Re: [Caml-list] Native dynlink and reloading modules

["Richard W.M. Jones" <rich@annexia.org>]

On Thu, Mar 22, 2012 at 01:51:57PM +0100, Alain Frisch wrote:
> On 03/22/2012 12:47 PM, Richard W.M. Jones wrote:
> >
> >I'm a bit surprised to find that native dynlink doesn't work in the
> >same way as bytecode dynlink in respect to reloading the same module.
> >(See attached test program)
> >
> >In bytecode dynlink, reloading (ie. Dynlink.loadfile) the same module
> >causes the new module code to override the old module code:
> >
> >   $ ./dynlink_test
> >   testing bytecode ...
> >   a
> >   b
> >
> >But in native dynlink, the new module is silently discarded and the
> >old code appears to run:
> >
> >   $ ./dynlink_test
> >   testing native ...
> >   a
> >   a
> >
> >I would classify this as a bug, but I'm not quite sure what is
> >expected to happen.  Is there some other way to override a module as
> >in bytecode?
> 
> natdynlink currenlty depends on the OS dynamic linker, we cannot
> control the semantics so precisely (you can try loadfile_private,
> but I'm not sure it would solve your issue).

This is all a bit, umm, unexpected.

Stepping back, the problem I'm trying to solve is how to reload a
configuration-like file into a daemon without restarting the daemon.
The "configuration-like file" is the whenjobs jobs script[1], and the
daemon is the whenjobs daemon[2].

Any ideas on how best to go about this?  Note that the whenjobs jobs
script is intentionally a Turing-complete OCaml program, so converting
it to another format is probably not going to be practical.

Rich.

[1] examples:
    http://git.annexia.org/?p=whenjobs.git;a=blob;f=tests/jobs/t201_ocaml_set_variable.ml;hb=HEAD
    http://people.redhat.com/~rjones/whenjobs/whenjobs.txt

[2] http://git.annexia.org/?p=whenjobs.git;a=blob;f=daemon/daemon.ml;h=bc4f51a2f1177e5be2692a233d7f2b850f9a55bc;hb=HEAD#l293

-- 
Richard Jones
Red Hat