CommitGraph: add commit-graph for FileObjectDatabase

This change makes JGit can read .git/objects/info/commit-graph file
and then get CommitGraph.

Loading a new commit-graph into memory requires additional time. After
testing, loading a copy of the Linux's commit-graph(1039139 commits)
is under 50ms.

Bug: 574368
Change-Id: Iadfdd6ed437945d3cdfdbe988cf541198140a8bf
Signed-off-by: kylezhao <kylezhao@tencent.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ObjectDirectoryTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ObjectDirectoryTest.java
index 1a3b3787b1..b4ebdcdf8e 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ObjectDirectoryTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ObjectDirectoryTest.java
@@ -43,6 +43,7 @@
 package org.eclipse.jgit.internal.storage.file;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
@@ -251,6 +252,50 @@ public class ObjectDirectoryTest extends RepositoryTestCase {
 				IOException.class, () -> dir.getShallowCommits());
 	}
 
+	@Test
+	public void testGetCommitGraph() throws Exception {
+		db.getConfig().setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
+				ConfigConstants.CONFIG_COMMIT_GRAPH, true);
+		db.getConfig().setBoolean(ConfigConstants.CONFIG_GC_SECTION, null,
+				ConfigConstants.CONFIG_KEY_WRITE_COMMIT_GRAPH, true);
+
+		// no commit-graph
+		ObjectDirectory dir = db.getObjectDatabase();
+		assertTrue(dir.getCommitGraph().isEmpty());
+
+		// add commit-graph
+		commitFile("file.txt", "content", "master");
+		GC gc = new GC(db);
+		gc.gc();
+		File file = new File(db.getObjectsDirectory(),
+				Constants.INFO_COMMIT_GRAPH);
+		assertTrue(file.exists());
+		assertTrue(file.isFile());
+		assertTrue(dir.getCommitGraph().isPresent());
+		assertEquals(1, dir.getCommitGraph().get().getCommitCnt());
+
+		// update commit-graph
+		commitFile("file2.txt", "content", "master");
+		gc.gc();
+		assertEquals(2, dir.getCommitGraph().get().getCommitCnt());
+
+		// delete commit-graph
+		file.delete();
+		assertFalse(file.exists());
+		assertTrue(dir.getCommitGraph().isEmpty());
+
+		// commit-graph is corrupt
+		try (PrintWriter writer = new PrintWriter(file, UTF_8.name())) {
+			writer.println("this is a corrupt commit-graph");
+		}
+		assertTrue(dir.getCommitGraph().isEmpty());
+
+		// add commit-graph again
+		gc.gc();
+		assertTrue(dir.getCommitGraph().isPresent());
+		assertEquals(2, dir.getCommitGraph().get().getCommitCnt());
+	}
+
 	private Collection<Callable<ObjectId>> blobInsertersForTheSameFanOutDir(
 			final ObjectDirectory dir) {
 		Callable<ObjectId> callable = () -> dir.newInserter()