Java多线程加入问题

Question

因此，我需要使用线程（已经拆分）处理几个数据文件，并且在如何停止主线程直到所有子线程完成之前，我遇到了问题。我环顾四周并尝试使用join（），但这会导致问题：

• 如果我将主线程与最后一个线程一起加入，则由于其他线程同时运行，所以最后一个线程并不总是最后一个要完成的线程
• 如果我将主线程与所有其他线程一起加入，则它们不会同时运行，第二个需要第一个先完成。还尝试了wait（）和notify（），但还有更多问题。这是我的代码的一部分

        public class Matrix extends MapReduce {
        ArrayList<String> VecteurLines = new ArrayList<String>();
        protected int[] nbrLnCol = {0,0};
        protected static double[] res;

        public Matrix(String n) {
            super(n);
        }
        public Matrix(String n,String m){
            super(n,m);
        }
    public void Reduce() throws IOException, InterruptedException, MatrixException {

            for (int i = 1; i <= Chunks; i++) {

                Thread t=new Thread(new RunThread(VecteurLines,i,this));
                t.start();

            }
        }

这是处理线程的类

    public class RunThread extends Matrix implements Runnable {
            Matrix ma;
            ArrayList<String> vec;
            int threadNbr;


            public RunThread(ArrayList<String> vec, int threadNbr,Matrix ma)  {
                super("","");
                this.vec=vec;this.threadNbr=threadNbr;this.ma=ma; }

            @Override
            public void run() {

                FileInputStream fin = null;
                try {
                    fin = new FileInputStream(ma.getNom()+threadNbr+".txt");
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
                Scanner sc = new Scanner(fin);


                while (sc.hasNext()) {
                    String nextString = sc.next();

                    ma.nbrLnCol[0]++;
                    String [] arr = nextString.split(",");
                    ma.nbrLnCol[1]=arr.length;
                    double c=0;
                    for(int j=0;j<arr.length;j++)
                    {
                        c+=(Double.parseDouble(arr[j])*Double.parseDouble(vec.get(j)));

                    }

                    res[threadNbr-1]=c;
                }
                sc.close();
                try {
                    fin.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

                File file = new File(ma.getNom()+threadNbr+".txt");
                file.delete();
            }

Answer 1

尝试这样：

 private List<Thread> threadList = new ArrayList<>();

 public void Reduce() {
     threadList.clear();
     for (int i = 1; i <= Chunks; i++) {
         Thread t  =new Thread(new RunThread(VecteurLines,i,this));
         threadList.add(t);
     }

     // start all worker threads
     for(int i=0; i<threadList.size(); i++){
         threadList.get(i).start();
     }

     // wait until all worker threads is finished
     while (true) {
         int threadIsNotLive = 0;
         for (int i = 0; i < threadList.size(); i++) {
             Thread t = threadList.get(i);
             if (!t.isAlive() || t == null) {
                 ++threadIsNotLive;
             }
         }
         if(threadIsNotLive>0 && (threadList.size() == threadIsNotLive)){
             break;
             // all worker threads is finished
         }
         else {
             Thread.sleep(50);
             // wait until all worker threads is finished
         }
     }
 }

OR

 public void Reduce() {
     List<Thread> threadList = new ArrayList<>();
     for (int i = 1; i <= Chunks; i++) {
         Thread t  =new Thread(new RunThread(VecteurLines,i,this));
         threadList.add(t);
     }

     // start all worker threads
     for(int i=0; i<threadList.size(); i++){
         threadList.get(i).start();
         threadList.get(i).join();
     }
 }