[Libguestfs] [PATCH libnbd 6/7] python: Use free callback to free closure root.

[Eric Blake]

On 8/12/19 11:08 AM, Richard W.M. Jones wrote:
> Same as the previous commit, but for Python.
> ---
>  generator/generator | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 

> @@ -4454,6 +4451,11 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
>         pr "    PyErr_SetString (PyExc_TypeError,\n";
>         pr "                     \"callback parameter %s is not callable\");\n" cbname;
>         pr "    return NULL;\n";
> +       pr "  }\n";
> +       pr "  if (nbd_add_free_callback (h, %s_user_data,\n" cbname;
> +       pr "                             decref, NULL) == -1) {\n";
> +       pr "    PyErr_NoMemory ();\n";
> +       pr "    return NULL;\n";
>         pr "  }\n"
>      | Enum _ -> ()
>      | Flags (n, _) -> pr "  %s_u32 = %s;\n" n n
> @@ -4600,6 +4602,12 @@ let generate_python_methods_c () =
>    pr "\n";
>    pr "#include <methods.h>\n";
>    pr "\n";
> +  pr "static void\n";
> +  pr "decref (void *ptr, void *user_data)\n";
> +  pr "{\n";
> +  pr "  Py_DECREF (ptr);\n";
> +  pr "}\n";

Well, in the OCaml case, you were actively using the fact that ptr and
user_data might be different, and freeing the second; where in the
Python case you are only ever caring about the ptr argument and always
passing NULL for the second (meaning you had to write a shim around
Py_DecRef, as hidden under the Py_DECREF macro).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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