Fork-Join Pool沒有產生任何結果，而串行代碼則可以最佳地工作

Question

我編寫的其他串行代碼運行完美，但是此並行版本沒有提供任何輸出，它只會打印問候，我正在用“嘿”測試它，甚至從未到達該行，即卡在invoke方法上，我無法找不到在線有用的資源。

請幫助我了解我要去哪里錯了，我是並行編程的新手。

該代碼是一個中值濾波程序，當給定數組x = [2,80,6,3]時，濾波后的數組y = [2,6,6,3]的計算公式為：

y [1] =中位數[2 2 80] = 2

y [2] =中位數[2 80 6] =中位數[2 6 80] = 6

y [3] =中位數[80 6 3] =中位數[3 6 80] = 6

y [4] =中位數[6 3 3] =中位數[3 3 6] = 3

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.io.PrintWriter;

public class ParallelFilter extends RecursiveAction {

static final int SEQUENTIAL_THRESHOLD=500; 
ArrayList<Float> inputArray;
int sizeOfFilter;
ArrayList<Float> outputlist;
ArrayList<Float> arrayFiltered;

float high;
float low;

public ParallelFilter(ArrayList<Float> inputArray,int sizeOfFilter,float           high,float low)
                 {

  this.inputArray=inputArray;
   this.outputlist=outputlist;
  this.sizeOfFilter=sizeOfFilter;
  this.arrayFiltered=arrayFiltered;
  //this.index=index;
  this.high=high;
  this.low=low;
 }




 protected void compute()
 {
  int index=1;

  if((high - low) < SEQUENTIAL_THRESHOLD )
  {
      while(inputArray.size() > sizeOfFilter){
     for(int i=0; i<sizeOfFilter;i++){

         arrayFiltered.add(i,inputArray.get(i));

     }

         Collections.sort(arrayFiltered);
         float median = arrayFiltered.get(arrayFiltered.size()/2);
         outputlist.add(index,median);
         inputArray.remove(inputArray.get(0));
         arrayFiltered.clear();
         index=index+1;

      }

      outputlist.add(inputArray.get(inputArray.size()-1));
  }


    else{

      ParallelFilter leftTask = new       ParallelFilter(inputArray,sizeOfFilter,low,(low+high)/2);
      ParallelFilter rightTask = new ParallelFilter(inputArray,sizeOfFilter,(low+high)/2,high);
      leftTask.fork();
      rightTask.compute();
      leftTask.join();
  }

  }



   public static void main(String[] args){

  try
  {
      Scanner sc;
      sc = new Scanner(new File("inp1.txt"));
      sc.useDelimiter(" ");
      ArrayList<Float> inputlist = new ArrayList<>();

      //POPULATE LIST FROM FILE
      while (sc.hasNextLine()) {

      if(sc.nextLine().length() == 1){continue;}
      String[] parts = sc.nextLine().split(" "); // split each line by " "

      inputlist.add(Float.parseFloat(parts[1]))  ; 
      // System.out.println(parts[1]);
                           }

      System.out.println("Enter filter size : ");
      Scanner in = new Scanner(System.in);
      int sizeOfFilter = in.nextInt();
      if (sizeOfFilter < 3 || sizeOfFilter / 2 == 0) {
             System.out.println("Filter size should be odd and bigger than 3");
         }

      float low = inputlist.get(0);
      float high = inputlist.get(inputlist.size()-1);

      ParallelFilter pf = new ParallelFilter(inputlist,sizeOfFilter,low,high);
      System.out.println("hello");
      ForkJoinPool forkJoinPool = new ForkJoinPool();
      forkJoinPool.invoke(pf);//suspect the problem is here...

      for (int i=0; i<pf.outputlist.size();i++){

      System.out.println(pf.outputlist.get(i));}
      System.out.println("hey");

    }
  catch(Exception e){}

 }



  }

Answer 1

如果在運行該程序時鍵入“ hey”，則會得到解析異常，由於catch塊為空，該異常被忽略。

同樣在您的構造函數中，您有this.arrayFiltered = arrayFiltered; 實際上沒有任何作用，因為您沒有名稱為arrayFiltered的參數。 它導致arrayFiltered不會被初始化，從而導致arrayFiltered.add(i, inputArray.get(i)); NPE arrayFiltered.add(i, inputArray.get(i));

我建議喲把e.printStackTrace(); 在catch塊中，它將立即顯示所有錯誤。 當然，您需要學習如何使用調試器。

還有這部分

            if (sc.nextLine().length() == 1) {
                continue;
            }
            String[] parts = sc.nextLine().split(" ");

是錯的。 因為您在這里讀了兩行。 您需要讀取一次行，記住結果然后對其進行測試並進行解析。

像這樣

            String line = sc.nextLine();
            if (line.length() == 1) {
                continue;
            }
            String[] parts = line.split(" ");