uni/inf2440/hw2/Parallel.java

import java.util.ArrayList;
import java.util.Arrays;

class Parallel implements Solver {
	class SolverWorker implements Runnable {
		Sieve sieve;
		int step;
		int offset;

		SolverWorker(Sieve mainSieve, int step, int offset) {
			byte[] arr = new byte[mainSieve.arr.length];
			System.arraycopy(mainSieve.arr, 0, arr, 0, arr.length);

			this.sieve = new Sieve(mainSieve.maxNum, arr);
			this.sieve.smallPrimesGenerated = true;

			this.step = step;
			this.offset = offset;
		}

		public void run() {
			sieve.generatePrimes(step, offset);
		}
	}

	public void solve(Sieve sieve) {
		// Generate primes less than sqrt(n)
		sieve.generateSmallPrimes();

		int nThreads = Runtime.getRuntime().availableProcessors();
		nThreads = Math.min(nThreads, 8);

		Thread[] threads = new Thread[nThreads];
		SolverWorker[] workers = new SolverWorker[nThreads];

		// Start threads
		for (int i = 0; i < nThreads; ++i) {
			SolverWorker w = new SolverWorker(sieve, nThreads, (i * 2) + 1);
			workers[i] = w;

			Thread t = new Thread(w);
			threads[i] = t;
			t.start();
		}

		// Wait for threads
		for (Thread t: threads) {
			try { t.join(); } catch (InterruptedException ex) {}
		}

		// Merge
		for (int i = 0; i < sieve.arr.length; ++i) {
			for (SolverWorker w: workers) {
				sieve.arr[i] = (byte)(sieve.arr[i] | w.sieve.arr[i]);
			}
		}
	}

	class FactorWorker implements Runnable {
		FactorMonitor monitor;
		long num;
		int sqrt;
		int[] primes;
		int step;
		int offset;
		boolean running;
		boolean done;

		FactorWorker(FactorMonitor monitor, int step, int offset) {
			this.monitor = monitor;
			this.primes = monitor.primes;
			this.num = monitor.num;
			this.sqrt = (int)Math.sqrt(num);
			this.step = step;
			this.offset = offset;
			this.done = false;
		}

		void go() {
			int start = offset + monitor.sequentialPrimes;
			for (int i = start; monitor.running; i += step) {
				if (primes[i] == 0 || primes[i] > sqrt)
					break;

				if (num % primes[i] == 0) {
					monitor.addFactor(primes[i], num);
					break;
				}
			}

			running = false;
			monitor.workerStopped();
		}

		synchronized void start(long num) {
			this.num = num;
			this.sqrt = (int)Math.sqrt(num);
			running = true;
			notify();
		}

		synchronized void stop() {
			done = true;
			notify();
		}

		synchronized public void run() {
			while (!done) {
				while (!running && !done)
					try { wait(); } catch (InterruptedException ex) {}

				if (!done)
					go();
			}
		}
	}

	class FactorMonitor {
		final int sequentialPrimes = 4;

		Sieve sieve;
		long num;
		int nThreads;

		int[] primes;
		boolean running;
		boolean done;
		boolean foundFactor;

		int workersLeft;

		FactorWorker[] workers;
		Thread[] threads;

		ArrayList<Long> factors = new ArrayList<>();

		FactorMonitor(Sieve sieve, long num, int nThreads) {
			this.primes = sieve.getPrimes();
			this.num = num;
			this.nThreads = nThreads;

			this.done = false;

			// We do the first few primes sequentially, as they're
			// very likely to be factors
			for (int i = 0; i < sequentialPrimes; ++i) {
				while (this.num % primes[i] == 0) {
					factors.add(new Long(primes[i]));
					this.num /= primes[i];
				}
			}

			this.workers = new FactorWorker[nThreads];
			this.threads = new Thread[nThreads];
			for (int i = 0; i < nThreads; ++i) {
				FactorWorker w = new FactorWorker(this, nThreads, i);
				Thread t = new Thread(w);
				this.workers[i] = w;
				this.threads[i] = t;
				t.start();
			}

			go();
		}

		synchronized void addFactor(int prime, long num) {
			foundFactor = true;
			if (num != this.num)
				return;

			do {
				this.num /= prime;
				factors.add(new Long(prime));
			} while (this.num % prime == 0);
			running = false;
		}

		synchronized void workerStopped() {
			workersLeft -= 1;
			if (workersLeft != 0)
				return;

			if (foundFactor) {
				go();
			} else {
				done = true;
				notify();

				for (FactorWorker w: workers)
					w.stop();
			}
		}

		synchronized long[] getFactors() {
			while (!done)
				try { wait(); } catch (InterruptedException ex) {}

			if (num != 1)
				factors.add(new Long(num));

			long[] arr = new long[factors.size()];
			for (int i = 0; i < arr.length; ++i)
				arr[i] = factors.get(i);

			Arrays.sort(arr);
			return arr;
		}

		synchronized void go() {
			running = true;
			foundFactor = false;
			workersLeft = nThreads;
			for (FactorWorker w: workers)
				w.start(num);
		} 
	}

	public long[] factor(Sieve sieve, long num) {
		int nThreads = Runtime.getRuntime().availableProcessors();
		nThreads = Math.min(nThreads, 8);

		FactorMonitor monitor = new FactorMonitor(sieve, num, nThreads);
		return monitor.getFactors();
	}

	public void stopThreads() {
	}
}