From d5de65fdb1802cdf498d65d93397f290813c377c Mon Sep 17 00:00:00 2001 From: muqiuhan Date: Tue, 9 Sep 2025 06:17:00 +0000 Subject: deploy: 9665097f0fa0dae9f92123fac54d26c0818758a5 --- .../index.html" | 10 ++++------ .../index.html" | 3 +-- 2 files changed, 5 insertions(+), 8 deletions(-) (limited to '2023/06/28') diff --git "a/2023/06/28/caml-release-runtime-system\345\257\274\350\207\264\347\232\204\346\255\273\351\224\201\351\227\256\351\242\230/index.html" "b/2023/06/28/caml-release-runtime-system\345\257\274\350\207\264\347\232\204\346\255\273\351\224\201\351\227\256\351\242\230/index.html" index dfa25769..e0b982f0 100644 --- "a/2023/06/28/caml-release-runtime-system\345\257\274\350\207\264\347\232\204\346\255\273\351\224\201\351\227\256\351\242\230/index.html" +++ "b/2023/06/28/caml-release-runtime-system\345\257\274\350\207\264\347\232\204\346\255\273\351\224\201\351\227\256\351\242\230/index.html" @@ -194,19 +194,17 @@

给出一个test.ml:

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Printf.eprintf "hello from OCaml\n%!"
-

和test-ocaml-5.c:

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#include <stdio.h>
#include <stdlib.h>
#include <caml/misc.h>
#include <caml/callback.h>
#include <caml/threads.h>

int
main (int argc, char *argv[])
  {
    fprintf (stderr, "starting up ...\n");
    caml_startup (argv);
    fprintf (stderr, "acquiring ...\n");
    caml_acquire_runtime_system ();
    fprintf (stderr, "acquired\n");
    // here is where I would be calling an OCaml callback
    // omitted for simplicity
    caml_release_runtime_system ();
    exit (0);
  }
- -

然后用OCaml5的ocaml native compiler编译一下（这里我用的是ocaml-variants.5.0.0+options）：
ocamlopt -g test-ocaml-5.c test.ml -o test-ocaml-5

+

然后用OCaml5的ocaml native compiler编译一下（这里我用的是ocaml-variants.5.0.0+options）：
+ocamlopt -g test-ocaml-5.c test.ml -o test-ocaml-5

运行test-ocaml-5 会出现:

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starting up ...
hello from OCaml
acquiring ...
Fatal error: Fatal error during lock: Resource deadlock avoided

[1]    8998 IOT instruction (core dumped)  ./test-ocaml-5
- -

这里我尝试了一下 4.14.0 和 4.14.1 ， 都没有出现这个情况，而如果用threads编译的话:
ocamlopt -g -I +unix unix.cmxa -I +threads threads.cmxa test-ocaml-5.c test.ml -o test-ocaml-5

+

这里我尝试了一下 4.14.0 和 4.14.1 ， 都没有出现这个情况，而如果用threads编译的话:
+ocamlopt -g -I +unix unix.cmxa -I +threads threads.cmxa test-ocaml-5.c test.ml -o test-ocaml-5

无论在5.0还是4.14.x，都会挂起。

出现这个问题的一个可能原因是，在test-ocaml-5.c中，我在开头调用了caml_startup()，这会让当前线程获取锁，而caml_acquire_runtime_system()会再次获取它，caml_acquire_runtime_system() 应该在caml_release_runtime_system（）之后调用：

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int
main (int argc, char *argv[])
  {
    fprintf (stderr, "starting up ...\n");
    caml_startup (argv);
    fprintf (stderr, "acquiring ...\n");
    caml_release_runtime_system ();
    caml_acquire_runtime_system ();
    fprintf (stderr, "acquired\n");
    exit (0);
  }
-

运行结果为:

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starting up ...
hello from OCaml
acquiring ...
acquired
diff --git "a/2023/06/28/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc/index.html" "b/2023/06/28/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc/index.html" index 3b3b7db7..aba8a0d1 100644 --- "a/2023/06/28/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc/index.html" +++ "b/2023/06/28/\351\232\220\350\227\217\344\270\200\344\272\233OCaml-Effect\347\232\204\346\234\272\345\210\266\357\274\214\350\256\251\345\205\266\350\257\255\346\263\225\345\234\250\347\262\276\347\245\236\344\270\212\346\233\264\346\216\245\350\277\221delimcc/index.html" @@ -192,9 +192,8 @@
-

delimcc_of_fxhandler这个库在OCaml5的effect handlers上实现了一些delimcc原语(shift/reset, control/prompt这些)：

+

delimcc_of_fxhandler这个库在OCaml5的effect handlers上实现了一些delimcc原语(shift/reset, control/prompt这些)：

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let p = new_prompt () in
assert ([] = push_prompt p (fun () ->
               1::2::take_subcont p (fun _k -> [])));
assert ([1;2] = push_prompt p (fun () ->
               1::2::take_subcont p (fun k -> push_subcont k [])));
assert (135 =
  let p1 = new_prompt () in
  let p2 = new_prompt () in
  let p3 = new_prompt () in
  let pushtwice sk =
    sk (fun () ->
      sk (fun () ->
        shift0 p2 (fun sk2 -> sk2 (fun () ->
          sk2 (fun () -> 3))) ()))
   in
   push_prompt p1 (fun () ->
     push_prompt p2 (fun () ->
       push_prompt p3 (fun () -> shift0 p1 pushtwice ()) + 10) + 1) + 100);

print_endline "Success!"
-

另外， avsm这里可以看到一些OCaml的Effect Syntax进展。

还有 multi-shot continuations in OCaml，在这个仓库里面还讨论了一些有趣的问题，例如，OCaml 编译器和runtime会做出一些假设从而进行一些优化，这些优化在使用multi-shot continutation时是不可取的（或完全错误的）。编译器优化导致错误的一个例子是堆到栈的转换，例如:

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(* An illustration of how the heap to stack optimisation is broken.
 * This example is adapted from de Vilhena and Pottier (2021).
 * file: heap2stack.ml
 * compile: ocamlopt -I $(opam var lib)/multicont multicont.cmxa heap2stack.ml
 * run: ./a.out *)

(* We first require a little bit of setup. The following declares an
   operation `Twice' which we use to implement multiple returns. *)
type _ Effect.t += Twice : unit Effect.t

(* The handler `htwice' interprets `Twice' by simply invoking its
   continuation twice. *)
let htwice : (unit, unit) Effect.Deep.handler
  = { retc = (fun x -> x)
    ; exnc = (fun e -> raise e)
    ; effc = (fun (type a) (eff : a Effect.t) ->
      let open Effect.Deep in
      match eff with
      | Twice -> Some (fun (k : (a, _) continuation) ->
         continue (Multicont.Deep.clone_continuation k) ();
         continue k ())
      | _ -> None) }

(* Now for the interesting stuff. In the code below, the compiler will
   perform an escape analysis on the reference `i' and deduce that it
   does not escape the local scope, because it is unaware of the
   semantics of `perform Twice', hence the optimiser will transform
   `i' into an immediate on the stack to save a heap allocation. As a
   consequence, the assertion `(!i = 1)' will succeed twice, whereas
   it should fail after the second return of `perform Twice'. *)
let heap2stack () =
  Effect.Deep.match_with
    (fun () ->
      let i = ref 0 in
      Effect.perform Twice;
      i := !i + 1;
      Printf.printf "i = %d\n%!" !i;
      assert (!i = 1))
    () htwice

(* The following does not trigger an assertion failure. *)
let _ = heap2stack ()

(* To fix this issue, we can wrap reference allocations in an instance
   of `Sys.opaque_identity'. However, this is not really a viable fix
   in general, as we may not have access to the client code that
   allocates the reference! *)
let heap2stack' () =
  Effect.Deep.match_with
    (fun () ->
      let i = Sys.opaque_identity (ref 0) in
      Effect.perform Twice;
      i := !i + 1;
      Printf.printf "i = %d\n%!" !i;
      assert (!i = 1))
    () htwice

(* The following triggers an assertion failure. *)
let _ = heap2stack' ()
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