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TLS: some documentation

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Simon Cruanes 2023-06-09 17:42:36 -04:00
parent 986057b99c
commit 04eafb04b1
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GPG key ID: EBFFF6F283F3A2B4
1 changed files with 11 additions and 4 deletions
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15
src/thread_local.ml
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@ -2,7 +2,7 @@ module A = Opentelemetry_atomic.Atomic
type key = int
let get_key_ () : key = Thread.id (Thread.self ())
let[@inline] get_key_ () : key = Thread.id (Thread.self ())
module Key_map_ = Map.Make (struct
type t = key
@ -11,10 +11,17 @@ module Key_map_ = Map.Make (struct
end)
type 'a t = 'a ref Key_map_.t A.t
(** The TLS variable is made of a global atomic reference
(which has very low contention: it's modified only when a
thread is started/stopped).
Inside that atomic variable, is a map from thread ID to a mutable [ref]
holding the actual data. Because this [ref] is only ever accessed
by the thread with this given ID, it's safe to modify. *)
let create () : _ t = A.make Key_map_.empty
let get_exn (self : _ t) =
let[@inline] get_exn (self : _ t) =
let m = A.get self in
let key = get_key_ () in
!(Key_map_.find key m)
@ -30,7 +37,7 @@ let[@inline] remove_ref_ self key : unit =
let m' = Key_map_.remove key m in
not (A.compare_and_set self m m')
do
()
Thread.yield ()
done
(* get or associate a reference to [key], and return it.
@ -48,7 +55,7 @@ let get_or_create_ref_ (self : _ t) key ~v : _ ref * _ option =
let m' = Key_map_.add key r m in
not (A.compare_and_set self m m')
do
()
Thread.yield ()
done;
r, None