JOCL Tutorial

Hello JOCL host program: import com.jogamp.opencl.*; import java.io.IOException; import java.nio.FloatBuffer; import java.util.Random;

import static java.lang.System.*; import static com.jogamp.opencl.CLMemory.Mem.*;

/** * Hello Java OpenCL example. Adds all elements of buffer A to buffer B * and stores the result in buffer C. * Sample was inspired by the Nvidia VectorAdd example written in C/C++ * which is bundled in the Nvidia OpenCL SDK. * @author Michael Bien */ public class HelloJOCL {

public static void main(String[] args) throws IOException {

int elementCount = 11444777;   // Length of arrays to process int localWorkSize = 256;       // Local work size int globalWorkSize = roundUp(localWorkSize, elementCount); // rounded up to the nearest multiple of the localWorkSize

// set up       CLContext context = CLContext.create; CLProgram program = context.createProgram(HelloJOCL.class.getResourceAsStream("VectorAdd.cl")).build;

CLBuffer clBufferA = context.createFloatBuffer(globalWorkSize, READ_ONLY); CLBuffer clBufferB = context.createFloatBuffer(globalWorkSize, READ_ONLY); CLBuffer clBufferC = context.createFloatBuffer(globalWorkSize, WRITE_ONLY);

// fill read buffers with random numbers. fillBuffer(clBufferA.getBuffer, 12345); fillBuffer(clBufferB.getBuffer, 67890);

// get a reference to the kernel functon with the name 'VectorAdd' // and map the buffers to its input parameters. CLKernel kernel = program.createCLKernel("VectorAdd"); kernel.putArgs(clBufferA, clBufferB, clBufferC).putArg(elementCount);

// create command queue on fastest device. CLCommandQueue queue = context.getMaxFlopsDevice.createCommandQueue;

// asynchronous write of data to GPU device, // blocking read later to get the computed results back. long time = nanoTime; queue.putWriteBuffer(clBufferA, false) .putWriteBuffer(clBufferB, false) .put1DRangeKernel(kernel, 0, globalWorkSize, localWorkSize) .putReadBuffer(clBufferC, true); time = nanoTime - time;

// cleanup all resources associated with this context. context.release;

// print first few elements of the resulting buffer to the console. out.println("a+b=c results snapshot: "); for(int i = 0; i < 10; i++) out.print(clBufferC.getBuffer.get + ", "); out.println("...; " + clBufferC.getBuffer.remaining + " more");

out.println("computation took: "+(time/1000000)+"ms"); }

/* utilities */ private static void fillBuffer(FloatBuffer buffer, int seed) { Random rnd = new Random(seed); while(buffer.remaining != 0) buffer.put(rnd.nextFloat*100); buffer.rewind; }

private static int roundUp(int groupSize, int globalSize) { int r = globalSize % groupSize; if (r == 0) return globalSize; else       return globalSize + groupSize - r;    } } Hello JOCL Kernel: // OpenCL Kernel Function for element by element vector addition kernel void VectorAdd(global const float* a, global const float* b, global float* c, int numElements) {

// get index into global data array int iGID = get_global_id(0);

// bound check, equivalent to the limit on a 'for' loop if (iGID >= numElements) { return; }

// add the vector elements c[iGID] = a[iGID] + b[iGID]; }