Optimize RefAdvertiser for wire protocol

The native wire protocol sends ref advertisements in the pkt-line
format, which requires encoding the ObjectId and ref name onto a byte
sequence.  Busy servers show this is a very high source of garbage,
which pushes the garbage collector harder when there are many refs in
the repository (e.g.  70k, in a Gerrit managed repository).

Optimize the side band advertiser by retaining the CharsetEncoder,
minimizing the amount of temporary garbage built during encoding.

Change-Id: I406c654bf82c1eb94b38862da2425e98396134cb

1 files changed, 74 insertions, 2 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
index f72a4b2b30..0cd720c29d 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefAdvertiser.java
@@ -43,9 +43,16 @@
 
 package org.eclipse.jgit.transport;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
 import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SYMREF;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.CharsetEncoder;
+import java.nio.charset.CoderResult;
 import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.Map;
@@ -64,8 +71,15 @@ import org.eclipse.jgit.util.RefMap;
 public abstract class RefAdvertiser {
 	/** Advertiser which frames lines in a {@link PacketLineOut} format. */
 	public static class PacketLineOutRefAdvertiser extends RefAdvertiser {
+		private final CharsetEncoder utf8 = UTF_8.newEncoder();
 		private final PacketLineOut pckOut;
 
+		private byte[] binArr = new byte[256];
+		private ByteBuffer binBuf = ByteBuffer.wrap(binArr);
+
+		private char[] chArr = new char[256];
+		private CharBuffer chBuf = CharBuffer.wrap(chArr);
+
 		/**
 		 * Create a new advertiser for the supplied stream.
 		 *
@@ -77,6 +91,64 @@ public abstract class RefAdvertiser {
 		}
 
 		@Override
+		public void advertiseId(AnyObjectId id, String refName)
+				throws IOException {
+			id.copyTo(binArr, 0);
+			binArr[OBJECT_ID_STRING_LENGTH] = ' ';
+			binBuf.position(OBJECT_ID_STRING_LENGTH + 1);
+			append(refName);
+			if (first) {
+				first = false;
+				if (!capablities.isEmpty()) {
+					append('\0');
+					for (String cap : capablities) {
+						append(' ');
+						append(cap);
+					}
+				}
+			}
+			append('\n');
+			pckOut.writePacket(binArr, 0, binBuf.position());
+		}
+
+		private void append(String str) throws CharacterCodingException {
+			int n = str.length();
+			if (n > chArr.length) {
+				chArr = new char[n + 256];
+				chBuf = CharBuffer.wrap(chArr);
+			}
+			str.getChars(0, n, chArr, 0);
+			chBuf.position(0).limit(n);
+			utf8.reset();
+			for (;;) {
+				CoderResult cr = utf8.encode(chBuf, binBuf, true);
+				if (cr.isOverflow()) {
+					grow();
+				} else if (cr.isUnderflow()) {
+					break;
+				} else {
+					cr.throwException();
+				}
+			}
+		}
+
+		private void append(int b) {
+			if (!binBuf.hasRemaining()) {
+				grow();
+			}
+			binBuf.put((byte) b);
+		}
+
+		private void grow() {
+			int cnt = binBuf.position();
+			byte[] tmp = new byte[binArr.length << 1];
+			System.arraycopy(binArr, 0, tmp, 0, cnt);
+			binArr = tmp;
+			binBuf = ByteBuffer.wrap(binArr);
+			binBuf.position(cnt);
+		}
+
+		@Override
 		protected void writeOne(final CharSequence line) throws IOException {
 			pckOut.writeString(line.toString());
 		}
@@ -91,7 +163,7 @@ public abstract class RefAdvertiser {
 
 	private final char[] tmpId = new char[Constants.OBJECT_ID_STRING_LENGTH];
 
-	private final Set<String> capablities = new LinkedHashSet<String>();
+	final Set<String> capablities = new LinkedHashSet<String>();
 
 	private final Set<ObjectId> sent = new HashSet<ObjectId>();
 
@@ -99,7 +171,7 @@ public abstract class RefAdvertiser {
 
 	private boolean derefTags;
 
-	private boolean first = true;
+	boolean first = true;
 
 	/**
 	 * Initialize this advertiser with a repository for peeling tags.