我正在尝试使用多线程实现 Mergesort 的一个版本。首先，我知道这里有十亿个线程（给予或接受......），我读过一些无济于事！我试图证明并行使用线程可以加快进程。然而，我遇到的问题是我的代码没有显示和加速，事实上，恰恰相反。
用一根线，我的时间是几十万。用两个，我的时间增加到几十万，然后用 4 个线程，我的时间接近 7 个数字。我最初的想法是使用 join() 方法并确保它在正确的位置，并且已经这样做了，但没有成功。
任何帮助将不胜感激，示例命令行参数类似于；
java工作16 4（4个线程）。
对整个过程中缺乏评论表示歉意！
import java.util.*;
class working
{
private static int sizeVector;
private static int noThreads;
static void sort(int[] input)
{
mergeSort(input, 0, input.length - 1, noThreads);
}
static void mergeSort(int[] array, int low, int high, int noThreadsUp)
{
//private int noThreadsUp;
if (low < high)
{
int mid = (low+high)/2;
if (noThreadsUp > 1)
{
NewThread td = new NewThread(array, low, mid, noThreadsUp/2);
td.start();
/*try{
td.join();
}catch(Exception e){}*/
mergeSort(array, mid+1, high, noThreadsUp/2);
try{
td.join();//UNSURE WHERE THIS SHOULD BE
}catch(Exception e){}
merge(array, low, mid, high);
}
else
{
mergeSort(array, low, mid, noThreadsUp/2);
mergeSort(array, mid+1, high, noThreadsUp/2);
merge(array, low, mid, high);
}
}
}
static void merge(int[] array, int low, int mid, int high)
{
int[] temp = new int[high - low + 1];
int left = low;
int right = mid+1;
int k = 0;
while (left <= mid && right <= high)
{
if(array[left] < array[right])
{
temp[k] = array[left];
left = left+1;
}
else
{
temp[k] = array[right];
right = right + 1;
}
k = k + 1;
}
if (left <= mid)
{
while(left <= mid)
{
temp[k] = array[left];
left = left + 1;
k = k + 1;
}
}
else if (right <= high)
{
while(right <= high)
{
temp[k] = array[right];
right = right + 1;
k = k + 1;
}
}
for (int m = 0; m < temp.length; m++)
{
array[low+m] = temp[m];
}
}
static int[] readInputArray()
{
int[] a = new int[sizeVector];
for (int i = 0; i < sizeVector; i++)
{
Random generator = new Random();
a[i] = generator.nextInt();
}
return a;
}
static void printArray(int[] array)
{
for(int i = 0; i<array.length; i++)
System.out.println(array[i]);
}
public static void main(String[] args)
{
sizeVector = Integer.parseInt(args[0]);
noThreads = Integer.parseInt(args[1]);
int[] inputArray = readInputArray();
System.out.println("INPUT ARRAY: ");
printArray(inputArray);
long startTime = System.nanoTime();
sort(inputArray);
long endTime = System.nanoTime();
long finalTime = endTime - startTime;
System.out.println("SORTED ARRAY: ");
printArray(inputArray);
System.out.println("Time: " + finalTime);
}
static class NewThread extends Thread
{
private int low;
private int mid;
private int[] array;
private int noThreadsDown;
//private int threads;
public NewThread(int[] array, int low, int mid, int noThreadsDown)
{
this.low = low;//Ensure using the right start
this.mid = mid;//Ensure using the right end
this.array = array;
this.noThreadsDown = noThreadsDown;
//this.threads = threads;
}
public void run()
{
mergeSort(array, low, mid, noThreadsDown/2);
System.out.println(noThreadsDown);
}
}//End NewThread
}