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diff --git a/lib/exninfo.ml b/lib/exninfo.ml
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+(***********************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team    *)
+(* <O___,, *        INRIA-Rocquencourt  &  LRI-CNRS-Orsay              *)
+(*   \VV/  *************************************************************)
+(*    //   *      This file is distributed under the terms of the      *)
+(*         *       GNU Lesser General Public License Version 2.1       *)
+(***********************************************************************)
+
+(** Enriched exceptions have an additional field at the end of their usual data
+    containing a pair composed of the distinguishing [token] and the backtrace
+    information. We discriminate the token by pointer equality. *)
+
+module Store = Store.Make(struct end)
+
+type 'a t = 'a Store.field
+
+type info = Store.t
+
+type iexn = exn * info
+
+let make = Store.field
+let add = Store.set
+let get = Store.get
+let null = Store.empty
+
+exception Unique
+
+let dummy = (Unique, Store.empty)
+
+let current : (int * iexn) list ref = ref []
+(** List associating to each thread id the latest exception raised by an
+    instrumented raise (i.e. {!raise} from this module). It is shared between
+    threads, so we must take care of this when modifying it.
+
+    Invariants: all index keys are unique in the list.
+*)
+
+let lock = Mutex.create ()
+
+let rec remove_assoc (i : int) = function
+| [] -> []
+| (j, v) :: rem as l ->
+  if i = j then rem
+  else
+    let ans = remove_assoc i rem in
+    if rem == ans then l
+    else (j, v) :: ans
+
+let rec find_and_remove_assoc (i : int) = function
+| [] -> dummy, []
+| (j, v) :: rem as l ->
+  if i = j then (v, rem)
+  else
+    let (r, ans) = find_and_remove_assoc i rem in
+    if rem == ans then (r, l)
+    else (r, (j, v) :: ans)
+
+let iraise e =
+  let () = Mutex.lock lock in
+  let id = Thread.id (Thread.self ()) in
+  let () = current := (id, e) :: remove_assoc id !current in
+  let () = Mutex.unlock lock in
+  raise (fst e)
+
+let raise ?info e = match info with
+| None ->
+  let () = Mutex.lock lock in
+  let id = Thread.id (Thread.self ()) in
+  let () = current := remove_assoc id !current in
+  let () = Mutex.unlock lock in
+  raise e
+| Some i ->
+  let () = Mutex.lock lock in
+  let id = Thread.id (Thread.self ()) in
+  let () = current := (id, (e, i)) :: remove_assoc id !current in
+  let () = Mutex.unlock lock in
+  raise e
+
+let find_and_remove () =
+  let () = Mutex.lock lock in
+  let id = Thread.id (Thread.self ()) in
+  let (v, l) = find_and_remove_assoc id !current in
+  let () = current := l in
+  let () = Mutex.unlock lock in
+  v
+
+let info e =
+  let (src, data) = find_and_remove () in
+  if src == e then
+    (** Slightly unsound, some exceptions may not be unique up to pointer
+        equality. Though, it should be quite exceptional to be in a situation
+        where the following holds:
+
+        1. An argument-free exception is raised through the enriched {!raise};
+        2. It is not captured by any enriched with-clause (which would reset
+            the current data);
+        3. The same exception is raised through the standard raise, accessing
+            the wrong data.
+    . *)
+    data
+  else
+    (** Mismatch: the raised exception is not the one stored, either because the
+        previous raise was not instrumented, or because something went wrong. *)
+    Store.empty