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;
		int step;
		int offset;
		long num;
		long currentPrime;
		long biggestPossible;
		Sieve sieve;
		boolean ready = false;
		boolean done = false;

		// Offset should start at 0
		synchronized public void start(FactorMonitor monitor, int step, int offset) {
			this.monitor = monitor;
			this.step = step;
			this.offset = offset;
			this.num = monitor.currentNum;
			this.biggestPossible = (long)Math.sqrt(num);
			this.sieve = monitor.sieve;
			notify();

			this.ready = true;
			this.done = false;

			findFirstPrime();
		}

		void findFirstPrime() {
			currentPrime = 3;
			for (int i = 0; i < offset; ++i) {
				currentPrime += 2;
				while (!monitor.isPrime(currentPrime))
					currentPrime += 2;
			}
		}

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

		void nextPrime() {
			if (currentPrime > biggestPossible)
				return;

			for (int i = 0; i < step; ++i) {
				currentPrime += 2;
				while (!monitor.isPrime(currentPrime) && currentPrime <= biggestPossible)
					currentPrime += 2;

				if (currentPrime > biggestPossible) {
					this.ready = false;
					monitor.foundBiggest();
					return;
				}
			}
		}

		void findFactor() {
			boolean found = false;
			while (!found && this.ready) {
				if ((num % currentPrime) == 0) {
					found = true;
					if (!monitor.addFactor(currentPrime, num)) {
						this.num = monitor.currentNum;
						findFirstPrime();
						return;
					}
				}

				nextPrime();
			}
		}

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

			while (!done) {
				while (!monitor.isDone() && this.ready) {
					findFactor();
				}

				ready = false;

				while (!ready && !done)
					try { wait(); } catch (InterruptedException ex) {}
			}
		}
	}

	class FactorMonitor {
		Sieve sieve;
		long original;
		long currentNum;
		int biggestLeft;

		boolean done = false;
		ArrayList<Long> arr = new ArrayList<>();

		FactorMonitor(Sieve sieve, long num, int nThreads) {
			this.sieve = sieve;
			this.original = num;
			this.currentNum = num;
			this.biggestLeft = nThreads;

			// We don't want to have to deal with the fact that 2 is a prime
			if (num % 2 == 0)
				addFactor(2, num);
		}

		synchronized boolean addFactor(long factor, long num) {
			// If the thread is working with a stale num,
			// just discard it and tell the thread to restart.
			if (num != currentNum)
				return false;

			while ((currentNum % factor) == 0) {
				currentNum /= factor;
				Long i = new Long(factor);
				arr.add(i);
			}
			notify();

			return true;
		}

		synchronized void foundBiggest() {
			this.biggestLeft -= 1;
			if (biggestLeft == 0) {
				done = true;
				notify();
			}
		}

		boolean isPrime(long num) {
			if (num > sieve.maxNum)
				return false;
			else
				return sieve.isPrime((int)num);
		}

		synchronized boolean isDone() {
			if (done) {
				return true;
			} else if (isPrime(currentNum)) {
				done = true;
				if (currentNum != 1)
					arr.add(new Long(currentNum));
				notify();
				return true;
			} else {
				return false;
			}
		}

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

			Long curr = new Long(currentNum);
			if (currentNum > (long)Math.sqrt(original) && !arr.contains(curr))
				arr.add(curr);

			long[] a = new long[arr.size()];
			for (int i = 0; i < a.length; ++i) {
				a[i] = arr.get(i);
			}
			return a;
		}
	}

	FactorWorker[] factorWorkers = null;
	Thread[] factorThreadPool = null;

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

		if (num <= sieve.maxNum && sieve.isPrime((int)num))
			return new long[] { num };

		// Initiate thread pool
		if (factorThreadPool == null) {
			factorThreadPool = new Thread[nThreads];
			factorWorkers = new FactorWorker[nThreads];
			for (int i = 0; i < nThreads; ++i) {
				FactorWorker w = new FactorWorker();
				factorWorkers[i] = w;
				factorThreadPool[i] = new Thread(w);
				factorThreadPool[i].start();
			}
		}

		FactorMonitor monitor = new FactorMonitor(sieve, num, nThreads);

		// Start workers
		for (int i = 0; i < nThreads; ++i) {
			FactorWorker w = factorWorkers[i];
			w.start(monitor, nThreads, i);
		}

		long[] arr = monitor.getFactors();
		Arrays.sort(arr);
		return arr;
	}

	public void stopThreads() {
		if (factorWorkers == null)
			return;

		for (FactorWorker w: factorWorkers) {
			w.stop();
		}
	}
}