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// Barrier version of Jacobi iteration |
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import java.util.concurrent.*; |
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public class FJPhaserJacobi { |
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static int dimGran; |
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static final double EPSILON = 0.0001; // convergence criterion |
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public static void main(String[] args) { |
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int n = 2048; |
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int steps = 1000; |
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try { |
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if (args.length > 0) |
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n = Integer.parseInt(args[0]); |
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if (args.length > 1) |
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steps = Integer.parseInt(args[1]); |
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} |
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catch (Exception e) { |
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System.out.println("Usage: java ThreadPhaserJacobi <matrix size> <max steps>"); |
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return; |
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} |
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|
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ForkJoinPool fjp = new ForkJoinPool(); |
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// int granularity = (n * n / fjp.getParallelism()) / 2; |
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int granularity = n * n / fjp.getParallelism(); |
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dimGran = (int)(Math.sqrt(granularity)); |
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|
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// allocate enough space for edges |
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int dim = n+2; |
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int ncells = dim * dim; |
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double[][] a = new double[dim][dim]; |
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double[][] b = new double[dim][dim]; |
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// Initialize interiors to small value |
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double smallVal = 1.0/dim; |
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for (int i = 1; i < dim-1; ++i) { |
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for (int j = 1; j < dim-1; ++j) |
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a[i][j] = smallVal; |
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} |
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int nreps = 3; |
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for (int rep = 0; rep < nreps; ++rep) { |
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// Fill all edges with 1's. |
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for (int k = 0; k < dim; ++k) { |
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a[k][0] += 1.0; |
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a[k][n+1] += 1.0; |
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a[0][k] += 1.0; |
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a[n+1][k] += 1.0; |
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} |
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Driver driver = new Driver(a, b, 1, n, 1, n, steps); |
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long startTime = System.currentTimeMillis(); |
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fjp.invoke(driver); |
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long time = System.currentTimeMillis() - startTime; |
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double secs = ((double)time) / 1000.0; |
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System.out.println("Compute Time: " + secs); |
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System.out.println(fjp); |
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} |
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} |
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static class Segment extends CyclicAction { |
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double[][] A; // matrix to get old values from |
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double[][] B; // matrix to put new values into |
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// indices of current submatrix |
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final int loRow; |
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final int hiRow; |
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final int loCol; |
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final int hiCol; |
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volatile double maxDiff; // maximum difference between old and new values |
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Segment(double[][] A, double[][] B, |
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int loRow, int hiRow, |
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int loCol, int hiCol, |
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Phaser br) { |
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super(br); |
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this.A = A; this.B = B; |
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this.loRow = loRow; this.hiRow = hiRow; |
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this.loCol = loCol; this.hiCol = hiCol; |
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} |
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public void step() { |
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maxDiff = update(A, B); |
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double[][] tmp = A; A = B; B = tmp; |
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} |
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double update(double[][] a, double[][] b) { |
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double md = 0.0; // local for computing max diff |
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for (int i = loRow; i <= hiRow; ++i) { |
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for (int j = loCol; j <= hiCol; ++j) { |
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double v = 0.25 * (a[i-1][j] + a[i][j-1] + |
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a[i+1][j] + a[i][j+1]); |
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b[i][j] = v; |
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double diff = v - a[i][j]; |
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if (diff < 0) diff = -diff; |
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if (diff > md) md = diff; |
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} |
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} |
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return md; |
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} |
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} |
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static class MyPhaser extends Phaser { |
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final int max; |
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MyPhaser(int steps) { this.max = steps - 1; } |
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public boolean onAdvance(int phase, int registeredParties) { |
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return phase >= max || registeredParties <= 0; |
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} |
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} |
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static class Driver extends RecursiveAction { |
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double[][] A; // matrix to get old values from |
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double[][] B; // matrix to put new values into |
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final int loRow; // indices of current submatrix |
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final int hiRow; |
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final int loCol; |
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final int hiCol; |
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final int steps; |
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Driver(double[][] mat1, double[][] mat2, |
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int firstRow, int lastRow, |
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int firstCol, int lastCol, |
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int steps) { |
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this.A = mat1; this.B = mat2; |
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this.loRow = firstRow; this.hiRow = lastRow; |
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this.loCol = firstCol; this.hiCol = lastCol; |
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this.steps = steps; |
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} |
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public void compute() { |
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int rows = hiRow - loRow + 1; |
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int cols = hiCol - loCol + 1; |
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int rblocks = (int)(Math.round((float)rows / dimGran)); |
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int cblocks = (int)(Math.round((float)cols / dimGran)); |
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int n = rblocks * cblocks; |
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System.out.println("Using " + n + " segments"); |
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Segment[] segs = new Segment[n]; |
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Phaser barrier = new MyPhaser(steps); |
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int k = 0; |
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for (int i = 0; i < rblocks; ++i) { |
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int lr = loRow + i * dimGran; |
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int hr = lr + dimGran; |
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if (i == rblocks-1) hr = hiRow; |
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|
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for (int j = 0; j < cblocks; ++j) { |
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int lc = loCol + j * dimGran; |
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int hc = lc + dimGran; |
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if (j == cblocks-1) hc = hiCol; |
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segs[k] = new Segment(A, B, lr, hr, lc, hc, barrier); |
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++k; |
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} |
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} |
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invokeAll(segs); |
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double maxd = 0; |
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for (k = 0; k < n; ++k) { |
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double md = segs[k].maxDiff; |
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if (md > maxd) maxd = md; |
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} |
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System.out.println("Max diff after " + steps + " steps = " + maxd); |
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} |
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} |
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} |
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