opencl

OpenCL SDK

Version: v2026.05.29 (Khronos Group OpenCL-SDK) Language: C (OpenCL 1.0–3.1) / C++ (opencl.hpp wrapper) License: Apache-2.0 Repo: https://github.com/KhronosGroup/OpenCL-SDK

Overview

OpenCL (Open Computing Language) is a framework for parallel programming across heterogeneous platforms — GPUs, CPUs, FPGAs, and DSPs — from a single API. The SDK bundles:

• OpenCL-Headers — C headers (<CL/cl.h>, <CL/cl_ext.h>)
• OpenCL-CLHPP — C++ wrapper (<CL/opencl.hpp>)
• OpenCL-ICD-Loader — runtime dispatch to installed platform drivers
• OpenCLUtils / OpenCLSDK — utility libraries (<CL/Utils/>, <CL/SDK/>)

Quick Start (C)

Kernel file saxpy.cl:

__kernel void saxpy(float a, __global float *x, __global float *y) {
    int i = get_global_id(0);
    y[i] = fma(a, x[i], y[i]);
}

Host:

#include <CL/cl.h>
cl_platform_id plat; cl_device_id dev;
clGetPlatformIDs(1, &plat, NULL);
clGetDeviceIDs(plat, CL_DEVICE_TYPE_DEFAULT, 1, &dev, NULL);
cl_context ctx = clCreateContext(NULL, 1, &dev, NULL, NULL, &err);
cl_command_queue q = clCreateCommandQueueWithProperties(ctx, dev, NULL, &err);
// ... load source, clCreateProgramWithSource, clBuildProgram,
//     clCreateKernel, clSetKernelArg, clEnqueueNDRangeKernel,
//     clEnqueueReadBuffer, clReleaseXxx ...

Quick Start (C++)

#define CL_HPP_ENABLE_EXCEPTIONS
#define CL_HPP_TARGET_OPENCL_VERSION 300   // default is now 310 (OpenCL 3.1); minimum 200
#include <CL/opencl.hpp>

cl::Context ctx{CL_DEVICE_TYPE_DEFAULT};
cl::Device  dev = ctx.getInfo<CL_CONTEXT_DEVICES>()[0];
cl::CommandQueue queue{ctx, dev};
cl::Program prog{ctx, source_string};
prog.build(dev);
auto saxpy = cl::KernelFunctor<cl_float, cl::Buffer, cl::Buffer>(prog, "saxpy");
saxpy(cl::EnqueueArgs{queue, cl::NDRange{N}}, a, buf_x, buf_y);

Core Concepts

• Work-item — one parallel execution unit; maps to one GPU thread
• Work-group — block of work-items sharing local memory and barriers
• NDRange — N-dimensional index space (up to 3D); defines total parallelism
• Context — owns devices, memory objects, programs, and queues
• Command Queue — ordered or OOO stream of commands to one device
• Memory object — buffer (linear) or image (typed, sampled); device-side
• Kernel — a __kernel function compiled from OpenCL C source or SPIR-V
• Event — synchronization token returned by every enqueue command
• Address spaces — __global (buffers), __local (shared), __constant (read-only), __private (per-item)