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Java parallel Bucket Sort

程序员文章站 2022-04-01 16:52:43
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这是桶排序的Java 平行计算版本,随着生成的随机整数的复杂度增加,也就是生成区间的不断扩大,加速比会明显增长。数据样本太简单的话,无法体现平行计算的威力。特此声明:桶排序平行化的基本思路来自于: Professor Ian Bond in Massey University. 初始版本用CPP+MPI 编写,我本人用Java重写了基本算法,而且增加了自己的算法,数据进桶等比例缩小和出桶时的等比例放大. 目前,只开了4个线程,读者可以根据自身情况手动增加线程,但是需要修改代码。你不能用循环动态建立线程,很慢!
这是初始版本,后期需要优化,也就是继续加速,增大加速比. 平行化是否成功的关键就是看加速比:linear time / parallel time

-Xms18024M -Xmx18024M
请注意,推荐内存 32 G,你可以根据自己的内存调整随机整数生成区间,当心JVM heap out of memory.

public class MyTimer {
    private static long begin;

    public static void time_start(){
        begin = System.nanoTime();
    }

    public static double time_end_milli_seconds(){
        return System.nanoTime()-begin/1e6;

    }

    public static double time_end_seconds(){
        double total_time =  (System.nanoTime()-begin)/1e6;
        return ((double)((int)total_time))/1000;

    }

}
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class RandomGenerator {

    public static int[] random_generate(int min,int max,int numtrials){

        int[] int_array = new int[numtrials];

        Random random = new Random();

        for (int i = 0; i < numtrials; i++) {
            int random_num = random.nextInt(max)%(max-min+1) + min;
            int_array[i] = random_num;
        }

        return int_array;
    }

}
import java.util.ArrayList;
import java.util.List;

public class BucketSort {

    public int[] bucket_sort(int[] original_array,int max){

            // index: 0-99 but max is : 100 . the point is the array index for bucketsort
           int[] store_array = new int[max+1];

            for (int i = 0; i < original_array.length; i++) {
                int int_num = original_array[i];

                // here is the miracle of bucketsort
                store_array[int_num]= ++store_array[int_num];
            }

           int[] final_sorted_array = new int[original_array.length];
           int cherry_pointer = 0;

        for (int cherry = 0; cherry < store_array.length; cherry++) {

            int cherry_num = store_array[cherry];
            for (int j = 0; j < cherry_num; j++) {
                final_sorted_array[cherry_pointer]=cherry;
                ++cherry_pointer;
            }

        }

           return final_sorted_array;
    }
}
public class SmallBucketThread extends Thread{

    public int[] original_array;
    public int[] final_sorted_array;
    public int bucket_num;
    public int bucket_size;

    public int shrink_number(int item,int bucket_num,int bucket_size){

        return item-(bucket_num*bucket_size);
    }

    public int recover_number(int item,int bucket_num,int bucket_size){

        return item+(bucket_num*bucket_size);
    }

    public SmallBucketThread(int[] original_array,int bucket_num,int bucket_size) {
        this.original_array = original_array;
        final_sorted_array = new int[original_array.length];
        this.bucket_num = bucket_num;
        this.bucket_size = bucket_size;
    }

    @Override
    public void run() {
        bucket_sort_parallel(original_array,bucket_size);
    }



    public void bucket_sort_parallel(int[] original_array,int max){


        // index: 0-99 but max is : 100 . the point is the array index for bucketsort
        int[] store_array = new int[max+1];

        for (int i = 0; i < original_array.length; i++) {
            // empty item in array is : 0
            if (original_array[i]!=0){
                // 71 -> 21 , 89->14 , save physical memory
                int int_num = shrink_number(original_array[i],bucket_num,bucket_size);
                // here is the miracle of bucketsort
                store_array[int_num]= ++store_array[int_num];
            }

        }


        int cherry_pointer = 0;
        // loop the cherry store....
        for (int cherry = 0; cherry < store_array.length; cherry++) {

            int cherry_num = store_array[cherry];
            for (int j = 0; j < cherry_num; j++) {
                final_sorted_array[cherry_pointer] = recover_number(cherry,bucket_num,bucket_size);
                ++cherry_pointer;
            }

        }


    }
}
import java.util.ArrayList;
import java.util.List;

public class BucketSortParallel {

     public double bucket_sort_parallel(int min_cherry,int max_cherry,int cherry_total_num) throws InterruptedException {


         MyTimer.time_start();

         int bucket_size = cherry_total_num/4;

         int[] random_array = RandomGenerator.random_generate(min_cherry,max_cherry,cherry_total_num);

         // 1.576 secs

        // System.out.println("random generated !"+MyTimer.time_end_seconds()+" s");

       //  MyTimer.time_start();

         int[] arr0 = new int[cherry_total_num]; int pointer0 = 0;
         int[] arr1 = new int[cherry_total_num]; int pointer1 = 0;
         int[] arr2 = new int[cherry_total_num]; int pointer2 = 0;
         int[] arr3 = new int[cherry_total_num]; int pointer3 = 0;

          // 0.433 s

       //  System.out.println("int[] arr generated !"+MyTimer.time_end_seconds()+" s");

       //  MyTimer.time_start();
         // range random number in different areas.... 1-25,26-50,51-75,76-100
         for (int i = 0; i < random_array.length; i++) {

             int bucket_num = random_array[i] / bucket_size;

             switch (bucket_num)
             {
                 case 0: arr0[pointer0] = random_array[i]; ++pointer0;
                     break;

                 case 1: arr1[pointer1] = random_array[i]; ++pointer1;
                     break;

                 case 2: arr2[pointer2] = random_array[i]; ++pointer2;
                     break;

                 case 3: arr3[pointer3] = random_array[i]; ++pointer3;
                     break;
             }

         }  // all cherries are in the right area

       //  System.out.println("cherry buckets are ready !"+MyTimer.time_end_seconds()+" s");
         // 1.401 s

       //  MyTimer.time_start();
         // start parallel

         SmallBucketThread thread0 = new SmallBucketThread(arr0,0,bucket_size);
         SmallBucketThread thread1 = new SmallBucketThread(arr1,1,bucket_size);
         SmallBucketThread thread2 = new SmallBucketThread(arr2,2,bucket_size);
         SmallBucketThread thread3 = new SmallBucketThread(arr3,3,bucket_size);

         thread0.start();
         thread1.start();
         thread2.start();
         thread3.start();

         thread0.join();
         thread1.join();
         thread2.join();
         thread3.join();

         List list = new ArrayList<int[]>();
         list.add(thread0.final_sorted_array);
         list.add(thread1.final_sorted_array);
         list.add(thread2.final_sorted_array);
         list.add(thread3.final_sorted_array);

       //  System.out.println("parallel is done !"+MyTimer.time_end_seconds()+" s");
         // 1.586 s

         double time_end = MyTimer.time_end_seconds();

        // this.print_array(list);

         return time_end;

     }

     public void print_array(List list)
     {
         for (int i = 0; i < list.size(); i++) {

              int[] array = (int[]) list.get(i);

             for (int j = 0; j < array.length; j++) {
                 if (array[j]!=0)
                     System.out.println(array[j]);

             }

         }
     }

     public void print_array(int[] array){
         for (int j = 0; j < array.length; j++) {

                 System.out.print(array[j]+"-");

         }
     }


}
public class TestBucketSort {

    public double linear_bucketsort(int min,int max,int num_trails){

        MyTimer.time_start();

        BucketSort bucketSort = new BucketSort();
        RandomGenerator randomGenerator = new RandomGenerator();

        int[] random_array = randomGenerator.random_generate(min,max,num_trails);

        int[] sorted_array = bucketSort.bucket_sort(random_array,max);

        double time_end = MyTimer.time_end_seconds();

 /*     for (int i = 0; i < sorted_array.length; i++) {
            System.out.println(sorted_array[i]);
        }*/

      //  System.out.println("Time elapse : "+time_end+"s   sorted_array.length: "+sorted_array.length);

        return time_end;
    }

    public static void main(String[] args) throws InterruptedException {

        int min = 1;
        int max = 1999999999; // 1.9 billion
        int num_trails = 100000000; // 100 million

        TestBucketSort testBucketSort = new TestBucketSort();
        double linear_time =  testBucketSort.linear_bucketsort(min,max,num_trails);

        BucketSortParallel parallel = new BucketSortParallel();
        double parallel_time = parallel.bucket_sort_parallel(min,max,num_trails);

       System.out.println("linear_time: "+linear_time+" secs");
       System.out.println("parallel_time: "+parallel_time+" secs");
       System.out.println("speed up : "+ (linear_time/parallel_time));


    }
}