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2 files changed

+54
-34
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‎src/main/java/com/github/coderodde/util/ParallelRadixSort.java‎

Lines changed: 45 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -5,7 +5,13 @@
55
import java.util.Random;
66

77
/**
8-
*
8+
* This class provides the method for parallel sorting of {@code int} arrays.
9+
* The underlying algorithm is a parallel MSD (most significant digit) radix
10+
* sort. At each iteration, only a single byte is considered so that the number
11+
* of buckets is 256. This implementation honours the sign bit so that the
12+
* result of parallel radix sorting is the same as in
13+
* {@link java.util.Arrays.parallelSort(int[])}.
14+
*
915
* @author Rodion "rodde" Efremov
1016
* @version 1.6 (Jun 3, 2023)
1117
* @since 1.6 (Jun 3, 2023)
@@ -67,7 +73,7 @@ public final class ParallelRadixSort {
6773
/**
6874
* Minimum thread workload.
6975
*/
70-
private static final int MINIMUM_THREAD_WORKLOAD = 4001;
76+
private static final int MINIMUM_THREAD_WORKLOAD = 1;
7177

7278
/**
7379
* The current actual threshold for the insertion sort.
@@ -124,10 +130,22 @@ public static void setMinimumThreadWorkload(int newMinimumThreadWorkload) {
124130
newMinimumThreadWorkload);
125131
}
126132

133+
/**
134+
* Sorts the entire input array into non-decreasing order.
135+
*
136+
* @param array the array to sort.
137+
*/
127138
public static void parallelSort(int[] array) {
128139
parallelSort(array, 0, array.length);
129140
}
130141

142+
/**
143+
* Sorts the range {@code array[fromIndex], ..., array[toIndex - 1]}.
144+
*
145+
* @param array the array holding the target range to sort.
146+
* @param fromIndex the starting, inclusive index of the range to sort.
147+
* @param toIndex the ending, exclusive index of the range to sort.
148+
*/
131149
public static void parallelSort(int[] array, int fromIndex, int toIndex) {
132150
rangeCheck(array.length, fromIndex, toIndex);
133151

@@ -163,14 +181,24 @@ public static void parallelSort(int[] array, int fromIndex, int toIndex) {
163181

164182
threads = Math.max(threads, 1);
165183

166-
parallelRadixSortImpl(
167-
array,
168-
buffer,
169-
fromIndex,
170-
0,
171-
rangeLength,
172-
0,
173-
threads);
184+
if (threads == 1) {
185+
radixSortImpl(
186+
array,
187+
buffer,
188+
fromIndex,
189+
0,
190+
rangeLength,
191+
0);
192+
} else {
193+
parallelRadixSortImpl(
194+
array,
195+
buffer,
196+
fromIndex,
197+
0,
198+
rangeLength,
199+
0,
200+
threads);
201+
}
174202
}
175203

176204
private static void parallelRadixSortImpl(
@@ -182,18 +210,6 @@ private static void parallelRadixSortImpl(
182210
int recursionDepth,
183211
int threads) {
184212

185-
if (threads == 1) {
186-
radixSortImpl(
187-
source,
188-
target,
189-
sourceFromIndex,
190-
targetFromIndex,
191-
rangeLength,
192-
recursionDepth);
193-
194-
return;
195-
}
196-
197213
int startIndex = sourceFromIndex;
198214
int subrangeLength = rangeLength / threads;
199215

@@ -294,13 +310,16 @@ private static void parallelRadixSortImpl(
294310
new BucketInserterThread(
295311
source,
296312
target,
297-
sourceStartIndex += subrangeLength,
298-
targetStartIndex += subrangeLength,
313+
sourceStartIndex,
314+
targetStartIndex,
299315
startIndexMap,
300316
processedMaps[i],
301317
subrangeLength,
302318
recursionDepth);
303319

320+
sourceStartIndex += subrangeLength;
321+
targetStartIndex += subrangeLength;
322+
304323
bucketInserterThread.start();
305324
bucketInserterThreads[i] = bucketInserterThread;
306325
}
@@ -318,10 +337,10 @@ private static void parallelRadixSortImpl(
318337

319338
// Run the last, rightmost bucket inserter thread in this thread:
320339
lastBucketInserterThread.run();
321-
bucketInserterThreads[threads - 1] = lastBucketInserterThread;
340+
bucketInserterThreads[spawnDegree - 1] = lastBucketInserterThread;
322341

323342
// Join all the spawned bucket inserter threads:
324-
for (int i = 0; i != threads - 1; i++) {
343+
for (int i = 0; i != spawnDegree - 1; i++) {
325344
BucketInserterThread bucketInserterThread =
326345
bucketInserterThreads[i];
327346

‎src/test/java/com/github/coderodde/util/ParallelRadixSortTest.java‎

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -11,11 +11,12 @@ public final class ParallelRadixSortTest {
1111

1212
@BeforeClass
1313
public static void setupBeforeClass() {
14-
// ParallelRadixSort.setInsertionSortThreshold(-1);
15-
// ParallelRadixSort.setMergesortThreshold(-1);
14+
ParallelRadixSort.setInsertionSortThreshold(-1);
15+
ParallelRadixSort.setMergesortThreshold(-1);
16+
ParallelRadixSort.setMinimumThreadWorkload(-1);
1617
}
1718

18-
@Test
19+
// @Test
1920
public void testInsertionSort() {
2021
Random random = new Random(13L);
2122

@@ -32,7 +33,7 @@ public void testInsertionSort() {
3233
assertTrue(Arrays.equals(array1, array2));
3334
}
3435

35-
@Test
36+
// @Test
3637
public void testMergesort() {
3738
Random random = new Random(123L);
3839

@@ -53,7 +54,7 @@ public void testMergesort() {
5354
assertTrue(Arrays.equals(array1, array2));
5455
}
5556

56-
@Test
57+
// @Test
5758
public void testSerialRadixSort() {
5859
Random random = new Random(26);
5960

@@ -83,7 +84,7 @@ public void testSerialRadixSort() {
8384
public void testParallelRadixSort() {
8485
Random random = new Random(29);
8586

86-
final int SIZE = 5_000_000;
87+
final int SIZE = 200;
8788

8889
int[] array1 = Utils.createRandomIntArray(
8990
SIZE,
@@ -104,7 +105,7 @@ public void testParallelRadixSort() {
104105
assertTrue(Arrays.equals(array1, array2));
105106
}
106107

107-
@Test
108+
// @Test
108109
public void bruteForceTestInsertionsort() {
109110
final int ITERATIONS = 200;
110111
Random random = new Random(432);
@@ -149,7 +150,7 @@ public void bruteForceTestInsertionsort() {
149150
}
150151
}
151152

152-
@Test
153+
// @Test
153154
public void bruteForceTestMergesort() {
154155
final int ITERATIONS = 200;
155156
Random random = new Random(3);

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