Which book on OpenCl do people here rate ?
OpenCL is indeed a fast moving target at the moment, and the books may become quickly out of date.
As an introduction, "Hands On OpenCL" course/materials (slides, exercises, and solutions) by Simon McIntosh-Smith and Tom Deakin is the way to go: http://handsonopencl.github.io/
Keep track of the International Workshop on OpenCL (IWOCL) to learn more and stay up to date: http://www.iwocl.org/iwocl-2017/conference-program/
Here's the program from last year: http://www.iwocl.org/iwocl-2016/iwocl-2016-sessions/
For instance, the Boost Compute library, http://www.boost.org/libs/compute/
(in Boost since version 1.61.0) has been presented there: http://www.iwocl.org/wp-content/uploads ... ompute.pdf