diff --git a/src/core/worker_loop_.mli b/src/core/worker_loop_.mli
new file mode 100644
index 00000000..e5b0c969
--- /dev/null
+++ b/src/core/worker_loop_.mli
@@ -0,0 +1,37 @@
+(** Internal module that is used for workers.
+
+    A thread pool should use this [worker_loop] to run tasks,
+    handle effects, etc. *)
+
+open Types_
+
+type task_full =
+  | T_start of {
+      fiber: fiber;
+      f: unit -> unit;
+    }
+  | T_resume : {
+      fiber: fiber;
+      k: unit -> unit;
+    }
+      -> task_full
+
+val _dummy_task : task_full
+
+type around_task =
+  | AT_pair : (Runner.t -> 'a) * (Runner.t -> 'a -> unit) -> around_task
+
+exception No_more_tasks
+
+type 'st ops = {
+  schedule: 'st -> task_full -> unit;
+  get_next_task: 'st -> task_full;
+  get_thread_state: unit -> 'st;
+  around_task: 'st -> around_task;
+  on_exn: 'st -> Exn_bt.t -> unit;
+  runner: 'st -> Runner.t;
+  before_start: 'st -> unit;
+  cleanup: 'st -> unit;
+}
+
+val worker_loop : block_signals:bool -> ops:'st ops -> 'st -> unit