Plugins are loaded dynamically based upon configuration parameters and
user options. It isn't even possible with the current code to link
everything at build time due to conflicting symbol names (slurm can
run several plugins of the same type all having the same symbols).
----- Forwarded message from sebgr...@cs.umu.se -----
Date: Mon, 12 Mar 2012 04:00:07 -0600
From: Sebastian Gröhn <sebgr...@cs.umu.se>
Reply-To: slurm-dev <slurm-dev@schedmd.com>
Subject: [slurm-dev] Plugin loading -- local or global mode linking
To: slurm-dev <slurm-dev@schedmd.com>
Hi!
When trying to adapt GridScheduler's (former SGE) Java DRMAA wrappers to
Slurms C DRMAA plugin, I have discovered something peculiar about the way
Slurm's plugins (for authenticaction, etc.) are loaded:
When using Slurm's libdrmaa.so and its example C program, everything is
working correctly. But when trying to run another test program from Java with
a JNI wrapper library to libdrmaa, I get "undefined symbol" errors in
auth_munge.so for symbols defined in libslurm.so.
After some digging, I think I understand why this is: I use Munge for
authentication and when libslurm.so is used it tries to load auth_munge.so. It
is loaded at run-time (with ldopen(...) ) and in turn uses symbols from
libslurm.so, but without linking to it. The way this seems to function in the
regular pure-C way is that libslurm is loaded in "global mode" (the
RTLD_GLOBAL flag to ldopen, or equivalent), making all symbols in it available
implicilty. Hence it works. But from JNI, it is loaded in "local mode"
(RTLD_LOCAL) and hence auth_munge cannot find the symbols from libslurm. The
same issue seems to exist in most plugins.
Is there some reason for why the plugins are not linked to libslurm when
built, or is my build not configured correctly? Else, it would seem that
library files should link to all other libraries they use.
(There seems to be a way to force libslurm to be loaded in global mode, by
explicitly loading libdrmaa (which in turn loads libslurm) in the JNI on-load
hook, but I don't now id this has any consequences I haven't discovered
yet...)
Regards,
/Sebastian Gröhn
---
Sebastian Gröhn, Research Assistant
Dept. of Computing Science, Umeå University
----- End forwarded message -----
