Re: [Ocamlnet-devel] netmcore: becoming a worker after fork+exec ?

[Gerd S. <in...@ge...>]

Hi Piotr,

I don't think this is even possible. The point is that fork() ensures
that master and worker have the mempool mapped at exactly the same
address (because the mapping is just inherited). If you exec in between,
the mempool is automatically unmapped in the child, and you would have
to map it again. But the process is re-initialized because of the exec,
and it is not sure that the address range is still free (and this is a
real problem, as processes are nowadays initialized with some randomness
to make addresses unpredictable), and so there is no good method to
re-map the mempool at the same address.

So that's the background why there isn't the option of passing file
names or descriptors to Netmcore_mempool.

I don't know what you have in mind, but maybe Netcamlbox is already
sufficient? This module doesn't suffer from this problem, because every
process can here map the shared memory block at different addresses.

Gerd


Am Samstag, den 07.09.2013, 00:16 -0400 schrieb Piotr Mardziel:
> Hello ocamlnet developers,
> 
> Is it possible to establish the master/worker relationship with a process that has been fork+exec'ed (or Netsys_posix.spawn'ed) but is of the same executable as the process doing Netmcore.startup ?
> 
> Let me explain. There is a problem on OSX in that forked child processes cannot access some OS functionality (for example SDL will not work on a forked child process). One has to exec in order to get this functionality back. I would like to be able to communicate with this process (of the same executable if need be) using the convenient netmcore modules but I don't see a way for this process to get a handle on resources managed by the master process. It seems like it is easy to get as far as the getting a handle to the shared memory from which a Netmcore_mempool is created (by simply passing its name as a command argument to exec), but one cannot actually create the resource suitable for interacting with the master and other workers, as far as I can tell.
> 
> Any info about this would be greatly appreciated.
> 
> Best,
> Piotr (Peter) Mardziel <pi...@gm...>
> http://www.cs.umd.edu/~piotrm
> 
> 
> 
> 
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-- 
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Gerd Stolpmann, Darmstadt, Germany    ge...@ge...
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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