An OpenCLFunction object can be used the same way as a pure function.
The function represented by OpenCLFunction runs in the same process as the Wolfram Language kernel.
The function represented by OpenCLFunction is unloaded when the Wolfram Language kernel exits.
On launch, if the number of threads is not specified (as an extra argument to the OpenCLFunction), then the dimension of the element with largest rank and dimension is chosen. For images, the rank is set to 2.
On launch, if the number of threads is not a multiple of the block dimension, then it is incremented to be a multiple of the block dimension.