (Spec) in
   let module Con = STM_thread.Make (Spec) [@alert "-experimental"] in
diff --git a/test/kcas_data/stm_run/stm_run.ocaml5.ml b/test/lib/stm_run/stm_run.ocaml5.ml
similarity index 73%
rename from test/kcas_data/stm_run/stm_run.ocaml5.ml
rename to test/lib/stm_run/stm_run.ocaml5.ml
index cece0a71..b69e72e4 100644
--- a/test/kcas_data/stm_run/stm_run.ocaml5.ml
+++ b/test/lib/stm_run/stm_run.ocaml5.ml
@@ -1,13 +1,7 @@
 include Intf
 
-let count =
-  let factor b = if b then 10 else 1 in
-  factor (64 <= Sys.word_size)
-  * factor (Sys.backend_type = Native)
-  * factor (1 < Domain.recommended_domain_count ())
-
-let run (type cmd state sut) ?(verbose = true) ?(count = count)
-    ?(budgetf = 60.0) ~name ?make_domain
+let run (type cmd state sut) ?(verbose = true) ?(count = 1000) ?(budgetf = 60.0)
+    ~name ?make_domain
     (module Spec : STM.Spec
       with type cmd = cmd
        and type state = state
diff --git a/test/kcas_data/stm_run/util.ml b/test/lib/stm_run/util.ml
similarity index 100%
rename from test/kcas_data/stm_run/util.ml
rename to test/lib/stm_run/util.ml