BitmapIndex: Add interface to track bitmaps found (or not)

We want to know what objects had bitmaps in the walk of the
request. We can check their position in the history and evaluate our
bitmap selection algorithm.

Introduce a listener interface to the BitmapIndex to report which
getBitmap() calls returned a bitmap (or not) and a method to the
bitmap index to set the listener.

Change-Id: Iac8fcc1539ddd2dd450e8a1cf5a5b1089679c378

1 files changed, 85 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/BitmapIndexTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/BitmapIndexTest.java
new file mode 100644
index 0000000000..ee4fa8bcc7
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/BitmapIndexTest.java
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2024, Google Inc. and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.lib;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import org.eclipse.jgit.internal.storage.file.FileRepository;
+import org.eclipse.jgit.internal.storage.file.GC;
+import org.eclipse.jgit.junit.LocalDiskRepositoryTestCase;
+import org.eclipse.jgit.junit.TestRepository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.junit.Before;
+import org.junit.Test;
+
+public class BitmapIndexTest extends LocalDiskRepositoryTestCase {
+
+  private static final String MAIN = "refs/heads/main";
+
+  TestRepository<FileRepository> repo;
+
+  RevCommit tipWithBitmap;
+
+  @Override
+  @Before
+  public void setUp() throws Exception {
+    super.setUp();
+    FileRepository db = createWorkRepository();
+    repo = new TestRepository<>(db);
+
+    RevCommit base = repo.commit().create();
+    RevCommit one = repo.commit().parent(base).create();
+    tipWithBitmap = repo.commit().parent(one).create();
+    repo.update(MAIN, tipWithBitmap);
+
+    GC gc = new GC(repo.getRepository());
+    gc.setAuto(false);
+    gc.gc().get();
+
+    assertNotNull(repo.getRevWalk().getObjectReader().getBitmapIndex());
+  }
+
+
+  @Test
+  public void listener_getBitmap_counted() throws Exception {
+    try (RevWalk rw = repo.getRevWalk();
+        ObjectReader or = rw.getObjectReader()) {
+      BitmapLookupCounter counter = new BitmapLookupCounter();
+      BitmapIndex bitmapIndex = or.getBitmapIndex();
+      bitmapIndex.addBitmapLookupListener(counter);
+
+      bitmapIndex.getBitmap(tipWithBitmap);
+      bitmapIndex.getBitmap(tipWithBitmap);
+      bitmapIndex.getBitmap(ObjectId.zeroId());
+
+      assertEquals(2, counter.bitmapFound);
+      assertEquals(1, counter.bitmapNotFound);
+    }
+  }
+
+	private static class BitmapLookupCounter
+			implements BitmapIndex.BitmapLookupListener {
+		int bitmapFound = 0;
+
+		int bitmapNotFound = 0;
+
+		@Override
+		public void onBitmapFound(AnyObjectId oid) {
+			bitmapFound += 1;
+		}
+
+		@Override
+		public void onBitmapNotFound(AnyObjectId oid) {
+			bitmapNotFound += 1;
+		}
+	}
+}
\ No newline at end of file