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% $Header$
% This file contains documentation for features which aren't implemented
% yet, and which are far enough in the future that I (Jonathan) decided
% to remove them from documentation.tex for the time being.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Caching}
\label{sect-generic-options/caching}
Some interpolators may support special ``caching'' optimizations to
speed repeated interpolations where some or all of the interpolator
arguments and/or parameters are the same. For example, when interpolating
a tabulated equation of state the number of dimensions, the coordinate
origin and grid spacing, and the input arrays (the tabulated equation
of state data), will probably all be the same from one interpolator
call to another.
If an interpolator supports caching, the following parameters should
be used to control this:
\begin{verbatim}
const char cache_type[]; /* set with Util_TableSetString() */
const char cache_control[]; /* set with Util_TableSetString() */
CCTK_INT cache_handle;
\end{verbatim}
There are three basic operations supported:
\begin{description}
\item[Create a Cache]
To set up caching, call the interpolator with \verb|cache_type|
set to describe what arguments and/or parameters will remain
the same in future interpolator calls, \verb|cache_control|
set to the string \verb|"create"|, and \verb|cache_handle|
{\em not\/} in the parameter table. The interpolator will
then do extra (possibly quite time-consuming) work to set
up cached information. The interpolator will delete the
key \verb|cache_control|, and return a handle to the cached
information in \verb|cache_handle|; this allows multiple caches
to be active concurrently.
\item[Use a Cache]
To use a cache (\ie{} to make an interpolation with the
hoped-for speedup), just call the interpolator with
\verb|cache_handle| set to the value returned when the cache
was created. Note that you still have to provide all the
``will be the same'' interpolator arguments and/or parameters;
providing a cache handle is essentially just a promise that
these will be the same as in the cache-create interpolator
call. The details of what information is cached, and if/how
the ``will be the same'' arguments are still used, are up to
the interpolator.
\item[Destroy a Cache]
To destroy a cache (\ie{} free any memory allocated when
the cache was created), call the interpolator with
\verb|cache_handle| set to the value returned when the cache
was created, and \verb|cache_control| set to the string
\verb|"destroy"|. The interpolator will delete the keys
\verb|cache_handle| and \verb|cache_control|, and destroy
the cache.
\end{description}
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