package be.ac.vub.ir.multithreading;

import flanagan.math.Fmath;

public class BarrierWithReduction0 {
	final int NBR_ELEMENTS = 10, NBR_RUNS = 4;
	int[] data = new int[NBR_ELEMENTS];
	
	// ** Main **
	public static void main(String[] args) {
		new BarrierWithReduction0().runSeq();
		System.out.println("PARALLEL RUN:");
		new BarrierWithReduction0().runParallel();
	}
	
	void runSeq(){
		for(int r=0;r<NBR_RUNS;r++){
			for(int i=0;i<NBR_ELEMENTS;i++)
				data[i] = i*r;
			float avg = average(data); // after each run, the average is calculated
			System.out.println("Average at run "+r+": "+Fmath.truncate(avg, 3));
		}
	}
	
	Master master;
	// ** DATA **
	void setElement(int i, int value){ data[i]=value; }
	void print(){
		for(int i=0;i<data.length;i++)
			System.out.print(" "+data[i]);
		System.out.println();
	}
	float average(int[] data){
		long sum = 0;
		for(int i=0;i<data.length;i++)
			sum += data[i];
		return ((float)sum/data.length);
	}
	// ** parallel run **
	void runParallel(){
		master = new Master();
		master.start();
		startThreads();
	}
	void startThreads(){
		for(int i=0;i<NBR_ELEMENTS;i++){
			final int I = i;
			// ** threads **
			Thread t = new Thread(){
				public void run(){
					System.out.println("Thread "+I+" starts.");
					for(int r=0;r<NBR_RUNS;r++){
						setElement(I, I*r);
						waitForMaster(r != NBR_RUNS-1); // last run the threads must not go in a wait
					}
				}
			};
			t.start();
		}
	}
	void sleepAWhile(){
		try {
			Thread.sleep(1000); // to test whether sync works fine
		} catch (InterruptedException e) {
		}
	}
	// ** thread pool synchronization (barrier) **
	int nbrWaiting=0;
	synchronized void waitForMaster(boolean goAsleep){ // here the threads go asleep
		nbrWaiting++;
		if (nbrWaiting == NBR_ELEMENTS){
			System.out.print("Array =");print();
			synchronized(master){
				master.notify();
			}
			System.out.println("CALL MASTER...      ");
		}
		if (goAsleep){
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
	synchronized void wakeUpThreads(){ // must be synchronized!! master must have ownership
		nbrWaiting=0;
		notifyAll();
	}
	
	// ** Master class **
	class Master extends Thread{
		
		@Override
		public void run(){ // 

			sleepAWhile();
			for(int r=0;r<NBR_RUNS;r++){
				System.out.println("master goes asleep");System.out.flush();
				try {
					synchronized(this){
						wait();
					}
				} catch (InterruptedException e) {}
				System.out.print("master wakes up: ");
				
				float avg = average(data);

				System.out.println("Average at run "+r+" = "+Fmath.truncate(avg, 3));
				wakeUpThreads();
			}
		}
	}
}