Implement atomic BatchRefUpdates for RefDirectory

The existing packed-refs file provides a mechanism for implementing
atomic multi-ref updates without any changes to the on-disk format or
lockfile protocol. We just need to make sure that there are no loose
refs involved in the transaction, which we can achieve by packing the
refs while holding locks on all loose refs. Full details of the
algorithm are in the PackedBatchRefUpdate javadoc.

This change does not implement reflog support, which will come in a
later change.

Change-Id: I09829544a0d4e8dbb141d28c748c3b96ef66fee1

1 files changed, 42 insertions, 8 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
index 4a4db12fbe..aa85cc7b29 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
@@ -82,8 +82,10 @@ public class BatchRefUpdate {
 	 * clock skew between machines on the same LAN using an NTP server also on
 	 * the same LAN should be under 5 seconds. 5 seconds is also not that long
 	 * for a large `git push` operation to complete.
+	 *
+	 * @since 4.9
 	 */
-	private static final Duration MAX_WAIT = Duration.ofSeconds(5);
+	protected static final Duration MAX_WAIT = Duration.ofSeconds(5);
 
 	private final RefDatabase refdb;
 
@@ -335,6 +337,19 @@ public class BatchRefUpdate {
 	}
 
 	/**
+	 * Set push options associated with this update.
+	 * <p>
+	 * Implementations must call this at the top of {@link #execute(RevWalk,
+	 * ProgressMonitor, List)}.
+	 *
+	 * @param options options passed to {@code execute}.
+	 * @since 4.9
+	 */
+	protected void setPushOptions(List<String> options) {
+		pushOptions = options;
+	}
+
+	/**
 	 * @return list of timestamps the batch must wait for.
 	 * @since 4.6
 	 */
@@ -400,7 +415,7 @@ public class BatchRefUpdate {
 		}
 
 		if (options != null) {
-			pushOptions = options;
+			setPushOptions(options);
 		}
 
 		monitor.beginTask(JGitText.get().updatingReferences, commands.size());
@@ -553,17 +568,36 @@ public class BatchRefUpdate {
 		return ref;
 	}
 
-	static Collection<String> getPrefixes(String s) {
+	/**
+	 * Get all path prefixes of a ref name.
+	 *
+	 * @param name
+	 *            ref name.
+	 * @return path prefixes of the ref name. For {@code refs/heads/foo}, returns
+	 *         {@code refs} and {@code refs/heads}.
+	 * @since 4.9
+	 */
+	protected static Collection<String> getPrefixes(String name) {
 		Collection<String> ret = new HashSet<>();
-		addPrefixesTo(s, ret);
+		addPrefixesTo(name, ret);
 		return ret;
 	}
 
-	static void addPrefixesTo(String s, Collection<String> out) {
-		int p1 = s.indexOf('/');
+	/**
+	 * Add prefixes of a ref name to an existing collection.
+	 *
+	 * @param name
+	 *            ref name.
+	 * @param out
+	 *            path prefixes of the ref name. For {@code refs/heads/foo},
+	 *            returns {@code refs} and {@code refs/heads}.
+	 * @since 4.9
+	 */
+	protected static void addPrefixesTo(String name, Collection<String> out) {
+		int p1 = name.indexOf('/');
 		while (p1 > 0) {
-			out.add(s.substring(0, p1));
-			p1 = s.indexOf('/', p1 + 1);
+			out.add(name.substring(0, p1));
+			p1 = name.indexOf('/', p1 + 1);
 		}
 	}