developer-roadmap/src/data/roadmaps/cpp/content/libraries/108-opencl.md

OpenCL

OpenCL (Open Computing Language) is a framework for writing programs that enables you to execute code on heterogeneous platforms consisting of CPUs, GPUs, and other processors. It is primarily used for parallel programming, and it can be employed to improve the performance of various applications, including gaming, image and video rendering, and scientific computing.

Overview

OpenCL provides a standardized programming interface, allowing you to target different devices such as graphics cards from different vendors. You can program in C with OpenCL C or C++ with OpenCL C++ kernel language, which are based on the ISO C99 and C++14 respectively, with specific extensions, built-ins, and features to exploit device parallelism.

Key Concepts

• Platform: A collection of devices and software features provided by a vendor.
• Device: A processing unit that can execute OpenCL code, e.g., a CPU or a GPU.
• Command queue: A sequence of instructions to be executed on a device.
• Kernel: A parallelized function that is executed on OpenCL devices.
• Buffer: A memory object that stores a specific amount of data (e.g., an array of integers or floats) that is accessible by both the host and devices.

Sample Code

Here is a simple OpenCL code example that illustrates how to implement vector addition:

#include <CL/cl.h>
#include <iostream>
#include <vector>

const char *kernelSource = "__kernel void vector_add(__global int *A, __global int *B, __global int *C, const int N){"
                            "  int i = get_global_id(0);"
                            "  if(i < N){"
                            "    C[i] = A[i] + B[i];"
                            "  }"
                            "}";

int main(){
    // Initialize data vectors
    std::vector<int> A = {1, 2, 3};
    std::vector<int> B = {4, 5, 6};
    std::vector<int> C(A.size());

    // Set up OpenCL environment, devices, and context
    // ... omitted for brevity ...

    // Create memory buffers for A, B, and C
    // ... omitted for brevity ...

    // Create kernel from source and set kernel arguments
    // ... omitted for brevity ...

    // Execute kernel using command queue and read output buffer
    // ... omitted for brevity ...

    // Output results
    for (size_t i = 0; i < A.size(); ++i) {
        std::cout << A[i] << " + " << B[i] << " = " << C[i] << std::endl;
    }
    return 0;
}

This code snippet demonstrates the basic structure of an OpenCL program in C++. There are additional details required in order to set up the environment, devices, and context, as well as creating the memory buffers, kernel, and command queue. You can find complete examples and more information in the official OpenCL Programming Guide.