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PageRank.java
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PageRank.java
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import java.util.ArrayList;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CyclicBarrier;
public class PageRank {
private int num;
private int[] source;
private int[] dest;
// Cyclic barrier for synchronizing threads with the current superstep.
public CyclicBarrier barrier;
public ArrayList<Integer> superStep = new ArrayList<Integer>();
// Result map to store the final vertex values
private ConcurrentHashMap<Integer, Double> res = new ConcurrentHashMap<Integer, Double>();
// Map to find if a thread has halted
private ConcurrentHashMap<Integer, Integer> halt = new ConcurrentHashMap<Integer, Integer>();
// Map to store the messages passed between threads mapped to their vertex ID
private ConcurrentHashMap<Integer, ArrayList<ArrayList<Double>>> incoming = new ConcurrentHashMap<Integer, ArrayList<ArrayList<Double>>>();
public PageRank(int size, int[] fromVertices, int[] toVertices) {
num = size;
source = fromVertices;
dest = toVertices;
superStep.add(1);
for (int i = 0; i < num; i++) {
ArrayList<ArrayList<Double>> t = new ArrayList<ArrayList<Double>>();
ArrayList<Double> q = new ArrayList<Double>();
t.add(q);
incoming.put(i, t);
}
barrier = new CyclicBarrier(num, new Runnable() {
public void run() {
superStep.set(0, superStep.get(0) + 1);
}
});
}
public void run() throws InterruptedException {
for (int i = 0; i < num; i++) {
new Thread(new Runnable() {
private int tid;
private int tnum;
private int[] tsource;
private int[] tdest;
private CyclicBarrier br;
private ArrayList<Integer> step = new ArrayList<Integer>();
private ConcurrentHashMap<Integer, ArrayList<ArrayList<Double>>> tincoming = new ConcurrentHashMap<Integer, ArrayList<ArrayList<Double>>>();
private ConcurrentHashMap<Integer, Double> result = new ConcurrentHashMap<Integer, Double>();
@Override
public void run() {
PageRankVertex p = new PageRankVertex(tid, tnum, tincoming);
// Run the loop till all vertices have halted
while (halt.size() < tnum) {
int tempStep;
synchronized (this) {
// Get the current superstep
tempStep = step.get(0);
}
if (tempStep > 1) {
// If a vertex has not halted, then compute the new value from messages from the
// last superstep.
if (p.getHalt() == 0) {
ArrayList<Double> message = new ArrayList();
ArrayList<ArrayList<Double>> mTemp = new ArrayList<ArrayList<Double>>();
mTemp = tincoming.get(tid);
try {
for (int k = 0; k < mTemp.size(); k++) {
if (mTemp.get(k).size() > 0) {
// Only the messages from the last superstep have to be used for value
// calculation
if (mTemp.get(k).get(0) == (double) (tempStep - 1)) {
message.add(mTemp.get(k).get(1));
}
}
}
} catch (Exception e) {
}
synchronized (this) {
// Send the received messages for calculation
p.compute(message);
// Check if vertex is supposed to halt
p.voteToHalt();
}
}
// If vertex has halted, then add the ID to halt map
else if (!halt.containsKey(tid)) {
halt.put(tid, 1);
}
}
int check = 0;
int outNum = 0;
// Check if the vertex has outgoing edges
for (int j = 0; j < tsource.length; j++) {
if (tsource[j] == tid) {
outNum++;
check = 1;
}
}
// If the vertex is disconnected, then send to all vertices
if (check == 0) {
for (int l = 0; l < num; l++) {
synchronized (this) {
p.sendMessageTo(l, (double) (p.getValue() / tnum), (double) tempStep);
}
}
}
// Send messages to all outgoing edges
else {
for (int j = 0; j < tsource.length; j++) {
if (tsource[j] == tid) {
synchronized (this) {
p.sendMessageTo(tdest[j], (double) (p.getValue() / outNum), (double) tempStep);
}
}
}
}
try {
// Wait for other threads to complete the superstep
br.await();
} catch (InterruptedException e) {
} catch (BrokenBarrierException e) {
}
}
// Store the final value in the map
result.put(tid, p.getValue());
if (result.size() == tnum) {
for (int l = 0; l < tnum; l++) {
System.out.println(result.get(l));
}
}
br.reset();
return;
}
public Runnable init(int pid, int pnum, int[] psource, int[] pdest,
ConcurrentHashMap<Integer, Double> res,
ConcurrentHashMap<Integer, ArrayList<ArrayList<Double>>> m, ArrayList<Integer> st,
CyclicBarrier barrier) {
tid = pid;
tnum = pnum;
tsource = psource;
tdest = pdest;
tincoming = m;
step = st;
br = barrier;
result = res;
return this;
}
}.init(i, num, source, dest, res, incoming, superStep, barrier)).start();
}
}
public static void main(String[] args) {
// Graph has vertices from 0 to `size-1`
// and edges 1->0, 2->0, 3->0
int size = 5;
int[] from = {1,2,3 };
int[] to = { 0, 0, 0 };
PageRank pr = new PageRank(size, from, to);
try {
pr.run();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}