IndexPack: Defer the "Resolving deltas" progress meter

If delta resolution completes in < 1000 milliseconds, don't bother
showing the progress meter. This is actually very common for a Gerrit
Code Review server, where the client is probably sending 1 commit and
only a few trees/blobs modified... and the base objects are hot in the
process buffer cache.

The 1000 millisecond delay is just a guess at a reasonable time to wait.

Change-Id: I440baa64ab0dfa21be61deae8dcd3ca061bed8ce
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/transport/PackParser.java

@@ -54,6 +54,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
@@ -61,6 +62,7 @@ import org.eclipse.jgit.JGitText;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.BatchingProgressMonitor;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.InflaterCache;
 import org.eclipse.jgit.lib.MutableObjectId;
@@ -478,6 +480,11 @@ public abstract class PackParser {
 			if (!deferredCheckBlobs.isEmpty())
 				doDeferredCheckBlobs();
 			if (deltaCount > 0) {
+				if (resolving instanceof BatchingProgressMonitor) {
+					((BatchingProgressMonitor) resolving).setDelayStart(
+							1000,
+							TimeUnit.MILLISECONDS);
+				}
 				resolving.beginTask(JGitText.get().resolvingDeltas, deltaCount);
 				resolveDeltas(resolving);
 				if (entryCount < objectCount) {