Introduction

Many I/O thorns output data from distributed CCTK array variables. If - in a multiprocessor run - output is done by only one processor, it needs to collect the data from the others. This ties the I/O thorn to the driver since it has to know about domain-decomposed data layout, interprocessor ghostzones, etc.

A clean way of separating the I/O code from the driver is to use a thorn which provides a generic interface to get/put the distributed data on/from the I/O processor for writing/reading. This interface can also provide more features such as downsampling, datatype conversions, or hyperslab selections. A hyperslab is defined in this context a subset of a global CCTK array, with its own dimension, origin, direction, and extents.

Another possible use of hyperslabs is the implementation of certain boundary conditions (e.g. reflection). By having the boundary condition code calling generic hyperslab get/put calls, it can be written without special knowledge about driver specifics.

This thorn documentation describes the complete generic hyperslab API. All routines use CCTK data types in their argument lists and as return codes exclusively. This allows actual implementations of this API to be realized as CCTK function aliases. Different hyperslab thorns can then implementing the API using the same function names, and other thorns using the API can be independent of the actual hyperslab thorns which are compiled in.

The current version of thorn PUGHSlab implements only parts of the CCTK hyperslab API. Please refer to section I4.4 for implementation details.