Use shared libraries in Cactus

[Erik Schnetter]

I tend to have a single thorn list with many thorns. Building executables is slow, and much time is spent in the final link stage. With shared libraries, this time could be much reduced. Using shared libraries seems to be simple on many architectures; there are either ld flags one can use, or one could use libtool for the implementation.

This would also be a first step towards building thorns (or external libraries) independently of each other.

Keyword:

[Frank Löffler]

That would be nice indeed. However, it would require a bit of infrastructure, especially on simfactory scripts. One issue with a 'split' executable would be that all libraries would need to be accessible on the compute nodes, so simfactory would need to copy them into the job directories and use these (also for consistency reasons). In addition, for startup of large jobs it is usually good to "pre-load" the executable into memory before starting the job. This would also need to be done for all libraries, which isn't that difficult but would need to be done.

We should have at least the library-copy in place before we enable this. There might be other issues as well, but I cannot think of something else right now.