當我添加更多的線程處理時間增加？

我正在做一個並行的圖像處理程序，我有4個內核，所以當我在少於5個的線程上運行程序時，應該比僅在1個線程上運行時有所改進，我想那裏沒有任何改進，因爲圖片可能太小，所以由於線程而導致開銷。所以我用8142x2175圖片仍然沒有任何改進。問題來自Eclipse嗎？當我添加更多的線程處理時間增加？

這是我的主要圖像處理程序，我包括類之一，你可以看到我使用Java和Eclipse的運行它。

public class Main { 
    public static void main(String[] args) throws IOException { 

     final File imageFile= new File ("C:\\Users\\user\\Desktop\\Parallel\\pic8142x2175.jpg"); 
     BufferedImage orgImg= ImageIO.read(imageFile); 

     // the destination buffered image 
     BufferedImage destImg = new BufferedImage(orgImg.getWidth(), orgImg.getHeight(), 
         BufferedImage.TYPE_INT_RGB); 

     // let the user enter number of thread 
     System.out.println(" please enter number of threads"); 
     Scanner in = new Scanner(System.in); 
     int nThreads=in.nextInt(); 

     // create the threads 
     ExecutorService executor = Executors.newFixedThreadPool(nThreads); 

     // assign each thread with its own runnable 
     for (int i=0; i<nThreads;i++){ 

      //Runnable gsr = new GreyscaleRunnable(orgImg, i, nThreads,destImg); 
      //Runnable pr = new PixelateRunnable(orgImg,20,i,nThreads,destImg); 
      Runnable fr= new FlipRunnable(orgImg,i,nThreads,destImg); 
       executor.execute(fr); 

      }// end of for loop 

     // This will make the executor accept no new threads 
     // and finish all existing threads in the queue 
     executor.shutdown(); 
     // Wait until all threads are finish 


    } 

}

FlipRunnable類

public class FlipRunnable implements Runnable{ 

    private BufferedImage img; 
    private BufferedImage dest; 
    private int my_rank, thread_count; 

    // constructor of the class 
     public FlipRunnable(BufferedImage img,int my_rank,int thread_count,BufferedImage dest) { 
      this.img=img; 
      this.my_rank=my_rank; 
      this.thread_count=thread_count; 
      this.dest=dest; 
     } 

     long startTime = System.currentTimeMillis(); 

    @Override 
    public void run() { 

     int localRows = img.getHeight()/thread_count; 
     int myFirstRow = my_rank * localRows; 
     int myLastRow = (my_rank + 1) * localRows - 1; 

     for (int i = myFirstRow; i <= myLastRow; i++) { 
      for (int j = 0; j < img.getWidth(); j++){ 

       int px = img.getRGB(j, i); 

       dest.setRGB(img.getWidth() - j - 1, i, px); 


      }// end of j loop 

     }// end of i loop 

     String dstName = "C:\\Users\\user\\Desktop\\Parallel\\funFlipped.jpg"; 
     File dstFile = new File(dstName); 
     try { 
      ImageIO.write(dest, "jpg", dstFile); 
     } catch (IOException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 

     System.out.println("Output image: " + dstName); 

     // the total time 
     long endTime = System.currentTimeMillis(); 
     long totalTime = endTime - startTime; 
     System.out.println("time is:"+totalTime); 
    } 

}

來源

2013-12-13 user3099142

首先，每個工人似乎覆蓋目標圖像... –

另外，'setRGB（）''是synchronized'，所以必須有大量爭的工人之間。看起來你更好地將圖像複製到普通數組並在那裏工作。 –

是的，我希望工作人員互相覆蓋，這樣我就可以得到整個圖像，而不僅僅是線程工作的部分。對不起我的英語，我試圖說的是，當我沒有讓工人覆蓋，我的輸出只是圖像的一部分，這樣我就完成了整個圖像 – user3099142