use sectors

projekt/Solver.java

@@ -20,6 +20,7 @@ import javax.swing.JScrollPane;
 
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
 
 final public class Solver extends JPanel  {
 	
@@ -37,6 +38,10 @@ final public class Solver extends JPanel  {
 	// For each cell in the labyrinth: Has solve() visited it yet?
 	private boolean[][] visited; // initialized in solve()
 	private AtomicBoolean[][] visitedAtomic;
+	private AtomicInteger numTasks = new AtomicInteger(0);
+
+	private Semaphore[] sectors;
+	private static final int SECTOR_SIZE = (int) Math.sqrt(DEFAULT_WIDTH_IN_CELLS * DEFAULT_HEIGHT_IN_CELLS) / 50;
 
 	// determined by trial and error
 	private static final int DISTANCE_PER_TASK = DEFAULT_WIDTH_IN_CELLS * DEFAULT_HEIGHT_IN_CELLS / 128;
@@ -123,15 +128,32 @@ final public class Solver extends JPanel  {
 		return pathSoFar.toArray(new Point[0]); 
 	}
 
+	private int getSectorsX() {
+		return (int)Math.ceil((double)labyrinth.getWidth() / SECTOR_SIZE);
+	}
+	private int getSectorsY() {
+		return (int)Math.ceil((double)labyrinth.getHeight() / SECTOR_SIZE);
+	}
+	private int getSectorId(Point p) {
+		return (p.getX() / SECTOR_SIZE) + (p.getY() / SECTOR_SIZE) * getSectorsX();
+	}
+
 	public Point[] solveConcurrently() {
 		// dummy origin direction for start
 		PointAndDirection start = new PointAndDirection(labyrinth.getStart(), null);
 
-		visitedAtomic = new AtomicBoolean[labyrinth.getWidth()][labyrinth.getHeight()];
-		for (int i = 0; i < visitedAtomic.length; i++) {
-			for (int j = 0; j < visitedAtomic[i].length; j++) {
-				visitedAtomic[i][j] = new AtomicBoolean(false);
-			}
+		// visitedAtomic = new AtomicBoolean[labyrinth.getWidth()][labyrinth.getHeight()];
+		// for (int i = 0; i < visitedAtomic.length; i++) {
+		// 	for (int j = 0; j < visitedAtomic[i].length; j++) {
+		// 		visitedAtomic[i][j] = new AtomicBoolean(false);
+		// 	}
+		// }
+
+		visited = new boolean[labyrinth.getWidth()][labyrinth.getHeight()];
+
+		sectors = new Semaphore[getSectorsX() * getSectorsY()];
+		for (int i = 0; i < sectors.length; i++) {
+			sectors[i] = new Semaphore(1);
 		}
 
 		ForkJoinPool pool = ForkJoinPool.commonPool();
@@ -140,6 +162,9 @@ final public class Solver extends JPanel  {
 		ConcurrentSolverTask t = new ConcurrentSolverTask(start, pathSoFar, pool);
 		Point[] result = pool.invoke(t);
 
+		System.out.println("Used tasks: " + numTasks.get());
+		System.out.println("Task to Solution Length Ratio: " + (double)result.length / numTasks.get());
+
 		return result;
 	}
 
@@ -149,6 +174,7 @@ final public class Solver extends JPanel  {
 		private ArrayDeque<Point> pathSoFar;
 		private ForkJoinPool pool;
 		private ArrayList<ConcurrentSolverTask> subtasks;
+		private int currentSector;
 		public ConcurrentSolverTask(PointAndDirection start, ArrayDeque<Point> pathSoFar, ForkJoinPool pool) {
 			this.start = start;
 			this.pathSoFar = pathSoFar;
@@ -156,9 +182,33 @@ final public class Solver extends JPanel  {
 
 			this.backtrackStack = new ArrayDeque<>();
 			this.subtasks = new ArrayList<>();
+			this.currentSector = -1;
+		}
+
+		private void acquireSector(Point p) {
+			if (getSectorId(p) == this.currentSector) return;
+			if (this.currentSector >= 0) {
+				// release previous sector
+				sectors[this.currentSector].release();
+			}
+			this.currentSector = getSectorId(p);
+			try {
+				// acquire new sector
+				sectors[this.currentSector].acquire();
+			} catch (InterruptedException e) {
+				System.out.println(e);
+				return;
+			}
+		}
+
+		private void releaseSector() {
+			if (this.currentSector >= 0) {
+				sectors[this.currentSector].release();
+			}
 		}
 
 		public Point[] compute() {
+			numTasks.incrementAndGet();
 			int currentLength = 0;
 			Point current = this.start.getPoint();
 
@@ -197,11 +247,19 @@ final public class Solver extends JPanel  {
 
 					// check if that cell has been visited
 					// set visitedAtomic to true if it has not been visited
-					if (!visitedAtomic[neighbour.x][neighbour.y].compareAndSet(false, true)) {
-						continue;
-					}
+					// if (!visitedAtomic[neighbour.x][neighbour.y].compareAndSet(false, true)) {
+					// 	continue;
+					// }
+
+					acquireSector(neighbour);
+					if (visited[neighbour.x][neighbour.y]) continue;
+					visited[neighbour.x][neighbour.y] = true;
+					releaseSector();
+					
+
 					// System.out.println("Found unvisited neighbour: " + neighbour);
 					if (currentLength >= DISTANCE_PER_TASK) {
+						releaseSector();
 						// if we have reached the distance limit, create a subtask
 						ArrayDeque<Point> subPath = this.pathSoFar.clone();
 						subPath.addLast(current);
@@ -210,8 +268,9 @@ final public class Solver extends JPanel  {
 							subPath,
 							this.pool
 						);
-						subtask.fork();
 						subtasks.add(subtask);
+
+						subtask.fork();
 					} else {
 						if (next == null) {
 							// visit first unvisited neighbour next
@@ -224,7 +283,6 @@ final public class Solver extends JPanel  {
 						}
 					}
 				}
-
 				// at least one unvisited neighbour found
 				if (next != null) {
 					pathSoFar.addLast(current);
@@ -232,6 +290,7 @@ final public class Solver extends JPanel  {
 					currentLength++;
 				}
 				if (next == null) {
+					releaseSector();
 					// no unvisited neighbour found
 					// backtrack if possible
 					if (this.backtrackStack.isEmpty()) {