[Users] Optional capabilities

[Ian Hinder]

On 30 Nov 2010, at 02:24, Erik Schnetter wrote:

>> 1. Do we want all capabilities to generate automatically a preprocessor macro which can be checked?  e.g. HAVE_CAPABILITY_HDF5, (to avoid conflicts with  autoconf-generated macros)
> 
> Yes, this should be the case.
> 
>> 2. If not, then we could add the BEGIN_DEFINE...END_DEFINE lines above to HDF5.sh to manually set the define.
> 
> I don't mind whether it is automatic or whether the scripts provide this.

It is easy to add to the script, so I vote for it being automatic.

>> 3. I think line 166 of CreateConfigurationBindings.pl should be removed.
> 
> Could be -- do you want to post a patch? Or is this the line that
> needs to be corrected to generate the #defines automatically?

It could be modified to do that, or the required line could be added to the header file of the providing thorn.  I think it is more natural to do the latter, since then it would only be added in one place rather than in each thorn that requires the capability.

I attach a patch which:

* Adds a line such as

	#define HAVE_CAPABILITY_<cap> 1

where <cap> is the capability name, to the Capabilities/cctki_<cap>.h file.  This is the file that is later included by any thorns which require the capability.

* Removes the incorrect line which breaks compilation of cctki_Capabilities.h and does not do what looks like was intended.

>> 4. There should be some mechanism for each thorn to include cctki_Capabilities.h automatically.
> 
> Yes, definitely. It should probably be part of cctk.h.


I'm not sure about the Cactus conventions for this.  There aren't any other cctki_ headers included from cctk.h.  The problem with including cctki_Capabilities.h in cctk.h is that when this file is modified, for example when a thorn is added or removed, every source file in the configuration would need to be recompiled.  One way around this would be to exclude cctki_Capabilities.h from all thorns' dependencies, as is done with cctk_Arguments.h.  However, this would mean that when a new thorn providing a capability was added, the thorns requiring this capability would not be recompiled.  My best solution would be to have something like

	#include "../Configuration/Thorns/cctki_" CCTK_THORNSTRING ".h"

in cctk.h.  However, I can't get this to work.  String concatenation happens after preprocessing, and there is no preprocessor operator to concatenate two string literals (the ## operator only works on identifiers, not strings).

The best solution I can get to work is to have all thorns which optionally require capabilities include their corresponding "../Configuration/Thorns/cctki_<thornname>.h" file manually.

-- 
Ian Hinder
ian.hinder at aei.mpg.de
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