這是桶排序的Java 平行計算版本，隨著生成的隨機整數的復雜度增加，也就是生成區間的不斷擴大，加速比會明顯增長。數據樣本太簡單的話，無法體現平行計算的威力。特此聲明：桶排序平行化的基本思路來自于： Professor Ian Bond in Massey University. 初始版本用CPP+MPI 編寫，我本人用Java重寫了基本算法，而且增加了自己的算法，數據進桶等比例縮小和出桶時的等比例放大. 目前，只開了4個線程，讀者可以根據自身情況手動增加線程，但是需要修改代碼。你不能用循環動態建立線程，很慢！
這是初始版本，后期需要優化，也就是繼續加速，增大加速比. 平行化是否成功的關鍵就是看加速比：linear time / parallel time

-Xms18024M -Xmx18024M
請注意，推薦內存 32 G，你可以根據自己的內存調整隨機整數生成區間，當心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 bucketsortint[] 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 bucketsortstore_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;}@Overridepublic 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 bucketsortint[] store_array = new int[max+1];for (int i = 0; i < original_array.length; i++) {// empty item in array is : 0if (original_array[i]!=0){// 71 -> 21 , 89->14 , save physical memoryint int_num = shrink_number(original_array[i],bucket_num,bucket_size);// here is the miracle of bucketsortstore_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.... 1-25,26-50,51-75,76-100for (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 parallelSmallBucketThread 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 sdouble 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 billionint num_trails = 100000000; // 100 millionTestBucketSort 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));} }

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