1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain, as explained at |
4 |
* http://creativecommons.org/licenses/publicdomain |
5 |
*/ |
6 |
|
7 |
//import jsr166y.*; |
8 |
import java.util.*; |
9 |
import java.util.concurrent.*; |
10 |
import java.util.concurrent.atomic.*; |
11 |
|
12 |
/** |
13 |
* This is reworked version of one of the tests reported on in the |
14 |
* paper: Guojing Cong, Sreedhar Kodali, Sriram Krishnamoorty, Doug |
15 |
* Lea, Vijay Saraswat and Tong Wen, "Solving irregular graph problems |
16 |
* using adaptive work-stealing", ICPP, 2008. |
17 |
* |
18 |
* It runs the main batching algorithm discussed there for spanning |
19 |
* trees, for a simple regular torus graph, where each node is |
20 |
* connected to its left. right, up, and down neighbors. |
21 |
*/ |
22 |
public class TorusSpanningTree { |
23 |
static final int NCPUS = Runtime.getRuntime().availableProcessors(); |
24 |
|
25 |
// Dimensions for test runs. |
26 |
// graphs have side*side nodes, each with 4 neighbors |
27 |
static final int MIN_SIDE = 1000; |
28 |
static final int MAX_SIDE = 3000; |
29 |
static final int SIDE_STEP = 500; |
30 |
|
31 |
public static void main(String[] args) throws Exception { |
32 |
Random rng = new Random(); |
33 |
int procs = NCPUS; |
34 |
try { |
35 |
if (args.length > 0) |
36 |
procs = Integer.parseInt(args[0]); |
37 |
} |
38 |
catch (Exception e) { |
39 |
System.out.println("Usage: java TorusSpanningTree <threads>"); |
40 |
return; |
41 |
} |
42 |
System.out.println("Number of threads: " + procs); |
43 |
System.out.println("Printing nanosec per edge across replications"); |
44 |
System.out.print("for Toruses with side lengths"); |
45 |
System.out.printf(" from %5d to %5d step %5d\n", |
46 |
MIN_SIDE, MAX_SIDE, SIDE_STEP); |
47 |
ForkJoinPool pool = new ForkJoinPool(procs); |
48 |
|
49 |
for (int side = MIN_SIDE; side <= MAX_SIDE; side += SIDE_STEP) { |
50 |
int n = side * side; |
51 |
Node[] graph = makeGraph(side); |
52 |
System.out.printf( "N:%9d", n); |
53 |
for (int j = 0; j < 8; ++j) { |
54 |
Node root = graph[rng.nextInt(n)]; |
55 |
long start = System.nanoTime(); |
56 |
pool.invoke(new Driver(root)); |
57 |
long elapsed = System.nanoTime() - start; |
58 |
double nanosPerEdge = (double)elapsed / (4 * n); |
59 |
System.out.printf(" %7.2f", nanosPerEdge); |
60 |
if (j == 0) |
61 |
checkSpanningTree(graph, root); |
62 |
resetAll(graph); |
63 |
} |
64 |
System.out.println(); |
65 |
} |
66 |
pool.shutdown(); |
67 |
} |
68 |
|
69 |
static final class Node extends ForkJoinTask<Void> { |
70 |
final Node[] neighbors; |
71 |
Node parent; |
72 |
Node next; |
73 |
volatile int mark; |
74 |
|
75 |
Node(Node[] nbrs) { |
76 |
neighbors = nbrs; |
77 |
parent = this; |
78 |
} |
79 |
|
80 |
static final AtomicIntegerFieldUpdater<Node> markUpdater = |
81 |
AtomicIntegerFieldUpdater.newUpdater(Node.class, "mark"); |
82 |
|
83 |
boolean tryMark() { |
84 |
return mark == 0 && markUpdater.compareAndSet(this, 0, 1); |
85 |
} |
86 |
void setMark() { mark = 1; } |
87 |
|
88 |
/* |
89 |
* Traverse the list ("oldList") embedded across .next fields, |
90 |
* starting at this node, placing newly discovered neighboring |
91 |
* nodes in newList. If the oldList becomes exhausted, swap in |
92 |
* newList and continue. Otherwise, whenever the length of |
93 |
* newList exceeds current number of tasks in work-stealing |
94 |
* queue, push list onto queue. |
95 |
*/ |
96 |
|
97 |
static final int LOG_MAX_BATCH_SIZE = 7; |
98 |
|
99 |
/** |
100 |
* Since tasks are never joined, we bypass Recursive{Action,Task} |
101 |
* and just directly implement exec |
102 |
*/ |
103 |
public boolean exec() { |
104 |
int batchSize = 0; // computed lazily |
105 |
Node newList = null; |
106 |
int newLength = 0; |
107 |
Node oldList = this; |
108 |
Node par = parent; |
109 |
do { |
110 |
Node v = oldList; |
111 |
Node[] edges = v.neighbors; |
112 |
oldList = v.next; |
113 |
int nedges = edges.length; |
114 |
for (int k = 0; k < nedges; ++k) { |
115 |
Node e = edges[k]; |
116 |
if (e != null && e.tryMark()) { |
117 |
e.parent = par; |
118 |
e.next = newList; |
119 |
newList = e; |
120 |
if (batchSize == 0) { |
121 |
int s = getQueuedTaskCount(); |
122 |
batchSize = ((s >= LOG_MAX_BATCH_SIZE)? |
123 |
(1 << LOG_MAX_BATCH_SIZE) : |
124 |
(1 << s)); |
125 |
} |
126 |
if (++newLength >= batchSize) { |
127 |
newLength = 0; |
128 |
batchSize = 0; |
129 |
if (oldList == null) |
130 |
oldList = newList; |
131 |
else |
132 |
newList.fork(); |
133 |
newList = null; |
134 |
} |
135 |
} |
136 |
} |
137 |
if (oldList == null) { |
138 |
oldList = newList; |
139 |
newList = null; |
140 |
newLength = 0; |
141 |
} |
142 |
} while (oldList != null); |
143 |
return false; |
144 |
} |
145 |
|
146 |
// required abstract implementations for ForkJoinTask |
147 |
public final Void getRawResult() { return null; } |
148 |
protected final void setRawResult(Void mustBeNull) { } |
149 |
|
150 |
public void reset() { |
151 |
reinitialize(); |
152 |
parent = this; |
153 |
next = null; |
154 |
mark = 0; |
155 |
} |
156 |
|
157 |
} |
158 |
|
159 |
static final class Driver extends RecursiveAction { |
160 |
final Node root; |
161 |
Driver(Node root) { |
162 |
this.root = root; |
163 |
} |
164 |
public void compute() { |
165 |
root.setMark(); |
166 |
root.fork(); |
167 |
helpQuiesce(); |
168 |
} |
169 |
} |
170 |
|
171 |
static Node[] makeGraph(int sideLength) { |
172 |
int n = sideLength * sideLength; |
173 |
Node[] vs = new Node[n]; |
174 |
for (int i = 0; i < n; ++i) |
175 |
vs[i] = new Node(new Node[4]); |
176 |
|
177 |
// connect each node to left, right, up, down neighbors |
178 |
int maxcol = n - sideLength; |
179 |
int col = 0; |
180 |
for(int i = 0; i < sideLength; ++i) { |
181 |
for(int j = 0; j < sideLength; ++j) { |
182 |
Node[] a = vs[col + j].neighbors; |
183 |
a[0] = vs[col + ((j < sideLength-1)? (j+1) : 0)]; |
184 |
a[1] = vs[col + ((j != 0)? (j-1) : (sideLength-1))]; |
185 |
a[2] = vs[j + ((i < sideLength-1)? (col + sideLength) : 0)]; |
186 |
a[3] = vs[j + ((i != 0)? (col - sideLength) : maxcol)]; |
187 |
} |
188 |
col += sideLength; |
189 |
} |
190 |
return vs; |
191 |
} |
192 |
|
193 |
static void resetAll(Node[] g) { |
194 |
for (int i = 0; i < g.length; ++i) |
195 |
g[i].reset(); |
196 |
} |
197 |
|
198 |
// check that all nodes have parents, and no cycles |
199 |
static void checkSpanningTree(Node[] g, Node root) { |
200 |
int n = g.length; |
201 |
for (int i = 0; i < n; ++i) { |
202 |
Node v = g[i]; |
203 |
Node p = v; |
204 |
int k = n; |
205 |
while (p != root) { |
206 |
if (p == null) |
207 |
throw new RuntimeException("null parent"); |
208 |
if (--k <= 0) |
209 |
throw new RuntimeException("cycle"); |
210 |
p = p.parent; |
211 |
} |
212 |
v.parent = root; |
213 |
} |
214 |
} |
215 |
|
216 |
} |