取消 Lwt。线

Question

我这辈子都找不到处理取消 lwt 线程的方法。

这是我的简化版。

#require "lwt.unix, lwt.ppx"
open Lwt.Infix

let program =
  let counter = ref 1 in
  let can_cancel = fst (Lwt.task ()) in

  Lwt.async_exception_hook := (fun _ ->
    prerr_endline "some exception");

  Lwt.on_cancel can_cancel (fun () ->
            Lwt_io.printl "correct ending" |> Lwt.ignore_result);

  Lwt.async begin fun () ->
    let rec forever () =

      try%lwt
        Lwt_io.printl "Hello World" >>= fun () ->

        if !counter = 3 then Lwt.cancel can_cancel
        else counter := !counter + 1;
        Lwt_unix.sleep 0.5 >>= forever
      with
        Lwt.Canceled -> Lwt_io.printl "canceled inside function"
    in

    Lwt.catch forever begin function
      | Lwt.Canceled -> Lwt_io.printl "Cancled exception happened"
      | _ -> Lwt.return ()
    end
  end;
  can_cancel

let () =
  Lwt_main.run program

您可以看到我多次尝试捕捉已取消的异常，none 成功了。我的输出是

utop cancelable.ml                                                     ⏎
Hello World
Hello World
Hello World
correct ending
Exception: Lwt.Canceled.

在更宏大的计划中，我有一个 unit Lwt.t list ref，它是用 Lwt.task 创建的，然后我计划在列表上做 List.iter Lwt.cancel，然后将其替换为unit Lwt.t

类型的新线程

Answer 1

我把 try/with 放在了错误的级别。

此代码显示了为 Lwt.Canceled 异常

放置 try/with 的正确位置

#require "lwt.unix, lwt.ppx"
open Lwt.Infix

let program =
  let counter = ref 1 in
  let can_cancel = fst (Lwt.task ()) in

  Lwt.async begin fun () ->
    let rec forever () =
        Lwt_io.printl "Hello World" >>= fun () ->
        if !counter = 3 then Lwt.cancel can_cancel
        else counter := !counter + 1;
        Lwt_unix.sleep 0.5 >>= forever
    in
    forever ()
  end;
  can_cancel

let () =
  try
    Lwt_main.run program
  with
    Lwt.Canceled -> Lwt_io.printl "ended" |> Lwt.ignore_result

取消 Lwt。线

Canceling a Lwt. thread

multithreading

ocaml

lwt