Source file `exninfo.ml`

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(************************************************************************)
(*         *   The Coq Proof Assistant / The Coq Development Team       *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
(************************************************************************)

(** 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 ()

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)

type backtrace = Printexc.raw_backtrace
let backtrace_to_string = Printexc.raw_backtrace_to_string

let backtrace_info : backtrace t = make "exninfo_backtrace"

let is_recording = ref false

let record_backtrace b =
  let () = Printexc.record_backtrace b in
  is_recording := b

let get_backtrace e = get e backtrace_info

let iraise (e,i) =
  CThread.with_lock lock ~scope:(fun () ->
      let id = Thread.id (Thread.self ()) in
      current := (id, (e,i)) :: remove_assoc id !current);
  match get i backtrace_info with
  | None ->
    raise e
  | Some bt ->
    Printexc.raise_with_backtrace e bt

let find_and_remove () =
  CThread.with_lock lock ~scope:(fun () ->
      let id = Thread.id (Thread.self ()) in
      let (v, l) = find_and_remove_assoc id !current in
      let () = current := l 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

let capture e =
  if !is_recording then
    (* This must be the first function call, otherwise the stack may be
       destroyed *)
    let bt = Printexc.get_raw_backtrace () in
    let info = info e in
    e, add info backtrace_info bt
  else
    e, info e

let reify () =
  if !is_recording then
    let bt = Printexc.get_callstack 50 in
    add null backtrace_info bt
  else
    null