Only increment mod count if packed-refs file changes

Previously if a packed-refs file was racily clean then there
was a 2.5 second window in which each call to getPackedRefs
would increment the mod count causing a RefsChangedEvent to be
fired since the FileSnapshot would report the file as modified.

If a RefsChangedListener called getRef/getRefs from the
onRefsChanged method then a StackOverflowError could occur
since the stack could be exhausted before the 2.5 second
window expired and the packed-refs file would no longer
report being modified.

Now a SHA-1 is computed of the packed-refs file and the
mod count is only incremented when the packed refs are
successfully set and the id of the new packed-refs file
does not match the id of the old packed-refs file.

Change-Id: I8cab6e5929479ed748812b8598c7628370e79697

1 files changed, 32 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/RefDirectoryTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/RefDirectoryTest.java
index 3ca4f589db..508b690509 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/RefDirectoryTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/RefDirectoryTest.java
@@ -60,6 +60,8 @@ import static org.junit.Assert.fail;
 import java.io.File;
 import java.io.IOException;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.eclipse.jgit.events.ListenerHandle;
 import org.eclipse.jgit.events.RefsChangedEvent;
@@ -1077,6 +1079,36 @@ public class RefDirectoryTest extends LocalDiskRepositoryTestCase {
 		assertSame(master_p2, refdir.peel(master_p2));
 	}
 
+	@Test
+	public void testRefsChangedStackOverflow() throws Exception {
+		final FileRepository newRepo = createBareRepository();
+		final RefDatabase refDb = newRepo.getRefDatabase();
+		File packedRefs = new File(newRepo.getDirectory(), "packed-refs");
+		assertTrue(packedRefs.createNewFile());
+		final AtomicReference<StackOverflowError> error = new AtomicReference<StackOverflowError>();
+		final AtomicReference<IOException> exception = new AtomicReference<IOException>();
+		final AtomicInteger changeCount = new AtomicInteger();
+		newRepo.getListenerList().addRefsChangedListener(
+				new RefsChangedListener() {
+
+					public void onRefsChanged(RefsChangedEvent event) {
+						try {
+							refDb.getRefs("ref");
+							changeCount.incrementAndGet();
+						} catch (StackOverflowError soe) {
+							error.set(soe);
+						} catch (IOException ioe) {
+							exception.set(ioe);
+						}
+					}
+				});
+		refDb.getRefs("ref");
+		refDb.getRefs("ref");
+		assertNull(error.get());
+		assertNull(exception.get());
+		assertEquals(1, changeCount.get());
+	}
+
 	private void writeLooseRef(String name, AnyObjectId id) throws IOException {
 		writeLooseRef(name, id.name() + "\n");
 	}