eio local storage

src/ambient-context/eio/dune

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+(library
+ (name opentelemetry_ambient_context_eio)
+ (public_name opentelemetry.ambient-context.eio)
+ (synopsis
+  "Storage backend for ambient-context using Eio's fibre-local storage")
+ (optional) ; eio
+ (libraries eio hmap opentelemetry.ambient-context thread-local-storage))

src/ambient-context/eio/opentelemetry_ambient_context_eio.ml

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+module TLS = Thread_local_storage
+module Fiber = Eio.Fiber
+
+open struct
+  let _internal_key : Hmap.t Fiber.key = Fiber.create_key ()
+
+  let ( let* ) = Option.bind
+end
+
+module M = struct
+  let name = "Storage_eio"
+
+  let[@inline] get_map () = Fiber.get _internal_key
+
+  let[@inline] with_map m cb = Fiber.with_binding _internal_key m cb
+
+  let create_key = Hmap.Key.create
+
+  let get k =
+    let* context = get_map () in
+    Hmap.find k context
+
+  let with_binding k v cb =
+    let new_context =
+      match get_map () with
+      | None -> Hmap.singleton k v
+      | Some old_context -> Hmap.add k v old_context
+    in
+    with_map new_context cb
+
+  let without_binding k cb =
+    let new_context =
+      match get_map () with
+      | None -> Hmap.empty
+      | Some old_context -> Hmap.rem k old_context
+    in
+    with_map new_context cb
+end
+
+let storage () : Opentelemetry_ambient_context.storage = (module M)

src/ambient-context/eio/opentelemetry_ambient_context_eio.mli

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+val storage : unit -> Opentelemetry_ambient_context.storage
+(** Storage using Eio's fibers local storage *)