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1
3 import EDU.oswego.cs.dl.util.concurrent.*;
4
5 public class BarrierJacobi {
6
7 static final int DEFAULT_GRANULARITY = 128;
8
9
13
14 static int granularity = DEFAULT_GRANULARITY;
15
16 static final double EPSILON = 0.001;
18
19 public static void main(String  [] args) {
20 try {
21 int n;
22 int steps;
23 try {
24 n = Integer.parseInt(args[0]);
25 steps = Integer.parseInt(args[1]);
26 if (args.length > 2) granularity = Integer.parseInt(args[2]);
27 }
28
29 catch (Exception e) {
30 System.out.println("Usage: java BarrierJacobi <matrix size> <max steps> [<granularity>]");
31 return;
32 }
33
34
36 double[][] a = new double[n+2][n+2];
37 double[][] b = new double[n+2][n+2];
38
39
40
43 for (int k = 0; k < n+2; ++k) {
44 a[k][0] = 1.0;
45 a[k][n+1] = 1.0;
46 a[0][k] = 1.0;
47 a[n+1][k] = 1.0;
48
49 b[k][0] = 1.0;
50 b[k][n+1] = 1.0;
51 b[0][k] = 1.0;
52 b[n+1][k] = 1.0;
53 }
54
55 long startTime = System.currentTimeMillis();
56
57 new Driver(a, b, 1, n, 1, n, steps).compute();
58
59 long time = System.currentTimeMillis() - startTime;
60 double secs = ((double)time) / 1000.0;
61
62 System.out.println("Compute Time: " + secs);
63
64 }
65 catch (InterruptedException ex) {}
66 }
67
68 static class Segment implements Runnable {
69
70 double[][] A; double[][] B;
73 final int loRow;
75 final int hiRow;
76 final int loCol;
77 final int hiCol;
78 final int steps;
79 final CyclicBarrier barrier;
80
81 final Segment[] allSegments;
82
83 volatile double maxDiff; volatile boolean converged = false;
85
86 Segment(double[][] A, double[][] B,
87 int loRow, int hiRow,
88 int loCol, int hiCol,
89 int steps,
90 CyclicBarrier barrier,
91 Segment[] allSegments) {
92 this.A = A; this.B = B;
93 this.loRow = loRow; this.hiRow = hiRow;
94 this.loCol = loCol; this.hiCol = hiCol;
95 this.steps = steps;
96 this.barrier = barrier;
97 this.allSegments = allSegments;
98 }
99
100 void convergenceCheck(int step) {
101 for (int i = 0; i < allSegments.length; ++i)
102 if (allSegments[i].maxDiff > EPSILON) return;
103
104 System.out.println("Converged after " + step + " steps");
105
106 for (int i = 0; i < allSegments.length; ++i)
107 allSegments[i].converged = true;
108 }
109
110
111 public void run() {
112 try {
113 double[][] a = A;
114 double[][] b = B;
115
116 for (int i = 1; i <= steps && !converged; ++i) {
117 maxDiff = update(a, b);
118
119 int index = barrier.barrier();
120 if (index == 0) convergenceCheck(i);
121 barrier.barrier();
122
123 double[][] tmp = a; a = b; b = tmp;
124 }
125 }
126 catch(Exception ex) {
127 return;
128 }
129 }
130
131 double update(double[][] a, double[][] b) {
132 double md = 0.0;
134 for (int i = loRow; i <= hiRow; ++i) {
135 for (int j = loCol; j <= hiCol; ++j) {
136 double v = 0.25 * (a[i-1][j] + a[i][j-1] +
137 a[i+1][j] + a[i][j+1]);
138 b[i][j] = v;
139
140 double diff = v - a[i][j];
141 if (diff < 0) diff = -diff;
142 if (diff > md) md = diff;
143 }
144 }
145
146 return md;
147 }
148
149 }
150
151
152 static class Driver {
153 double[][] A; double[][] B;
156 final int loRow; final int hiRow;
158 final int loCol;
159 final int hiCol;
160 final int steps;
161
162 Driver(double[][] mat1, double[][] mat2,
163 int firstRow, int lastRow,
164 int firstCol, int lastCol,
165 int steps) {
166
167 this.A = mat1; this.B = mat2;
168 this.loRow = firstRow; this.hiRow = lastRow;
169 this.loCol = firstCol; this.hiCol = lastCol;
170 this.steps = steps;
171 }
172
173 public void compute() throws InterruptedException {
174
175 int rows = hiRow - loRow + 1;
176 int cols = hiCol - loCol + 1;
177 int rblocks = rows / granularity;
178 int cblocks = cols / granularity;
179
180 int n = rblocks * cblocks;
181
182 System.out.println("Using " + n + " segments (threads)");
183
184 Segment[] segs = new Segment[n];
185 Thread [] threads = new Thread [n];
186 CyclicBarrier barrier = new CyclicBarrier(n);
187
188 int k = 0;
189 for (int i = 0; i < rblocks; ++i) {
190 int lr = loRow + i * granularity;
191 int hr = lr + granularity;
192 if (i == rblocks-1) hr = hiRow;
193
194 for (int j = 0; j < cblocks; ++j) {
195 int lc = loCol + j * granularity;
196 int hc = lc + granularity;
197 if (j == cblocks-1) hc = hiCol;
198
199 segs[k] = new Segment(A, B, lr, hr, lc, hc, steps, barrier, segs);
200 threads[k] = new Thread (segs[k]);
201 ++k;
202 }
203 }
204
205 for (k = 0; k < n; ++k) threads[k].start();
206
207 for (k = 0; k < n; ++k) threads[k].join();
208
209 double maxd = 0;
210 for (k = 0; k < n; ++k) {
211 double md = segs[k].maxDiff;
212 if (md > maxd) maxd = md;
213 }
214
215 System.out.println("Max diff after " + steps + " steps = " + maxd);
216
217
218 }
219 }
220
221
222 }
223 |
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