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trouble with Marshal.to_string
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Date: -- (:)
From: Anil Madhavapeddy <anil@r...>
Subject: Re: [Caml-list] trouble with Marshal.to_string
On 8 Oct 2005, at 17:35, Norman Ramsey wrote:

>> Are you using any C bindings which create custom blocks?  That error
>> occurs if your custom block does not define a serialization function
>> (documented here: http://caml.inria.fr/pub/docs/manual-ocaml/
>> manual032.html#s:custom).
>>
>
> Thanks; at least now I have some idea what's happening.
>
> I'm not aware of using any C bindings at all, although I am linking
> against the Unix library.  My final executable does contain
> definitions of caml_alloc_custom, caml_register_custom_operations, and
> related functions, but none of my .o or .a files refers to such a
> function.
>
> Any ideas how I might track down the source of a custom block?

The old-fashioned way, with grep :-)  I'm sure there are fancier  
ways, but...

shock:~/src/ocaml-3.08.4 avsm$ grep -r custom_serialize_def *
byterun/custom.c:  ops->serialize = custom_serialize_default;
byterun/custom.h:#define custom_serialize_default NULL
byterun/io.c:  custom_serialize_default,
otherlibs/graph/image.c:  custom_serialize_default,
otherlibs/systhreads/posix.c:  custom_serialize_default,
otherlibs/systhreads/posix.c:  custom_serialize_default,
otherlibs/systhreads/posix.c:  custom_serialize_default,
otherlibs/systhreads/win32.c:  custom_serialize_default,
otherlibs/systhreads/win32.c:  custom_serialize_default,
otherlibs/win32graph/draw.c:        custom_serialize_default,
otherlibs/win32unix/unixsupport.c:  custom_serialize_default,

So it looks like a few functions in the OCaml standard libraries  
aren't serializable; notable the systhreads.  Are you using threads  
in the structures you are marshalling?

Confirmed with a simple test:

let _ =
     let x = Thread.create (fun () -> ()) () in
     Marshal.to_string x [Marshal.Closures]

$ ocamlopt.opt -c -thread t.ml
$ ocamlopt.opt unix.cmxa threads.cmxa -thread -o t t.ml
$ ./t
Fatal error: exception Invalid_argument("output_value: abstract value  
(Custom)")

--
Anil Madhavapeddy                                 http://anil.recoil.org
University of Cambridge                          http://www.cl.cam.ac.uk