From 7e362277b93bbf4d59fd80485f3fe534a3ed8bba Mon Sep 17 00:00:00 2001
From: Trustin Lee <t@motd.kr>
Date: Tue, 22 Jul 2014 13:28:02 -0700
Subject: [PATCH] Reduce the default initial capacity of ChannelOutboundBuffer

Motivation:

ChannelOutboundBuffer is basically a circular array queue of its entry
objects.  Once an entry is created in the array, it is never nulled out
to reduce the allocation cost.

However, because it is a circular queue, the array almost always ends up
with as many entry instances as the size of the array, regardless of the
number of pending writes.

At worst case, a channel might have only 1 pending writes at maximum
while creating 32 entry objects, where 32 is the initial capacity of the
array.

Modifications:

- Reduce the initial capacity of the circular array queue to 4.
- Make the initial capacity of the circular array queue configurable

Result:

We spend 4 times less memory for entry objects under certain
circumstances.
---
 .../java/io/netty/channel/ChannelOutboundBuffer.java   | 10 +++++++++-
 .../socket/nio/NioSocketChannelOutboundBufferTest.java |  6 +++---
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java b/transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java
index 06cd3a3f50..6c1139cc6b 100644
--- a/transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java
+++ b/transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java
@@ -27,6 +27,7 @@ import io.netty.util.Recycler;
 import io.netty.util.Recycler.Handle;
 import io.netty.util.ReferenceCountUtil;
 import io.netty.util.internal.PlatformDependent;
+import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -42,7 +43,14 @@ public class ChannelOutboundBuffer {
 
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(ChannelOutboundBuffer.class);
 
-    protected static final int INITIAL_CAPACITY = 32;
+    protected static final int INITIAL_CAPACITY =
+            SystemPropertyUtil.getInt("io.netty.outboundBufferInitialCapacity", 4);
+
+    static {
+        if (logger.isDebugEnabled()) {
+            logger.debug("-Dio.netty.outboundBufferInitialCapacity: {}", INITIAL_CAPACITY);
+        }
+    }
 
     private static final Recycler<ChannelOutboundBuffer> RECYCLER = new Recycler<ChannelOutboundBuffer>() {
         @Override
diff --git a/transport/src/test/java/io/netty/channel/socket/nio/NioSocketChannelOutboundBufferTest.java b/transport/src/test/java/io/netty/channel/socket/nio/NioSocketChannelOutboundBufferTest.java
index 7f825d4b0e..d42100ceb6 100644
--- a/transport/src/test/java/io/netty/channel/socket/nio/NioSocketChannelOutboundBufferTest.java
+++ b/transport/src/test/java/io/netty/channel/socket/nio/NioSocketChannelOutboundBufferTest.java
@@ -36,7 +36,7 @@ public class NioSocketChannelOutboundBufferTest {
         NioSocketChannelOutboundBuffer buffer = NioSocketChannelOutboundBuffer.newInstance(channel);
         assertEquals(0, buffer.nioBufferCount());
         ByteBuffer[] buffers = buffer.nioBuffers();
-        assertEquals(32, buffers.length);
+        assertNotNull(buffers);
         for (ByteBuffer b: buffers) {
             assertNull(b);
         }
@@ -50,7 +50,7 @@ public class NioSocketChannelOutboundBufferTest {
         NioSocketChannelOutboundBuffer buffer = NioSocketChannelOutboundBuffer.newInstance(channel);
         assertEquals(0, buffer.nioBufferCount());
         ByteBuffer[] buffers = buffer.nioBuffers();
-        assertEquals(32, buffers.length);
+        assertNotNull(buffers);
         for (ByteBuffer b: buffers) {
             assertNull(b);
         }
@@ -66,7 +66,7 @@ public class NioSocketChannelOutboundBufferTest {
         }
         buffer.addFlush();
         buffers = buffer.nioBuffers();
-        assertEquals(32, buffers.length);
+        assertNotNull(buffers);
         assertEquals("Should still be 0 as not flushed yet", 1, buffer.nioBufferCount());
         for (int i = 0;  i < buffers.length; i++) {
             if (i == 0) {