Fix memory leak in dfs.DeltaBaseCase

The LRU chain management code was broken leading to situations where
the chain was incomplete.  This prevented the cache from removing
items when it exceeded its memory target, causing a leak.

One case was repeated hit on the head of the chain. moveToHead(e)
was invoked linking the head back to itself in a cycle orphaning
the rest of the table.

Add some unit tests to cover this and a few other paths.

Change-Id: Ib27486eaa1b1d2bf1c745a56d0a5832bfb029322

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DeltaBaseCacheTest.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2015, 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.internal.storage.dfs;
+
+import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+
+import org.eclipse.jgit.internal.storage.dfs.DeltaBaseCache.Entry;
+import org.eclipse.jgit.junit.TestRng;
+import org.junit.Before;
+import org.junit.Test;
+
+public class DeltaBaseCacheTest {
+	private static final int SZ = 512;
+
+	private DfsPackKey key;
+	private DeltaBaseCache cache;
+	private TestRng rng;
+
+	@Before
+	public void setUp() {
+		key = new DfsPackKey();
+		cache = new DeltaBaseCache(SZ);
+		rng = new TestRng(getClass().getSimpleName());
+	}
+
+	@Test
+	public void testObjectLargerThanCacheDoesNotEvict() {
+		byte[] obj12 = put(12, 32);
+		put(24, SZ + 5);
+		assertNull("does not store large object", cache.get(key, 24));
+		get(obj12, 12);
+	}
+
+	@Test
+	public void testCacheLruExpires1() {
+		byte[] obj1 = put(1, SZ / 4);
+		put(2, SZ / 4);
+		byte[] obj3 = put(3, SZ / 4);
+		put(4, SZ / 4);
+		assertEquals(SZ, cache.getMemoryUsed());
+
+		get(obj3, 3);
+		get(obj1, 1);
+		put(5, SZ / 2);
+		assertEquals(SZ, cache.getMemoryUsed());
+		assertEquals(SZ, cache.getMemoryUsedByTableForTest());
+		assertEquals(SZ, cache.getMemoryUsedByLruChainForTest());
+		assertNull(cache.get(key, 4));
+		assertNull(cache.get(key, 2));
+
+		get(obj1, 1);
+		get(obj3, 3);
+	}
+
+	@Test
+	public void testCacheLruExpires2() {
+		int pos0 = (0 << 10) | 2;
+		int pos1 = (1 << 10) | 2;
+		int pos2 = (2 << 10) | 2;
+		int pos5 = (5 << 10) | 2;
+		int pos6 = (6 << 10) | 2;
+
+		put(pos0, SZ / 4);
+		put(pos5, SZ / 4);
+		byte[] obj1 = put(pos1, SZ / 4);
+		byte[] obj2 = put(pos2, SZ / 4);
+		assertEquals(SZ, cache.getMemoryUsed());
+
+		byte[] obj6 = put(pos6, SZ / 2);
+		assertEquals(SZ, cache.getMemoryUsed());
+		assertEquals(SZ, cache.getMemoryUsedByTableForTest());
+		assertEquals(SZ, cache.getMemoryUsedByLruChainForTest());
+		assertNull(cache.get(key, pos0));
+		assertNull(cache.get(key, pos5));
+
+		get(obj1, pos1);
+		get(obj2, pos2);
+		get(obj6, pos6);
+	}
+
+	@Test
+	public void testCacheMemoryUsedConsistentWithExpectations() {
+		put(1, 32);
+		put(2, 32);
+		put(3, 32);
+
+		assertNotNull(cache.get(key, 1));
+		assertNotNull(cache.get(key, 1));
+
+		assertEquals(32 * 3, cache.getMemoryUsed());
+		assertEquals(32 * 3, cache.getMemoryUsedByTableForTest());
+		assertEquals(32 * 3, cache.getMemoryUsedByLruChainForTest());
+	}
+
+	private void get(byte[] data, int position) {
+		Entry e = cache.get(key, position);
+		assertNotNull("expected entry at " + position, e);
+		assertEquals("expected blob for " + position, OBJ_BLOB, e.type);
+		assertSame("expected data for " + position, data, e.data);
+	}
+
+	private byte[] put(int position, int sz) {
+		byte[] data = rng.nextBytes(sz);
+		cache.put(key, position, OBJ_BLOB, data);
+		return data;
+	}
+}

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DeltaBaseCache.java

@@ -70,8 +70,11 @@ final class DeltaBaseCache {
 	private int curByteCount;
 
 	DeltaBaseCache(DfsReader reader) {
-		DfsReaderOptions options = reader.getOptions();
-		maxByteCount = options.getDeltaBaseCacheLimit();
+		this(reader.getOptions().getDeltaBaseCacheLimit());
+	}
+
+	DeltaBaseCache(int maxBytes) {
+		maxByteCount = maxBytes;
 		table = new Slot[1 << TABLE_BITS];
 	}
 
@@ -84,6 +87,7 @@ final class DeltaBaseCache {
 					moveToHead(e);
 					return buf;
 				}
+				return null;
 			}
 		}
 		return null;
@@ -101,23 +105,15 @@ final class DeltaBaseCache {
 		e.data = new SoftReference<Entry>(new Entry(data, objectType));
 		e.tableNext = table[tableIdx];
 		table[tableIdx] = e;
-		moveToHead(e);
+		lruPushHead(e);
 	}
 
 	private void releaseMemory() {
 		while (curByteCount > maxByteCount && lruTail != null) {
-			Slot currOldest = lruTail;
-			Slot nextOldest = currOldest.lruPrev;
-
-			curByteCount -= currOldest.size;
-			unlink(currOldest);
-			removeFromTable(currOldest);
-
-			if (nextOldest == null)
-				lruHead = null;
-			else
-				nextOldest.lruNext = null;
-			lruTail = nextOldest;
+			Slot e = lruTail;
+			curByteCount -= e.size;
+			lruRemove(e);
+			removeFromTable(e);
 		}
 	}
 
@@ -136,27 +132,68 @@ final class DeltaBaseCache {
 				return;
 			}
 		}
+
+		throw new IllegalStateException(String.format(
+				"entry for %s:%d not in table", //$NON-NLS-1$
+				e.pack, Long.valueOf(e.offset)));
 	}
 
 	private void moveToHead(final Slot e) {
-		unlink(e);
-		e.lruPrev = null;
-		e.lruNext = lruHead;
-		if (lruHead != null)
-			lruHead.lruPrev = e;
+		if (e != lruHead) {
+			lruRemove(e);
+			lruPushHead(e);
+		}
+	}
+
+	private void lruRemove(final Slot e) {
+		Slot p = e.lruPrev;
+		Slot n = e.lruNext;
+
+		if (p != null) {
+			p.lruNext = n;
+		} else {
+			lruHead = n;
+		}
+
+		if (n != null) {
+			n.lruPrev = p;
+		} else {
+			lruTail = p;
+		}
+	}
+
+	private void lruPushHead(final Slot e) {
+		Slot n = lruHead;
+		e.lruNext = n;
+		if (n != null)
+			n.lruPrev = e;
 		else
 			lruTail = e;
+
+		e.lruPrev = null;
 		lruHead = e;
 	}
 
-	private void unlink(final Slot e) {
-		Slot prev = e.lruPrev;
-		Slot next = e.lruNext;
+	int getMemoryUsed() {
+		return curByteCount;
+	}
+
+	int getMemoryUsedByLruChainForTest() {
+		int r = 0;
+		for (Slot e = lruHead; e != null; e = e.lruNext) {
+			r += e.size;
+		}
+		return r;
+	}
 
-		if (prev != null)
-			prev.lruNext = next;
-		if (next != null)
-			next.lruPrev = prev;
+	int getMemoryUsedByTableForTest() {
+		int r = 0;
+		for (int i = 0; i < table.length; i++) {
+			for (Slot e = table[i]; e != null; e = e.tableNext) {
+				r += e.size;
+			}
+		}
+		return r;
 	}
 
 	static class Entry {