Optimize RefAdvertiser performance by avoiding sorting

Don't copy and sort the set of references if they are passed through
in a RefMap or a SortedMap using the key's natural sort ordering.
Either map is already in the order we want to present the items
to the client in, so copying and sorting is a waste of local CPU
and memory.

Change-Id: I49ada7c1220e0fc2a163b9752c2b77525d9c82c1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.http.server/src/org/eclipse/jgit/http/server/InfoRefsServlet.java

@@ -99,7 +99,7 @@ class InfoRefsServlet extends HttpServlet {
 
 		Map<String, Ref> refs = db.getAllRefs();
 		refs.remove(Constants.HEAD);
-		adv.send(refs.values());
+		adv.send(refs);
 		return out.toString().getBytes(Constants.CHARACTER_ENCODING);
 	}
 }

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

@@ -591,7 +591,7 @@ public class ReceivePack {
 			adv.advertiseCapability(CAPABILITY_OFS_DELTA);
 		refs = db.getAllRefs();
 		final Ref head = refs.remove(Constants.HEAD);
-		adv.send(refs.values());
+		adv.send(refs);
 		if (!head.isSymbolic())
 			adv.advertiseHave(head.getObjectId());
 		adv.includeAdditionalHaves();

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

@@ -44,9 +44,10 @@
 package org.eclipse.jgit.transport;
 
 import java.io.IOException;
-import java.util.Collection;
 import java.util.LinkedHashSet;
+import java.util.Map;
 import java.util.Set;
+import java.util.SortedMap;
 
 import org.eclipse.jgit.lib.AlternateRepositoryDatabase;
 import org.eclipse.jgit.lib.AnyObjectId;
@@ -59,6 +60,7 @@ import org.eclipse.jgit.revwalk.RevFlag;
 import org.eclipse.jgit.revwalk.RevObject;
 import org.eclipse.jgit.revwalk.RevTag;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.util.RefMap;
 
 /** Support for the start of {@link UploadPack} and {@link ReceivePack}. */
 public abstract class RefAdvertiser {
@@ -122,7 +124,7 @@ public abstract class RefAdvertiser {
 	 * <p>
 	 * This method must be invoked prior to any of the following:
 	 * <ul>
-	 * <li>{@link #send(Collection)}
+	 * <li>{@link #send(Map)}
 	 * <li>{@link #advertiseHave(AnyObjectId)}
 	 * <li>{@link #includeAdditionalHaves()}
 	 * </ul>
@@ -140,7 +142,7 @@ public abstract class RefAdvertiser {
 	 * <p>
 	 * This method must be invoked prior to any of the following:
 	 * <ul>
-	 * <li>{@link #send(Collection)}
+	 * <li>{@link #send(Map)}
 	 * <li>{@link #advertiseHave(AnyObjectId)}
 	 * <li>{@link #includeAdditionalHaves()}
 	 * </ul>
@@ -160,14 +162,14 @@ public abstract class RefAdvertiser {
 	 *
 	 * @param refs
 	 *            zero or more refs to format for the client. The collection is
-	 *            copied and sorted before display and therefore may appear in
+	 *            sorted before display if necessary, and therefore may appear
-	 *            any order.
+	 *            in any order.
 	 * @throws IOException
 	 *             the underlying output stream failed to write out an
 	 *             advertisement record.
 	 */
-	public void send(final Collection<Ref> refs) throws IOException {
+	public void send(final Map<String, Ref> refs) throws IOException {
-		for (final Ref r : RefComparator.sort(refs)) {
+		for (final Ref r : getSortedRefs(refs)) {
 			final RevObject obj = parseAnyOrNull(r.getObjectId());
 			if (obj != null) {
 				advertiseAny(obj, r.getName());
@@ -177,6 +179,13 @@ public abstract class RefAdvertiser {
 		}
 	}
 
+	private Iterable<Ref> getSortedRefs(Map<String, Ref> all) {
+		if (all instanceof RefMap
+				|| (all instanceof SortedMap && ((SortedMap) all).comparator() == null))
+			return all.values();
+		return RefComparator.sort(all.values());
+	}
+
 	/**
 	 * Advertise one object is available using the magic {@code .have}.
 	 * <p>

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2009, Google Inc.
+ * Copyright (C) 2008-2010, Google Inc.
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
@@ -330,7 +330,7 @@ public class UploadPack {
 		adv.advertiseCapability(OPTION_NO_PROGRESS);
 		adv.setDerefTags(true);
 		refs = db.getAllRefs();
-		adv.send(refs.values());
+		adv.send(refs);
 		adv.end();
 	}