1 |
// Barrier version of Jacobi iteration |
2 |
|
3 |
import java.util.concurrent.*; |
4 |
|
5 |
public class FJPhaserJacobi { |
6 |
|
7 |
static int dimGran; |
8 |
|
9 |
static final double EPSILON = 0.0001; // convergence criterion |
10 |
|
11 |
public static void main(String[] args) { |
12 |
int n = 2048; |
13 |
int steps = 1000; |
14 |
try { |
15 |
if (args.length > 0) |
16 |
n = Integer.parseInt(args[0]); |
17 |
if (args.length > 1) |
18 |
steps = Integer.parseInt(args[1]); |
19 |
} |
20 |
|
21 |
catch (Exception e) { |
22 |
System.out.println("Usage: java ThreadPhaserJacobi <matrix size> <max steps>"); |
23 |
return; |
24 |
} |
25 |
|
26 |
ForkJoinPool fjp = new ForkJoinPool(); |
27 |
// int granularity = (n * n / fjp.getParallelism()) / 2; |
28 |
int granularity = n * n / fjp.getParallelism(); |
29 |
dimGran = (int)(Math.sqrt(granularity)); |
30 |
|
31 |
// allocate enough space for edges |
32 |
int dim = n+2; |
33 |
int ncells = dim * dim; |
34 |
double[][] a = new double[dim][dim]; |
35 |
double[][] b = new double[dim][dim]; |
36 |
// Initialize interiors to small value |
37 |
double smallVal = 1.0/dim; |
38 |
for (int i = 1; i < dim-1; ++i) { |
39 |
for (int j = 1; j < dim-1; ++j) |
40 |
a[i][j] = smallVal; |
41 |
} |
42 |
int nreps = 3; |
43 |
for (int rep = 0; rep < nreps; ++rep) { |
44 |
// Fill all edges with 1's. |
45 |
for (int k = 0; k < dim; ++k) { |
46 |
a[k][0] += 1.0; |
47 |
a[k][n+1] += 1.0; |
48 |
a[0][k] += 1.0; |
49 |
a[n+1][k] += 1.0; |
50 |
} |
51 |
Driver driver = new Driver(a, b, 1, n, 1, n, steps); |
52 |
long startTime = System.currentTimeMillis(); |
53 |
fjp.invoke(driver); |
54 |
|
55 |
long time = System.currentTimeMillis() - startTime; |
56 |
double secs = ((double)time) / 1000.0; |
57 |
|
58 |
System.out.println("Compute Time: " + secs); |
59 |
System.out.println(fjp); |
60 |
|
61 |
} |
62 |
|
63 |
} |
64 |
|
65 |
static class Segment extends CyclicAction { |
66 |
double[][] A; // matrix to get old values from |
67 |
double[][] B; // matrix to put new values into |
68 |
// indices of current submatrix |
69 |
final int loRow; |
70 |
final int hiRow; |
71 |
final int loCol; |
72 |
final int hiCol; |
73 |
volatile double maxDiff; // maximum difference between old and new values |
74 |
|
75 |
Segment(double[][] A, double[][] B, |
76 |
int loRow, int hiRow, |
77 |
int loCol, int hiCol, |
78 |
Phaser br) { |
79 |
super(br); |
80 |
this.A = A; this.B = B; |
81 |
this.loRow = loRow; this.hiRow = hiRow; |
82 |
this.loCol = loCol; this.hiCol = hiCol; |
83 |
} |
84 |
|
85 |
public void step() { |
86 |
maxDiff = update(A, B); |
87 |
double[][] tmp = A; A = B; B = tmp; |
88 |
} |
89 |
|
90 |
double update(double[][] a, double[][] b) { |
91 |
double md = 0.0; // local for computing max diff |
92 |
|
93 |
for (int i = loRow; i <= hiRow; ++i) { |
94 |
for (int j = loCol; j <= hiCol; ++j) { |
95 |
double v = 0.25 * (a[i-1][j] + a[i][j-1] + |
96 |
a[i+1][j] + a[i][j+1]); |
97 |
b[i][j] = v; |
98 |
|
99 |
double diff = v - a[i][j]; |
100 |
if (diff < 0) diff = -diff; |
101 |
if (diff > md) md = diff; |
102 |
} |
103 |
} |
104 |
|
105 |
return md; |
106 |
} |
107 |
|
108 |
} |
109 |
|
110 |
static class MyPhaser extends Phaser { |
111 |
final int max; |
112 |
MyPhaser(int steps) { this.max = steps - 1; } |
113 |
public boolean onAdvance(int phase, int registeredParties) { |
114 |
return phase >= max || registeredParties <= 0; |
115 |
} |
116 |
} |
117 |
|
118 |
static class Driver extends RecursiveAction { |
119 |
double[][] A; // matrix to get old values from |
120 |
double[][] B; // matrix to put new values into |
121 |
final int loRow; // indices of current submatrix |
122 |
final int hiRow; |
123 |
final int loCol; |
124 |
final int hiCol; |
125 |
final int steps; |
126 |
Driver(double[][] mat1, double[][] mat2, |
127 |
int firstRow, int lastRow, |
128 |
int firstCol, int lastCol, |
129 |
int steps) { |
130 |
|
131 |
this.A = mat1; this.B = mat2; |
132 |
this.loRow = firstRow; this.hiRow = lastRow; |
133 |
this.loCol = firstCol; this.hiCol = lastCol; |
134 |
this.steps = steps; |
135 |
} |
136 |
|
137 |
public void compute() { |
138 |
int rows = hiRow - loRow + 1; |
139 |
int cols = hiCol - loCol + 1; |
140 |
int rblocks = (int)(Math.round((float)rows / dimGran)); |
141 |
int cblocks = (int)(Math.round((float)cols / dimGran)); |
142 |
|
143 |
int n = rblocks * cblocks; |
144 |
|
145 |
System.out.println("Using " + n + " segments"); |
146 |
|
147 |
Segment[] segs = new Segment[n]; |
148 |
Phaser barrier = new MyPhaser(steps); |
149 |
int k = 0; |
150 |
for (int i = 0; i < rblocks; ++i) { |
151 |
int lr = loRow + i * dimGran; |
152 |
int hr = lr + dimGran; |
153 |
if (i == rblocks-1) hr = hiRow; |
154 |
|
155 |
for (int j = 0; j < cblocks; ++j) { |
156 |
int lc = loCol + j * dimGran; |
157 |
int hc = lc + dimGran; |
158 |
if (j == cblocks-1) hc = hiCol; |
159 |
|
160 |
segs[k] = new Segment(A, B, lr, hr, lc, hc, barrier); |
161 |
++k; |
162 |
} |
163 |
} |
164 |
invokeAll(segs); |
165 |
double maxd = 0; |
166 |
for (k = 0; k < n; ++k) { |
167 |
double md = segs[k].maxDiff; |
168 |
if (md > maxd) maxd = md; |
169 |
} |
170 |
System.out.println("Max diff after " + steps + " steps = " + maxd); |
171 |
} |
172 |
} |
173 |
} |
174 |
|