diff --git a/src/core/exn_bt.ml b/src/core/exn_bt.ml
index e3d4c520..170db278 100644
--- a/src/core/exn_bt.ml
+++ b/src/core/exn_bt.ml
@@ -7,3 +7,7 @@ let show self = Printexc.to_string (exn self)
 let pp out self = Format.pp_print_string out (show self)
 
 type nonrec 'a result = ('a, t) result
+
+let[@inline] unwrap = function
+  | Ok x -> x
+  | Error ebt -> raise ebt
diff --git a/src/core/exn_bt.mli b/src/core/exn_bt.mli
index 37d075a8..55ff8177 100644
--- a/src/core/exn_bt.mli
+++ b/src/core/exn_bt.mli
@@ -21,3 +21,7 @@ val show : t -> string
 val pp : Format.formatter -> t -> unit
 
 type nonrec 'a result = ('a, t) result
+
+val unwrap : 'a result -> 'a
+(** [unwrap (Ok x)] is [x], [unwrap (Error ebt)] re-raises [ebt].
+    @since NEXT_RELEASE *)
diff --git a/src/core/fifo_pool.ml b/src/core/fifo_pool.ml
index 1fe4b708..ab2ed5c1 100644
--- a/src/core/fifo_pool.ml
+++ b/src/core/fifo_pool.ml
@@ -11,7 +11,7 @@ type state = {
   threads: Thread.t array;
   q: task_full Bb_queue.t;  (** Queue for tasks. *)
   around_task: WL.around_task;
-  as_runner: t lazy_t;
+  mutable as_runner: t;
   (* init options *)
   name: string option;
   on_init_thread: dom_id:int -> t_id:int -> unit -> unit;
@@ -24,7 +24,6 @@ type worker_state = {
   idx: int;
   dom_idx: int;
   st: state;
-  mutable current: fiber;
 }
 
 let[@inline] size_ (self : state) = Array.length self.threads
@@ -95,7 +94,7 @@ let cleanup (self : worker_state) : unit =
   self.st.on_exit_thread ~dom_id:self.dom_idx ~t_id ()
 
 let worker_ops : worker_state WL.ops =
-  let runner (st : worker_state) = Lazy.force st.st.as_runner in
+  let runner (st : worker_state) = st.st.as_runner in
   let around_task st = st.st.around_task in
   let on_exn (st : worker_state) (ebt : Exn_bt.t) =
     st.st.on_exn ebt.exn ebt.bt
@@ -111,9 +110,9 @@ let worker_ops : worker_state WL.ops =
     cleanup;
   }
 
-let create ?(on_init_thread = default_thread_init_exit_)
+let create_ ?(on_init_thread = default_thread_init_exit_)
     ?(on_exit_thread = default_thread_init_exit_) ?(on_exn = fun _ _ -> ())
-    ?around_task ?num_threads ?name () : t =
+    ?around_task ~threads ?name () : state =
   (* wrapper *)
   let around_task =
     match around_task with
@@ -121,6 +120,23 @@ let create ?(on_init_thread = default_thread_init_exit_)
     | None -> default_around_task_
   in
 
+  let self =
+    {
+      threads;
+      q = Bb_queue.create ();
+      around_task;
+      as_runner = Runner.dummy;
+      name;
+      on_init_thread;
+      on_exit_thread;
+      on_exn;
+    }
+  in
+  self.as_runner <- runner_of_state self;
+  self
+
+let create ?on_init_thread ?on_exit_thread ?on_exn ?around_task ?num_threads
+    ?name () : t =
   let num_domains = Domain_pool_.max_number_of_domains () in
 
   (* number of threads to run *)
@@ -129,20 +145,12 @@ let create ?(on_init_thread = default_thread_init_exit_)
   (* make sure we don't bias towards the first domain(s) in {!D_pool_} *)
   let offset = Random.int num_domains in
 
-  let rec pool =
+  let pool =
     let dummy_thread = Thread.self () in
-    {
-      threads = Array.make num_threads dummy_thread;
-      q = Bb_queue.create ();
-      around_task;
-      as_runner = lazy (runner_of_state pool);
-      name;
-      on_init_thread;
-      on_exit_thread;
-      on_exn;
-    }
+    let threads = Array.make num_threads dummy_thread in
+    create_ ?on_init_thread ?on_exit_thread ?on_exn ?around_task ~threads ?name
+      ()
   in
-
   let runner = runner_of_state pool in
 
   (* temporary queue used to obtain thread handles from domains
@@ -156,7 +164,7 @@ let create ?(on_init_thread = default_thread_init_exit_)
     (* function called in domain with index [i], to
        create the thread and push it into [receive_threads] *)
     let create_thread_in_domain () =
-      let st = { idx = i; dom_idx; st = pool; current = _dummy_fiber } in
+      let st = { idx = i; dom_idx; st = pool } in
       let thread = Thread.create (WL.worker_loop ~ops:worker_ops) st in
       (* send the thread from the domain back to us *)
       Bb_queue.push receive_threads (i, thread)
@@ -187,3 +195,14 @@ let with_ ?on_init_thread ?on_exit_thread ?on_exn ?around_task ?num_threads
   in
   let@ () = Fun.protect ~finally:(fun () -> shutdown pool) in
   f pool
+
+module Private_ = struct
+  type nonrec worker_state = worker_state
+
+  let worker_ops = worker_ops
+  let runner_of_state (self : worker_state) = worker_ops.runner self
+
+  let create_single_threaded_state ~thread ?on_exn () : worker_state =
+    let st : state = create_ ?on_exn ~threads:[| thread |] () in
+    { idx = 0; dom_idx = 0; st }
+end
diff --git a/src/core/fifo_pool.mli b/src/core/fifo_pool.mli
index 637586a9..11ba4ed5 100644
--- a/src/core/fifo_pool.mli
+++ b/src/core/fifo_pool.mli
@@ -44,3 +44,21 @@ val with_ : (unit -> (t -> 'a) -> 'a, _) create_args
     When [f pool] returns or fails, [pool] is shutdown and its resources
     are released.
     Most parameters are the same as in {!create}. *)
+
+(**/**)
+
+module Private_ : sig
+  type worker_state
+
+  val worker_ops : worker_state Worker_loop_.ops
+
+  val create_single_threaded_state :
+    thread:Thread.t ->
+    ?on_exn:(exn -> Printexc.raw_backtrace -> unit) ->
+    unit ->
+    worker_state
+
+  val runner_of_state : worker_state -> Runner.t
+end
+
+(**/**)
diff --git a/src/core/task_local_storage.ml b/src/core/task_local_storage.ml
index f9dd98e6..b66448af 100644
--- a/src/core/task_local_storage.ml
+++ b/src/core/task_local_storage.ml
@@ -1,83 +1,41 @@
 open Types_
-(*
-module A = Atomic_
+module PF = Picos.Fiber
 
-type 'a key = 'a ls_key
+type 'a t = 'a PF.FLS.t
 
-let key_count_ = A.make 0
+exception Not_set = PF.FLS.Not_set
 
-type t = local_storage
-type ls_value += Dummy
+let create = PF.FLS.create
 
-let dummy : t = _dummy_ls
+let[@inline] get_exn k =
+  let fiber = get_current_fiber_exn () in
+  PF.FLS.get_exn fiber k
 
-(** Resize array of TLS values *)
-let[@inline never] resize_ (cur : ls_value array ref) n =
-  if n > Sys.max_array_length then failwith "too many task local storage keys";
-  let len = Array.length !cur in
-  let new_ls =
-    Array.make (min Sys.max_array_length (max n ((len * 2) + 2))) Dummy
-  in
-  Array.blit !cur 0 new_ls 0 len;
-  cur := new_ls
-
-module Direct = struct
-  type nonrec t = t
-
-  let create = create_local_storage
-  let[@inline] copy (self : t) = ref (Array.copy !self)
-
-  let get (type a) (self : t) ((module K) : a key) : a =
-    if K.offset >= Array.length !self then resize_ self (K.offset + 1);
-    match !self.(K.offset) with
-    | K.V x -> (* common case first *) x
-    | Dummy ->
-      (* first time we access this *)
-      let v = K.init () in
-      !self.(K.offset) <- K.V v;
-      v
-    | _ -> assert false
-
-  let set (type a) (self : t) ((module K) : a key) (v : a) : unit =
-    assert (self != dummy);
-    if K.offset >= Array.length !self then resize_ self (K.offset + 1);
-    !self.(K.offset) <- K.V v;
-    ()
-end
-
-let new_key (type t) ~init () : t key =
-  let offset = A.fetch_and_add key_count_ 1 in
-  (module struct
-    type nonrec t = t
-    type ls_value += V of t
-
-    let offset = offset
-    let init = init
-  end : LS_KEY
-    with type t = t)
-
-let[@inline] get_cur_ () : ls_value array ref =
-  match get_current_storage () with
-  | Some r when r != dummy -> r
-  | _ -> failwith "Task local storage must be accessed from within a runner."
-
-let[@inline] get (key : 'a key) : 'a =
-  let cur = get_cur_ () in
-  Direct.get cur key
-
-let[@inline] get_opt key =
-  match get_current_storage () with
+let get_opt k =
+  match get_current_fiber () with
   | None -> None
-  | Some cur -> Some (Direct.get cur key)
+  | Some fiber ->
+    (match PF.FLS.get_exn fiber k with
+    | x -> Some x
+    | exception Not_set -> None)
 
-let[@inline] set key v : unit =
-  let cur = get_cur_ () in
-  Direct.set cur key v
+let[@inline] get k ~default =
+  let fiber = get_current_fiber_exn () in
+  PF.FLS.get fiber ~default k
 
-let with_value key x f =
-  let old = get key in
-  set key x;
-  Fun.protect ~finally:(fun () -> set key old) f
+let[@inline] set k v : unit =
+  let fiber = get_current_fiber_exn () in
+  PF.FLS.set fiber k v
 
-let get_current = get_current_storage
-*)
+let with_value k v (f : _ -> 'b) : 'b =
+  let fiber = get_current_fiber_exn () in
+
+  match PF.FLS.get_exn fiber k with
+  | exception Not_set ->
+    PF.FLS.set fiber k v;
+    (* nothing to restore back to, just call [f] *)
+    f ()
+  | old_v ->
+    PF.FLS.set fiber k v;
+    let finally () = PF.FLS.set fiber k old_v in
+    Fun.protect f ~finally
diff --git a/src/core/task_local_storage.mli b/src/core/task_local_storage.mli
index 4fad8e0e..69c07039 100644
--- a/src/core/task_local_storage.mli
+++ b/src/core/task_local_storage.mli
@@ -8,62 +8,31 @@
     @since 0.6
 *)
 
-(*
-type t = Types_.local_storage
-(** Underlying storage for a task. This is mutable and
-    not thread-safe. *)
+type 'a t = 'a Picos.Fiber.FLS.t
 
-val dummy : t
+val create : unit -> 'a t
+(** [create ()] makes a new key. Keys are expensive and
+    should never be allocated dynamically or in a loop. *)
 
-type 'a key
-(** A key used to access a particular (typed) storage slot on every task. *)
+exception Not_set
 
-val new_key : init:(unit -> 'a) -> unit -> 'a key
-(** [new_key ~init ()] makes a new key. Keys are expensive and
-    should never be allocated dynamically or in a loop.
-    The correct pattern is, at toplevel:
-
-    {[
-      let k_foo : foo Task_ocal_storage.key =
-        Task_local_storage.new_key ~init:(fun () -> make_foo ()) ()
-
-    (* … *)
-
-    (* use it: *)
-    let … = Task_local_storage.get k_foo
-    ]}
-*)
-
-val get : 'a key -> 'a
+val get_exn : 'a t -> 'a
 (** [get k] gets the value for the current task for key [k].
     Must be run from inside a task running on a runner.
-    @raise Failure otherwise *)
+    @raise Not_set otherwise *)
 
-val get_opt : 'a key -> 'a option
+val get_opt : 'a t -> 'a option
 (** [get_opt k] gets the current task's value for key [k],
     or [None] if not run from inside the task. *)
 
-val set : 'a key -> 'a -> unit
+val get : 'a t -> default:'a -> 'a
+
+val set : 'a t -> 'a -> unit
 (** [set k v] sets the storage for [k] to [v].
     Must be run from inside a task running on a runner.
     @raise Failure otherwise *)
 
-val with_value : 'a key -> 'a -> (unit -> 'b) -> 'b
+val with_value : 'a t -> 'a -> (unit -> 'b) -> 'b
 (** [with_value k v f] sets [k] to [v] for the duration of the call
     to [f()]. When [f()] returns (or fails), [k] is restored
     to its old value. *)
-
-val get_current : unit -> t option
-(** Access the current storage, or [None] if not run from
-    within a task. *)
-
-(** Direct access to values from a storage handle *)
-module Direct : sig
-  val get : t -> 'a key -> 'a
-  (** Access a key *)
-
-  val set : t -> 'a key -> 'a -> unit
-  val create : unit -> t
-  val copy : t -> t
-end
-*)
diff --git a/src/core/trigger.ml b/src/core/trigger.ml
index baad75ce..f7fda452 100644
--- a/src/core/trigger.ml
+++ b/src/core/trigger.ml
@@ -2,3 +2,5 @@
     @since NEXT_RELEASE *)
 
 include Picos.Trigger
+
+let[@inline] await_exn (self : t) = await self |> Option.iter Exn_bt.raise
diff --git a/src/core/ws_pool.ml b/src/core/ws_pool.ml
index ca31ef8a..70e4bb80 100644
--- a/src/core/ws_pool.ml
+++ b/src/core/ws_pool.ml
@@ -25,7 +25,7 @@ type state = {
   mutable n_waiting_nonzero: bool;  (** [n_waiting > 0] *)
   mutex: Mutex.t;
   cond: Condition.t;
-  as_runner: t lazy_t;
+  mutable as_runner: t;
   (* init options *)
   around_task: WL.around_task;
   name: string option;
@@ -167,7 +167,9 @@ and wait_on_worker (self : worker_state) : WL.task_full =
       | task ->
         Mutex.unlock self.st.mutex;
         task
-      | exception Queue.Empty -> try_steal_from_other_workers_ self
+      | exception Queue.Empty ->
+        Mutex.unlock self.st.mutex;
+        try_steal_from_other_workers_ self
     ) else (
       (* do nothing more: no task in main queue, and we are shutting
          down so no new task should arrive.
@@ -183,8 +185,7 @@ let before_start (self : worker_state) : unit =
   let t_id = Thread.id @@ Thread.self () in
   self.st.on_init_thread ~dom_id:self.dom_id ~t_id ();
   TLS.set k_cur_fiber _dummy_fiber;
-  TLS.set Runner.For_runner_implementors.k_cur_runner
-    (Lazy.force self.st.as_runner);
+  TLS.set Runner.For_runner_implementors.k_cur_runner self.st.as_runner;
   TLS.set k_worker_state self;
 
   (* set thread name *)
@@ -200,7 +201,7 @@ let cleanup (self : worker_state) : unit =
   self.st.on_exit_thread ~dom_id:self.dom_id ~t_id ()
 
 let worker_ops : worker_state WL.ops =
-  let runner (st : worker_state) = Lazy.force st.st.as_runner in
+  let runner (st : worker_state) = st.st.as_runner in
   let around_task st = st.st.around_task in
   let on_exn (st : worker_state) (ebt : Exn_bt.t) =
     st.st.on_exn ebt.exn ebt.bt
@@ -261,7 +262,7 @@ let create ?(on_init_thread = default_thread_init_exit_)
   (* make sure we don't bias towards the first domain(s) in {!D_pool_} *)
   let offset = Random.int num_domains in
 
-  let rec pool =
+  let pool =
     {
       id_ = pool_id_;
       active = A.make true;
@@ -276,28 +277,32 @@ let create ?(on_init_thread = default_thread_init_exit_)
       on_init_thread;
       on_exit_thread;
       name;
-      as_runner = lazy (as_runner_ pool);
+      as_runner = Runner.dummy;
     }
   in
+  pool.as_runner <- as_runner_ pool;
 
   (* temporary queue used to obtain thread handles from domains
      on which the thread are started. *)
   let receive_threads = Bb_queue.create () in
 
   (* start the thread with index [i] *)
-  let start_thread_with_idx idx =
+  let create_worker_state idx =
     let dom_id = (offset + idx) mod num_domains in
-    let st =
-      {
-        st = pool;
-        thread = (* dummy *) Thread.self ();
-        q = WSQ.create ~dummy:WL._dummy_task ();
-        rng = Random.State.make [| idx |];
-        dom_id;
-        idx;
-      }
-    in
+    {
+      st = pool;
+      thread = (* dummy *) Thread.self ();
+      q = WSQ.create ~dummy:WL._dummy_task ();
+      rng = Random.State.make [| idx |];
+      dom_id;
+      idx;
+    }
+  in
 
+  pool.workers <- Array.init num_threads create_worker_state;
+
+  (* start the thread with index [i] *)
+  let start_thread_with_idx idx (st : worker_state) =
     (* function called in domain with index [i], to
        create the thread and push it into [receive_threads] *)
     let create_thread_in_domain () =
@@ -305,15 +310,12 @@ let create ?(on_init_thread = default_thread_init_exit_)
       (* send the thread from the domain back to us *)
       Bb_queue.push receive_threads (idx, thread)
     in
-
-    Domain_pool_.run_on dom_id create_thread_in_domain;
-
-    st
+    Domain_pool_.run_on st.dom_id create_thread_in_domain
   in
 
   (* start all worker threads, placing them on the domains
      according to their index and [offset] in a round-robin fashion. *)
-  pool.workers <- Array.init num_threads start_thread_with_idx;
+  Array.iteri start_thread_with_idx pool.workers;
 
   (* receive the newly created threads back from domains *)
   for _j = 1 to num_threads do
@@ -322,7 +324,7 @@ let create ?(on_init_thread = default_thread_init_exit_)
     worker_state.thread <- th
   done;
 
-  Lazy.force pool.as_runner
+  pool.as_runner
 
 let with_ ?on_init_thread ?on_exit_thread ?on_exn ?around_task ?num_threads
     ?name () f =
diff --git a/src/fib/dune b/src/fib/dune
index 17ed239a..4c6594f8 100644
--- a/src/fib/dune
+++ b/src/fib/dune
@@ -2,7 +2,7 @@
  (name moonpool_fib)
  (public_name moonpool.fib)
  (synopsis "Fibers and structured concurrency for Moonpool")
- (libraries moonpool)
+ (libraries moonpool picos)
  (enabled_if
   (>= %{ocaml_version} 5.0))
  (flags :standard -open Moonpool_private -open Moonpool)
diff --git a/src/fib/fiber.ml b/src/fib/fiber.ml
index c50325b1..6fe034c0 100644
--- a/src/fib/fiber.ml
+++ b/src/fib/fiber.ml
@@ -1,6 +1,9 @@
+open Moonpool.Private.Types_
 module A = Atomic
 module FM = Handle.Map
 module Int_map = Map.Make (Int)
+module PF = Picos.Fiber
+module FLS = Picos.Fiber.FLS
 
 type 'a callback = 'a Exn_bt.result -> unit
 (** Callbacks that are called when a fiber is done. *)
@@ -10,13 +13,16 @@ type cancel_callback = Exn_bt.t -> unit
 let prom_of_fut : 'a Fut.t -> 'a Fut.promise =
   Fut.Private_.unsafe_promise_of_fut
 
+(* TODO: replace with picos structured at some point? *)
 module Private_ = struct
+  type pfiber = PF.t
+
   type 'a t = {
     id: Handle.t;  (** unique identifier for this fiber *)
     state: 'a state A.t;  (** Current state in the lifetime of the fiber *)
     res: 'a Fut.t;
     runner: Runner.t;
-    ls: Task_local_storage.t;
+    pfiber: pfiber;  (** Associated picos fiber *)
   }
 
   and 'a state =
@@ -30,11 +36,18 @@ module Private_ = struct
   and children = any FM.t
   and any = Any : _ t -> any [@@unboxed]
 
-  (** Key to access the current fiber. *)
-  let k_current_fiber : any option Task_local_storage.key =
-    Task_local_storage.new_key ~init:(fun () -> None) ()
+  (** Key to access the current moonpool.fiber. *)
+  let k_current_fiber : any FLS.t = FLS.create ()
 
-  let[@inline] get_cur () : any option = Task_local_storage.get k_current_fiber
+  exception Not_set = FLS.Not_set
+
+  let[@inline] get_cur_from_exn (pfiber : pfiber) : any =
+    FLS.get_exn pfiber k_current_fiber
+
+  let[@inline] get_cur_exn () : any =
+    get_cur_from_exn @@ get_current_fiber_exn ()
+
+  let[@inline] get_cur_opt () = try Some (get_cur_exn ()) with _ -> None
 
   let[@inline] is_closed (self : _ t) =
     match A.get self.state with
@@ -44,9 +57,9 @@ end
 
 include Private_
 
-let create_ ~ls ~runner () : 'a t =
+let create_ ~pfiber ~runner () : 'a t =
   let id = Handle.generate_fresh () in
-  let res, _promise = Fut.make () in
+  let res, _ = Fut.make () in
   {
     state =
       A.make
@@ -54,7 +67,7 @@ let create_ ~ls ~runner () : 'a t =
     id;
     res;
     runner;
-    ls;
+    pfiber;
   }
 
 let create_done_ ~res () : _ t =
@@ -66,7 +79,7 @@ let create_done_ ~res () : _ t =
     id;
     res;
     runner = Runner.dummy;
-    ls = Task_local_storage.dummy;
+    pfiber = Moonpool.Private.Types_._dummy_fiber;
   }
 
 let[@inline] return x = create_done_ ~res:(Fut.return x) ()
@@ -175,7 +188,8 @@ let with_on_cancel (self : _ t) cb (k : unit -> 'a) : 'a =
   let h = add_on_cancel self cb in
   Fun.protect k ~finally:(fun () -> remove_on_cancel self h)
 
-(** Successfully resolve the fiber *)
+(** Successfully resolve the fiber. This might still fail if
+    some children failed. *)
 let resolve_ok_ (self : 'a t) (r : 'a) : unit =
   let r = A.make @@ Ok r in
   let promise = prom_of_fut self.res in
@@ -239,15 +253,21 @@ let add_child_ ~protect (self : _ t) (child : _ t) =
     ()
   done
 
-let spawn_ ~ls ~parent ~runner (f : unit -> 'a) : 'a t =
+let spawn_ ~parent ~runner (f : unit -> 'a) : 'a t =
+  let comp = Picos.Computation.create () in
+  let pfiber = PF.create ~forbid:false comp in
+
+  (* inherit FLS from parent, if present *)
+  Option.iter (fun (p : _ t) -> PF.copy_fls p.pfiber pfiber) parent;
+
   (match parent with
   | Some p when is_closed p -> failwith "spawn: nursery is closed"
   | _ -> ());
-  let fib = create_ ~ls ~runner () in
+  let fib = create_ ~pfiber ~runner () in
 
   let run () =
     (* make sure the fiber is accessible from inside itself *)
-    Task_local_storage.set k_current_fiber (Some (Any fib));
+    FLS.set pfiber k_current_fiber (Any fib);
     try
       let res = f () in
       resolve_ok_ fib res
@@ -257,63 +277,54 @@ let spawn_ ~ls ~parent ~runner (f : unit -> 'a) : 'a t =
       resolve_as_failed_ fib ebt
   in
 
-  Runner.run_async ~ls runner run;
+  Runner.run_async ~fiber:pfiber runner run;
 
   fib
 
-let spawn_top ~on f : _ t =
-  let ls = Task_local_storage.Direct.create () in
-  spawn_ ~ls ~runner:on ~parent:None f
+let spawn_top ~on f : _ t = spawn_ ~runner:on ~parent:None f
 
 let spawn ?on ?(protect = true) f : _ t =
   (* spawn [f()] with a copy of our local storage *)
   let (Any p) =
-    match get_cur () with
-    | None -> failwith "Fiber.spawn: must be run from within another fiber."
-    | Some p -> p
+    try get_cur_exn ()
+    with Not_set ->
+      failwith "Fiber.spawn: must be run from within another fiber."
   in
-  let ls = Task_local_storage.Direct.copy p.ls in
+
   let runner =
     match on with
     | Some r -> r
     | None -> p.runner
   in
-  let child = spawn_ ~ls ~parent:(Some p) ~runner f in
+  let child = spawn_ ~parent:(Some p) ~runner f in
   add_child_ ~protect p child;
   child
 
 let[@inline] spawn_ignore ?protect f : unit = ignore (spawn ?protect f : _ t)
 
 let[@inline] self () : any =
-  match Task_local_storage.get k_current_fiber with
-  | None -> failwith "Fiber.self: must be run from inside a fiber."
-  | Some f -> f
+  match get_cur_exn () with
+  | exception Not_set -> failwith "Fiber.self: must be run from inside a fiber."
+  | f -> f
 
 let with_on_self_cancel cb (k : unit -> 'a) : 'a =
   let (Any self) = self () in
   let h = add_on_cancel self cb in
   Fun.protect k ~finally:(fun () -> remove_on_cancel self h)
 
-module Suspend_ = Moonpool.Private.Suspend_
-
-let check_if_cancelled_ (self : _ t) =
-  match A.get self.state with
-  | Terminating_or_done r ->
-    (match A.get r with
-    | Error ebt -> Exn_bt.raise ebt
-    | _ -> ())
-  | _ -> ()
+let[@inline] check_if_cancelled_ (self : _ t) = PF.check self.pfiber
 
 let check_if_cancelled () =
-  match Task_local_storage.get k_current_fiber with
-  | None ->
+  match get_cur_exn () with
+  | exception Not_set ->
     failwith "Fiber.check_if_cancelled: must be run from inside a fiber."
-  | Some (Any self) -> check_if_cancelled_ self
+  | Any self -> check_if_cancelled_ self
 
 let yield () : unit =
-  match Task_local_storage.get k_current_fiber with
-  | None -> failwith "Fiber.yield: must be run from inside a fiber."
-  | Some (Any self) ->
+  match get_cur_exn () with
+  | exception Not_set ->
+    failwith "Fiber.yield: must be run from inside a fiber."
+  | Any self ->
     check_if_cancelled_ self;
-    Suspend_.yield ();
+    PF.yield ();
     check_if_cancelled_ self
diff --git a/src/fib/fiber.mli b/src/fib/fiber.mli
index d02c4e56..0da300e7 100644
--- a/src/fib/fiber.mli
+++ b/src/fib/fiber.mli
@@ -17,20 +17,27 @@ type cancel_callback = Exn_bt.t -> unit
 (** Do not rely on this, it is internal implementation details. *)
 module Private_ : sig
   type 'a state
+  type pfiber
 
   type 'a t = private {
     id: Handle.t;  (** unique identifier for this fiber *)
     state: 'a state Atomic.t;  (** Current state in the lifetime of the fiber *)
     res: 'a Fut.t;
     runner: Runner.t;
-    ls: Task_local_storage.t;
+    pfiber: pfiber;
   }
   (** Type definition, exposed so that {!any} can be unboxed.
       Please do not rely on that. *)
 
   type any = Any : _ t -> any [@@unboxed]
 
-  val get_cur : unit -> any option
+  exception Not_set
+
+  val get_cur_exn : unit -> any
+  (** [get_cur_exn ()] either returns the current fiber, or
+      @raise Not_set if run outside a fiber. *)
+
+  val get_cur_opt : unit -> any option
 end
 
 (**/**)
diff --git a/src/fib/main.ml b/src/fib/main.ml
index 26112015..0ec22be8 100644
--- a/src/fib/main.ml
+++ b/src/fib/main.ml
@@ -1,14 +1,20 @@
 exception Oh_no of Exn_bt.t
 
 let main (f : Runner.t -> 'a) : 'a =
-  let st = Fifo_pool.Private_.create_state ~threads:[| Thread.self () |] () in
-  let runner = Fifo_pool.Private_.runner_of_state st in
+  let worker_st =
+    Fifo_pool.Private_.create_single_threaded_state ~thread:(Thread.self ())
+      ~on_exn:(fun e bt -> raise (Oh_no (Exn_bt.make e bt)))
+      ()
+  in
+  let runner = Fifo_pool.Private_.runner_of_state worker_st in
   try
     let fiber = Fiber.spawn_top ~on:runner (fun () -> f runner) in
     Fiber.on_result fiber (fun _ -> Runner.shutdown_without_waiting runner);
+
     (* run the main thread *)
-    Fifo_pool.Private_.run_thread st runner ~on_exn:(fun e bt ->
-        raise (Oh_no (Exn_bt.make e bt)));
+    Moonpool.Private.Worker_loop_.worker_loop worker_st
+      ~ops:Fifo_pool.Private_.worker_ops;
+
     match Fiber.peek fiber with
     | Some (Ok x) -> x
     | Some (Error ebt) -> Exn_bt.raise ebt
diff --git a/src/forkjoin/dune b/src/forkjoin/dune
index b17a163d..84849c9b 100644
--- a/src/forkjoin/dune
+++ b/src/forkjoin/dune
@@ -6,4 +6,4 @@
  (optional)
  (enabled_if
   (>= %{ocaml_version} 5.0))
- (libraries moonpool moonpool.private))
+ (libraries moonpool moonpool.private picos))
diff --git a/src/forkjoin/moonpool_forkjoin.ml b/src/forkjoin/moonpool_forkjoin.ml
index d5961d95..80cead1d 100644
--- a/src/forkjoin/moonpool_forkjoin.ml
+++ b/src/forkjoin/moonpool_forkjoin.ml
@@ -1,5 +1,4 @@
 module A = Moonpool.Atomic
-module Suspend_ = Moonpool.Private.Suspend_
 module Domain_ = Moonpool_private.Domain_
 
 module State_ = struct
@@ -9,7 +8,7 @@ module State_ = struct
   type ('a, 'b) t =
     | Init
     | Left_solved of 'a or_error
-    | Right_solved of 'b or_error * Suspend_.suspension
+    | Right_solved of 'b or_error * Trigger.t
     | Both_solved of 'a or_error * 'b or_error
 
   let get_exn_ (self : _ t A.t) =
@@ -28,13 +27,13 @@ module State_ = struct
         Domain_.relax ();
         set_left_ self left
       )
-    | Right_solved (right, cont) ->
+    | Right_solved (right, tr) ->
       let new_st = Both_solved (left, right) in
       if not (A.compare_and_set self old_st new_st) then (
         Domain_.relax ();
         set_left_ self left
       ) else
-        cont (Ok ())
+        Trigger.signal tr
     | Left_solved _ | Both_solved _ -> assert false
 
   let rec set_right_ (self : _ t A.t) (right : _ or_error) : unit =
@@ -45,27 +44,27 @@ module State_ = struct
       if not (A.compare_and_set self old_st new_st) then set_right_ self right
     | Init ->
       (* we are first arrived, we suspend until the left computation is done *)
-      Suspend_.suspend
-        {
-          Suspend_.handle =
-            (fun ~run:_ ~resume suspension ->
-              while
-                let old_st = A.get self in
-                match old_st with
-                | Init ->
-                  not
-                    (A.compare_and_set self old_st
-                       (Right_solved (right, suspension)))
-                | Left_solved left ->
-                  (* other thread is done, no risk of race condition *)
-                  A.set self (Both_solved (left, right));
-                  resume suspension (Ok ());
-                  false
-                | Right_solved _ | Both_solved _ -> assert false
-              do
-                ()
-              done);
-        }
+      let trigger = Trigger.create () in
+      let must_await = ref true in
+
+      while
+        let old_st = A.get self in
+        match old_st with
+        | Init ->
+          (* setup trigger so that left computation will wake us up *)
+          not (A.compare_and_set self old_st (Right_solved (right, trigger)))
+        | Left_solved left ->
+          (* other thread is done, no risk of race condition *)
+          A.set self (Both_solved (left, right));
+          must_await := false;
+          false
+        | Right_solved _ | Both_solved _ -> assert false
+      do
+        ()
+      done;
+
+      (* wait for the other computation to be done *)
+      if !must_await then Trigger.await trigger |> Option.iter Exn_bt.raise
     | Right_solved _ | Both_solved _ -> assert false
 end
 
@@ -102,7 +101,12 @@ let both_ignore f g = ignore (both f g : _ * _)
 
 let for_ ?chunk_size n (f : int -> int -> unit) : unit =
   if n > 0 then (
-    let has_failed = A.make false in
+    let runner =
+      match Runner.get_current_runner () with
+      | None -> failwith "forkjoin.for_: must be run inside a moonpool runner."
+      | Some r -> r
+    in
+    let failure = A.make None in
     let missing = A.make n in
 
     let chunk_size =
@@ -113,40 +117,36 @@ let for_ ?chunk_size n (f : int -> int -> unit) : unit =
         max 1 (1 + (n / Moonpool.Private.num_domains ()))
     in
 
-    let start_tasks ~run ~resume (suspension : Suspend_.suspension) =
-      let task_for ~offset ~len_range =
-        match f offset (offset + len_range - 1) with
-        | () ->
-          if A.fetch_and_add missing (-len_range) = len_range then
-            (* all tasks done successfully *)
-            resume suspension (Ok ())
-        | exception exn ->
-          let bt = Printexc.get_raw_backtrace () in
-          if not (A.exchange has_failed true) then
-            (* first one to fail, and [missing] must be >= 2
-               because we're not decreasing it. *)
-            resume suspension (Error { Exn_bt.exn; bt })
-      in
+    let trigger = Trigger.create () in
 
-      let i = ref 0 in
-      while !i < n do
-        let offset = !i in
-
-        let len_range = min chunk_size (n - offset) in
-        assert (offset + len_range <= n);
-
-        run (fun () -> task_for ~offset ~len_range);
-        i := !i + len_range
-      done
+    let task_for ~offset ~len_range =
+      match f offset (offset + len_range - 1) with
+      | () ->
+        if A.fetch_and_add missing (-len_range) = len_range then
+          (* all tasks done successfully *)
+          Trigger.signal trigger
+      | exception exn ->
+        let bt = Printexc.get_raw_backtrace () in
+        if Option.is_none (A.exchange failure (Some { Exn_bt.exn; bt })) then
+          (* first one to fail, and [missing] must be >= 2
+             because we're not decreasing it. *)
+          Trigger.signal trigger
     in
 
-    Suspend_.suspend
-      {
-        Suspend_.handle =
-          (fun ~run ~resume suspension ->
-            (* run tasks, then we'll resume [suspension] *)
-            start_tasks ~run ~resume suspension);
-      }
+    let i = ref 0 in
+    while !i < n do
+      let offset = !i in
+
+      let len_range = min chunk_size (n - offset) in
+      assert (offset + len_range <= n);
+
+      Runner.run_async runner (fun () -> task_for ~offset ~len_range);
+      i := !i + len_range
+    done;
+
+    Trigger.await trigger |> Option.iter Exn_bt.raise;
+    Option.iter Exn_bt.raise @@ A.get failure;
+    ()
   )
 
 let all_array ?chunk_size (fs : _ array) : _ array =
diff --git a/src/lwt/IO.ml b/src/lwt/IO.ml
index 4a8acc69..6ae09506 100644
--- a/src/lwt/IO.ml
+++ b/src/lwt/IO.ml
@@ -1,17 +1,14 @@
 open Base
 
 let await_readable fd : unit =
-  Moonpool.Private.Suspend_.suspend
-    {
-      handle =
-        (fun ~run:_ ~resume sus ->
-          Perform_action_in_lwt.schedule
-          @@ Action.Wait_readable
-               ( fd,
-                 fun cancel ->
-                   resume sus @@ Ok ();
-                   Lwt_engine.stop_event cancel ));
-    }
+  let trigger = Trigger.create () in
+  Perform_action_in_lwt.schedule
+  @@ Action.Wait_readable
+       ( fd,
+         fun cancel ->
+           Trigger.signal trigger;
+           Lwt_engine.stop_event cancel );
+  Trigger.await_exn trigger
 
 let rec read fd buf i len : int =
   if len = 0 then
@@ -25,17 +22,14 @@ let rec read fd buf i len : int =
   )
 
 let await_writable fd =
-  Moonpool.Private.Suspend_.suspend
-    {
-      handle =
-        (fun ~run:_ ~resume sus ->
-          Perform_action_in_lwt.schedule
-          @@ Action.Wait_writable
-               ( fd,
-                 fun cancel ->
-                   resume sus @@ Ok ();
-                   Lwt_engine.stop_event cancel ));
-    }
+  let trigger = Trigger.create () in
+  Perform_action_in_lwt.schedule
+  @@ Action.Wait_writable
+       ( fd,
+         fun cancel ->
+           Trigger.signal trigger;
+           Lwt_engine.stop_event cancel );
+  Trigger.await_exn trigger
 
 let rec write_once fd buf i len : int =
   if len = 0 then
@@ -59,16 +53,14 @@ let write fd buf i len : unit =
 
 (** Sleep for the given amount of seconds *)
 let sleep_s (f : float) : unit =
-  if f > 0. then
-    Moonpool.Private.Suspend_.suspend
-      {
-        handle =
-          (fun ~run:_ ~resume sus ->
-            Perform_action_in_lwt.schedule
-            @@ Action.Sleep
-                 ( f,
-                   false,
-                   fun cancel ->
-                     resume sus @@ Ok ();
-                     Lwt_engine.stop_event cancel ));
-      }
+  if f > 0. then (
+    let trigger = Trigger.create () in
+    Perform_action_in_lwt.schedule
+    @@ Action.Sleep
+         ( f,
+           false,
+           fun cancel ->
+             Trigger.signal trigger;
+             Lwt_engine.stop_event cancel );
+    Trigger.await_exn trigger
+  )
diff --git a/src/lwt/base.ml b/src/lwt/base.ml
index 73ccc049..e61b71aa 100644
--- a/src/lwt/base.ml
+++ b/src/lwt/base.ml
@@ -1,4 +1,5 @@
 open Common_
+module Trigger = M.Trigger
 module Fiber = Moonpool_fib.Fiber
 module FLS = Moonpool_fib.Fls
 
@@ -14,7 +15,7 @@ module Action = struct
     | Sleep of float * bool * cb
     (* TODO: provide actions with cancellation, alongside a "select" operation *)
     (* | Cancel of event *)
-    | On_termination : 'a Lwt.t * ('a Exn_bt.result -> unit) -> t
+    | On_termination : 'a Lwt.t * 'a Exn_bt.result ref * Trigger.t -> t
     | Wakeup : 'a Lwt.u * 'a -> t
     | Wakeup_exn : _ Lwt.u * exn -> t
     | Other of (unit -> unit)
@@ -26,10 +27,14 @@ module Action = struct
     | Wait_writable (fd, cb) -> ignore (Lwt_engine.on_writable fd cb : event)
     | Sleep (f, repeat, cb) -> ignore (Lwt_engine.on_timer f repeat cb : event)
     (* | Cancel ev -> Lwt_engine.stop_event ev *)
-    | On_termination (fut, f) ->
+    | On_termination (fut, res, trigger) ->
       Lwt.on_any fut
-        (fun x -> f @@ Ok x)
-        (fun exn -> f @@ Error (Exn_bt.get_callstack 10 exn))
+        (fun x ->
+          res := Ok x;
+          Trigger.signal trigger)
+        (fun exn ->
+          res := Error (Exn_bt.get_callstack 10 exn);
+          Trigger.signal trigger)
     | Wakeup (prom, x) -> Lwt.wakeup prom x
     | Wakeup_exn (prom, e) -> Lwt.wakeup_exn prom e
     | Other f -> f ()
@@ -106,23 +111,19 @@ let fut_of_lwt (lwt_fut : _ Lwt.t) : _ M.Fut.t =
         M.Fut.fulfill prom (Error { Exn_bt.exn; bt }));
     fut
 
+let _dummy_exn_bt : Exn_bt.t =
+  Exn_bt.get_callstack 0 (Failure "dummy Exn_bt from moonpool-lwt")
+
 let await_lwt (fut : _ Lwt.t) =
   match Lwt.poll fut with
   | Some x -> x
   | None ->
     (* suspend fiber, wake it up when [fut] resolves *)
-    M.Private.Suspend_.suspend
-      {
-        handle =
-          (fun ~run:_ ~resume sus ->
-            let on_lwt_done _ = resume sus @@ Ok () in
-            Perform_action_in_lwt.(
-              schedule Action.(On_termination (fut, on_lwt_done))));
-      };
-
-    (match Lwt.poll fut with
-    | Some x -> x
-    | None -> assert false)
+    let trigger = M.Trigger.create () in
+    let res = ref (Error _dummy_exn_bt) in
+    Perform_action_in_lwt.(schedule Action.(On_termination (fut, res, trigger)));
+    Trigger.await trigger |> Option.iter Exn_bt.raise;
+    Exn_bt.unwrap !res
 
 let run_in_lwt f : _ M.Fut.t =
   let fut, prom = M.Fut.make () in
diff --git a/src/lwt/dune b/src/lwt/dune
index 9038747a..b03d03d6 100644
--- a/src/lwt/dune
+++ b/src/lwt/dune
@@ -4,4 +4,9 @@
  (private_modules common_)
  (enabled_if
   (>= %{ocaml_version} 5.0))
- (libraries moonpool moonpool.fib lwt lwt.unix))
+ (libraries
+  (re_export moonpool)
+  (re_export moonpool.fib)
+  picos
+  (re_export lwt)
+  lwt.unix))