PackWriter: Reduce GC during enumeration

Instead of resizing an ArrayList until all objects have been added,
append objects into a specialized List type that uses small arrays
of 1024 entries for each 1024 objects added.

For a large repository like linux-2.6, PackWriter will now allocate
1,758 smaller arrays to hold the object list, without creating any
garbage from the intermediate states due to list expansion.

1024 was chosen as the block size (and initial directory size) as this
is a reasonable balance for the PackWriter code.  Each block uses
approximately 4096 bytes in a 32 bit JVM, as does the default top
level block directory.  The top level directory doesn't expand until 1
million items have been added to the list, which for linux-2.6 won't
yet occur as the lists are per-object-type and are thus bounded to
about 1/3 of 1.8 million.

Change-Id: If9e4092eb502394c5d3d044b58cf49952772f6d6
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 336 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/BlockListTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/BlockListTest.java
new file mode 100644
index 0000000000..7151af156a
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/BlockListTest.java
@@ -0,0 +1,336 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Iterator;
+
+import org.junit.Test;
+
+public class BlockListTest {
+	@Test
+	public void testEmptyList() {
+		BlockList<String> empty;
+
+		empty = new BlockList<String>();
+		assertEquals(0, empty.size());
+		assertTrue(empty.isEmpty());
+		assertFalse(empty.iterator().hasNext());
+
+		empty = new BlockList<String>(0);
+		assertEquals(0, empty.size());
+		assertTrue(empty.isEmpty());
+		assertFalse(empty.iterator().hasNext());
+
+		empty = new BlockList<String>(1);
+		assertEquals(0, empty.size());
+		assertTrue(empty.isEmpty());
+		assertFalse(empty.iterator().hasNext());
+
+		empty = new BlockList<String>(64);
+		assertEquals(0, empty.size());
+		assertTrue(empty.isEmpty());
+		assertFalse(empty.iterator().hasNext());
+	}
+
+	@Test
+	public void testGet() {
+		BlockList<String> list = new BlockList<String>(4);
+
+		try {
+			list.get(-1);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(-1), badIndex.getMessage());
+		}
+
+		try {
+			list.get(0);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(0), badIndex.getMessage());
+		}
+
+		try {
+			list.get(4);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(4), badIndex.getMessage());
+		}
+
+		String fooStr = "foo";
+		String barStr = "bar";
+		String foobarStr = "foobar";
+
+		list.add(fooStr);
+		list.add(barStr);
+		list.add(foobarStr);
+
+		assertSame(fooStr, list.get(0));
+		assertSame(barStr, list.get(1));
+		assertSame(foobarStr, list.get(2));
+
+		try {
+			list.get(3);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(3), badIndex.getMessage());
+		}
+	}
+
+	@Test
+	public void testSet() {
+		BlockList<String> list = new BlockList<String>(4);
+
+		try {
+			list.set(-1, "foo");
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(-1), badIndex.getMessage());
+		}
+
+		try {
+			list.set(0, "foo");
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(0), badIndex.getMessage());
+		}
+
+		try {
+			list.set(4, "foo");
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(4), badIndex.getMessage());
+		}
+
+		String fooStr = "foo";
+		String barStr = "bar";
+		String foobarStr = "foobar";
+
+		list.add(fooStr);
+		list.add(barStr);
+		list.add(foobarStr);
+
+		assertSame(fooStr, list.get(0));
+		assertSame(barStr, list.get(1));
+		assertSame(foobarStr, list.get(2));
+
+		assertSame(fooStr, list.set(0, barStr));
+		assertSame(barStr, list.set(1, fooStr));
+
+		assertSame(barStr, list.get(0));
+		assertSame(fooStr, list.get(1));
+
+		try {
+			list.set(3, "bar");
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(3), badIndex.getMessage());
+		}
+	}
+
+	@Test
+	public void testAddToEnd() {
+		BlockList<Integer> list = new BlockList<Integer>(4);
+		int cnt = BlockList.BLOCK_SIZE * 3;
+
+		for (int i = 0; i < cnt; i++)
+			list.add(Integer.valueOf(42 + i));
+		assertEquals(cnt, list.size());
+
+		for (int i = 0; i < cnt; i++)
+			assertEquals(Integer.valueOf(42 + i), list.get(i));
+
+		list.clear();
+		assertEquals(0, list.size());
+		assertTrue(list.isEmpty());
+
+		for (int i = 0; i < cnt; i++)
+			list.add(i, Integer.valueOf(42 + i));
+		assertEquals(cnt, list.size());
+
+		for (int i = 0; i < cnt; i++)
+			assertEquals(Integer.valueOf(42 + i), list.get(i));
+	}
+
+	@Test
+	public void testAddSlowPath() {
+		BlockList<String> list = new BlockList<String>(4);
+
+		String fooStr = "foo";
+		String barStr = "bar";
+		String foobarStr = "foobar";
+		String firstStr = "first";
+		String zeroStr = "zero";
+
+		list.add(fooStr);
+		list.add(barStr);
+		list.add(foobarStr);
+		assertEquals(3, list.size());
+
+		list.add(1, firstStr);
+		assertEquals(4, list.size());
+		assertSame(fooStr, list.get(0));
+		assertSame(firstStr, list.get(1));
+		assertSame(barStr, list.get(2));
+		assertSame(foobarStr, list.get(3));
+
+		list.add(0, zeroStr);
+		assertEquals(5, list.size());
+		assertSame(zeroStr, list.get(0));
+		assertSame(fooStr, list.get(1));
+		assertSame(firstStr, list.get(2));
+		assertSame(barStr, list.get(3));
+		assertSame(foobarStr, list.get(4));
+	}
+
+	@Test
+	public void testRemoveFromEnd() {
+		BlockList<String> list = new BlockList<String>(4);
+
+		String fooStr = "foo";
+		String barStr = "bar";
+		String foobarStr = "foobar";
+
+		list.add(fooStr);
+		list.add(barStr);
+		list.add(foobarStr);
+
+		assertSame(foobarStr, list.remove(2));
+		assertEquals(2, list.size());
+
+		assertSame(barStr, list.remove(1));
+		assertEquals(1, list.size());
+
+		assertSame(fooStr, list.remove(0));
+		assertEquals(0, list.size());
+	}
+
+	@Test
+	public void testRemoveSlowPath() {
+		BlockList<String> list = new BlockList<String>(4);
+
+		String fooStr = "foo";
+		String barStr = "bar";
+		String foobarStr = "foobar";
+
+		list.add(fooStr);
+		list.add(barStr);
+		list.add(foobarStr);
+
+		assertSame(barStr, list.remove(1));
+		assertEquals(2, list.size());
+		assertSame(fooStr, list.get(0));
+		assertSame(foobarStr, list.get(1));
+
+		assertSame(fooStr, list.remove(0));
+		assertEquals(1, list.size());
+		assertSame(foobarStr, list.get(0));
+
+		assertSame(foobarStr, list.remove(0));
+		assertEquals(0, list.size());
+	}
+
+	@Test
+	public void testAddRemoveAdd() {
+		BlockList<Integer> list = new BlockList<Integer>();
+		for (int i = 0; i < BlockList.BLOCK_SIZE + 1; i++)
+			list.add(Integer.valueOf(i));
+		assertEquals(Integer.valueOf(BlockList.BLOCK_SIZE),
+				list.remove(list.size() - 1));
+		assertEquals(Integer.valueOf(BlockList.BLOCK_SIZE - 1),
+				list.remove(list.size() - 1));
+		assertTrue(list.add(Integer.valueOf(1)));
+		assertEquals(Integer.valueOf(1), list.get(list.size() - 1));
+	}
+
+	@Test
+	public void testFastIterator() {
+		BlockList<Integer> list = new BlockList<Integer>(4);
+		int cnt = BlockList.BLOCK_SIZE * 3;
+
+		for (int i = 0; i < cnt; i++)
+			list.add(Integer.valueOf(42 + i));
+		assertEquals(cnt, list.size());
+
+		Iterator<Integer> itr = list.iterator();
+		for (int i = 0; i < cnt; i++) {
+			assertTrue(itr.hasNext());
+			assertEquals(Integer.valueOf(42 + i), itr.next());
+		}
+		assertFalse(itr.hasNext());
+	}
+
+	@Test
+	public void testAddRejectsBadIndexes() {
+		BlockList<Integer> list = new BlockList<Integer>(4);
+		list.add(Integer.valueOf(41));
+
+		try {
+			list.add(-1, Integer.valueOf(42));
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(-1), badIndex.getMessage());
+		}
+
+		try {
+			list.add(4, Integer.valueOf(42));
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(4), badIndex.getMessage());
+		}
+	}
+
+	@Test
+	public void testRemoveRejectsBadIndexes() {
+		BlockList<Integer> list = new BlockList<Integer>(4);
+		list.add(Integer.valueOf(41));
+
+		try {
+			list.remove(-1);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(-1), badIndex.getMessage());
+		}
+
+		try {
+			list.remove(4);
+		} catch (IndexOutOfBoundsException badIndex) {
+			assertEquals(String.valueOf(4), badIndex.getMessage());
+		}
+	}
+}