Reuse the line buffer between strings in PacketLineIn

When reading pkt-lines off an InputStream we are quite likely to
consume a whole group of fairly short lines in rapid succession, such
as in the have exchange that occurs in the fetch-pack/upload-pack
protocol.  Rather than allocating a throwaway buffer for each
line's raw byte sequence, reuse a buffer that is equal to the small
side-band packet size, which is 1000 bytes.  Text based pkt-lines
are required to be less than this size because many widely deployed
versions of C Git use a statically allocated array of this length.

Change-Id: Ia5c8e95b85020f7f80b6d269dda5059b092d274d
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
index 1022eb2ee11a6a61bdc2e1bd046ad82a23d0d894..170e4ddbe06337a68b7dfde88d5bb2c33e6864cb 100644 (file)
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PacketLineIn.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2009, Google Inc.
+ * Copyright (C) 2008-2010, Google Inc.
  * Copyright (C) 2008-2009, Robin Rosenberg <robin.rosenberg@dewire.com>
  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
  * and other copyright owners as documented in the project's IP log.
@@ -72,11 +72,11 @@ class PacketLineIn {
 
        private final InputStream in;
 
-       private final byte[] lenbuffer;
+       private final byte[] lineBuffer;
 
        PacketLineIn(final InputStream i) {
                in = i;
-               lenbuffer = new byte[4];
+               lineBuffer = new byte[SideBandOutputStream.SMALL_BUF];
        }
 
        AckNackResult readACK(final MutableObjectId returnedId) throws IOException {
@@ -124,22 +124,27 @@ class PacketLineIn {
 
                len -= 4; // length header (4 bytes)
 
-               final byte[] raw = new byte[len];
+               byte[] raw;
+               if (len <= lineBuffer.length)
+                       raw = lineBuffer;
+               else
+                       raw = new byte[len];
+
                IO.readFully(in, raw, 0, len);
                return RawParseUtils.decode(Constants.CHARSET, raw, 0, len);
        }
 
        int readLength() throws IOException {
-               IO.readFully(in, lenbuffer, 0, 4);
+               IO.readFully(in, lineBuffer, 0, 4);
                try {
-                       final int len = RawParseUtils.parseHexInt16(lenbuffer, 0);
+                       final int len = RawParseUtils.parseHexInt16(lineBuffer, 0);
                        if (len != 0 && len < 4)
                                throw new ArrayIndexOutOfBoundsException();
                        return len;
                } catch (ArrayIndexOutOfBoundsException err) {
                        throw new IOException("Invalid packet line header: "
-                                       + (char) lenbuffer[0] + (char) lenbuffer[1]
-                                       + (char) lenbuffer[2] + (char) lenbuffer[3]);
+                                       + (char) lineBuffer[0] + (char) lineBuffer[1]
+                                       + (char) lineBuffer[2] + (char) lineBuffer[3]);
                }
        }
 }