A Survey of CPU-GPU Heterogeneous Computing Techniques

https://www.academia.edu/12355899/A_Survey_of_CPU-GPU_Heterogeneous_Computing_Techniques Accepted in ACM Computing Surveys 2015

This paper clearly shows how research on heterogeneous computing has increased greatly in last few years.
Table 3 of this paper summarizes which programming language has been used for GPU and CPU in heterogeneous computing research. Evidently, OpenCL is increasingly being used for programming CPU-GPU heterogeneous systems.