package geym.conc.ch3.fork;

import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

public class CountTask extends RecursiveTask<Long>{
    private static final int THRESHOLD = 10000;
    private long start;
    private long end;
    
    public CountTask(long start,long end){
        this.start=start;
        this.end=end;
    }
    
    public Long compute(){
        long sum=0;
        boolean canCompute = (end-start)<THRESHOLD;
        if(canCompute){
            for(long i=start;i<=end;i++){
                sum +=i;
            }
        }else{
            //分成100个小任务
            long step=(start+end)/100;
            ArrayList<CountTask> subTasks=new ArrayList<CountTask>();
            long pos=start;
            for(int i=0;i<100;i++){
                long lastOne=pos+step;
                if(lastOne>end)lastOne=end;
                CountTask subTask=new CountTask(pos,lastOne);
                pos+=step+1;
                subTasks.add(subTask);
                subTask.fork();
            }
            for(CountTask  t:subTasks){
                sum+=t.join();
            }
        }
        return sum;
    }
    
    public static void main(String[]args){
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        CountTask task = new CountTask(0,200000000000L);
        ForkJoinTask<Long> result = forkJoinPool.submit(task);
        try{
            long res = result.get();
            System.out.println("sum="+res);
        }catch(InterruptedException e){
            e.printStackTrace();
        }catch(ExecutionException e){
            e.printStackTrace();
        }
    }
}