Avoid ArrayList<Integer> boxing when collecting ParNew promotion-failure sizes

parser/src/main/java/com/microsoft/gctoolkit/parser/GenerationalHeapParser.java

@@ -39,6 +39,7 @@
 
 import java.util.AbstractMap;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Optional;
 import java.util.Set;
 import java.util.function.BiConsumer;
@@ -622,16 +623,17 @@ public void parNewPromotionFailedDetails(GCLogTrace trace, String line) {
         scavengeTimeStamp = getClock();
         garbageCollectionTypeForwardReference = GarbageCollectionTypes.ParNewPromotionFailed;
         gcCauseForwardReference = GCCause.PROMOTION_FAILED;
-        ArrayList<Integer> blocks = new ArrayList<>();
+        int[] blocks = new int[4];
+        int blockCount = 0;
         GCLogTrace block = PARNEW_PROMOTION_FAILURE_SIZE_BLOCK.parse(line);
         if (block != null) {
             do {
-                blocks.add(block.getIntegerGroup(1));
+                if (blockCount == blocks.length)
+                    blocks = Arrays.copyOf(blocks, blocks.length * 2);
+                blocks[blockCount++] = block.getIntegerGroup(1);
             } while (block.hasNext());
         }
-        promotionFailureSizesForwardReference = new int[blocks.size()];
-        for (int index = 0; index < blocks.size(); index++)
-            promotionFailureSizesForwardReference[index] = blocks.get(index);
+        promotionFailureSizesForwardReference = Arrays.copyOf(blocks, blockCount);
         GCLogTrace memorySummary = BEFORE_AFTER_CONFIGURED_PAUSE_RULE.parse(line);
         youngMemoryPoolSummaryForwardReference = memorySummary.getOccupancyBeforeAfterWithMemoryPoolSizeSummary(1);
         scavengeDurationForwardReference = memorySummary.getDuration();

parser/src/test/java/com/microsoft/gctoolkit/parser/GenerationalHeapParserPromotionFailedDetailsTest.java

@@ -0,0 +1,56 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+package com.microsoft.gctoolkit.parser;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+/**
+ * Locks the behavior of GenerationalHeapParser#parNewPromotionFailedDetails, which collects the
+ * per-thread promotion failure sizes found on a "ParNew (N: promotion failure size = X) ..." line.
+ * These characterizations pin the exact values, order, and count produced for zero, one, and many
+ * promotion failure size blocks so that the underlying collection strategy can be safely changed.
+ */
+public class GenerationalHeapParserPromotionFailedDetailsTest {
+
+    private int[] promotionFailureSizesOf(GenerationalHeapParser parser) throws ReflectiveOperationException {
+        Field field = GenerationalHeapParser.class.getDeclaredField("promotionFailureSizesForwardReference");
+        field.setAccessible(true);
+        return (int[]) field.get(parser);
+    }
+
+    @Test
+    public void singlePromotionFailureSizeIsCaptured() throws ReflectiveOperationException {
+        GenerationalHeapParser parser = new GenerationalHeapParser();
+        String line = "2015-05-26T12:23:33.483-0700: 4.484: [ParNew (0: promotion failure size = 8)  (promotion failed): 19136K->19136K(19136K), 0.0300000 secs]";
+
+        parser.parNewPromotionFailedDetails(null, line);
+
+        assertArrayEquals(new int[]{8}, promotionFailureSizesOf(parser));
+    }
+
+    @Test
+    public void multiplePromotionFailureSizesArePreservedInOrder() throws ReflectiveOperationException {
+        GenerationalHeapParser parser = new GenerationalHeapParser();
+        String line = "2017-04-16T12:35:12.797-0700: 142237.056: [ParNew (0: promotion failure size = 3)  (1: promotion failure size = 3)  (2: promotion failure size = 3)  (3: promotion failure size = 3)  (4: promotion failure size = 3)  (5: promotion failure size = 3)  (6: promotion failure size = 3)  (7: promotion failure size = 131074)  (8: promotion failure size = 3)  (9: promotion failure size = 3)  (10: promotion failure size = 3)  (11: promotion failure size = 3)  (12: promotion failure size = 3)  (13: promotion failure size = 3)  (14: promotion failure size = 3)  (15: promotion failure size = 3)  (16: promotion failure size = 3)  (17: promotion failure size = 3)  (18: promotion failure size = 3)  (19: promotion failure size = 3)  (20: promotion failure size = 3)  (21: promotion failure size = 3)  (22: promotion failure size = 3)  (23: promotion failure size = 3)  (24: promotion failure size = 3)  (25: promotion failure size = 4)  (26: promotion failure size = 3)  (27: promotion failure size = 3)  (promotion failed): 1611303K->1607853K(1800000K), 0.4413433 secs]";
+
+        parser.parNewPromotionFailedDetails(null, line);
+
+        int[] expected = {3, 3, 3, 3, 3, 3, 3, 131074, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3};
+        assertArrayEquals(expected, promotionFailureSizesOf(parser));
+    }
+
+    @Test
+    public void noPromotionFailureSizeBlockYieldsEmptyArrayInsteadOfThrowing() throws ReflectiveOperationException {
+        GenerationalHeapParser parser = new GenerationalHeapParser();
+        String line = "2014-10-24T06:04:47.413-0400: 748196.080: [ParNew (promotion failed): 19136K->19136K(19136K), 0.0300000 secs]";
+
+        assertDoesNotThrow(() -> parser.parNewPromotionFailedDetails(null, line));
+
+        assertArrayEquals(new int[0], promotionFailureSizesOf(parser));
+    }
+}