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From: Tom Ridge <tom.j.ridge+caml@googlemail.com>
Date: Fri, 27 Sep 2013 11:10:02 +0100
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Message-ID: <CABooLwPwdN+g4Aor4O=Dfm5+zmOnRqnaRcaN5BCHTW4s4gZoZQ@mail.gmail.com>
To: caml-list <caml-list@inria.fr>
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Subject: [Caml-list] Thread behaviour

Dear caml-list,

I have a little program which creates a thread, and then sits in a loop:

--

let f () =
  let _ = ignore (print_endline "3") in
  let _ = ignore (print_endline "hello") in
  let _ = ignore (print_endline "4") in
  ()

let main () =
  let _ = ignore (print_endline "1") in
  let t = Thread.create f () in
  (* let _ = Thread.join t in *)
  let _ = ignore (print_endline "2") in
  while true do
    flush stdout;
  done

let _ = main ()

--

I compile the program with the following Makefile clause:

test.byte: test.ml FORCE
ocamlc -o $@ -thread unix.cma threads.cma $<

When I run the program I get the output:

1
2

and the program then sits in the loop. I was expecting the output from
f to show up as well. If you wait a while, it does. But you have to
wait quite a while.

What am I doing wrong here? I notice that if I put Thread.yield in the
while loop then f's output gets printed pretty quickly. But why should
the while loop affect scheduling of f's thread?

Thanks