From e40c27d9ed1678207c1ca4554e70ed5e2534d93f Mon Sep 17 00:00:00 2001
From: Jakob Buchgraber <buchgr@google.com>
Date: Fri, 3 Apr 2015 10:51:29 -0700
Subject: [PATCH] Avoid object allocations for HTTP2 child streams.

Motivation:

We are allocating a hash map for every HTTP2 Stream to store it's children.
Most streams are leafs in the priority tree and don't have children.

Modification:

 - Only allocate children when we actually use them.
 - Make EmptyIntObjectMap not throw a UnsupportedOperationException on remove, but return null instead (as is stated in it's javadoc).

Result:

Fewer unnecessary allocations.
---
 .../codec/http2/DefaultHttp2Connection.java    | 18 ++++++++++++------
 .../util/collection/PrimitiveCollections.java  |  2 +-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java b/codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java
index e798ef3979..c99c87aeed 100644
--- a/codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java
+++ b/codec-http2/src/main/java/io/netty/handler/codec/http2/DefaultHttp2Connection.java
@@ -38,6 +38,7 @@ import io.netty.buffer.ByteBuf;
 import io.netty.handler.codec.http2.Http2StreamRemovalPolicy.Action;
 import io.netty.util.collection.IntObjectHashMap;
 import io.netty.util.collection.IntObjectMap;
+import io.netty.util.collection.PrimitiveCollections;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -216,7 +217,7 @@ public class DefaultHttp2Connection implements Http2Connection {
         private State state = IDLE;
         private short weight = DEFAULT_PRIORITY_WEIGHT;
         private DefaultStream parent;
-        private IntObjectMap<DefaultStream> children = newChildMap();
+        private IntObjectMap<DefaultStream> children = PrimitiveCollections.emptyIntObjectMap();
         private int totalChildWeights;
         private int prioritizableForTree = 1;
         private boolean resetSent;
@@ -503,6 +504,12 @@ public class DefaultHttp2Connection implements Http2Connection {
             }
         }
 
+        private void initChildrenIfEmpty() {
+            if (children == PrimitiveCollections.<DefaultStream>emptyIntObjectMap()) {
+                children = new IntObjectHashMap<DefaultStream>(4);
+            }
+        }
+
         @Override
         public final boolean remoteSideOpen() {
             return state == HALF_CLOSED_LOCAL || state == OPEN || state == RESERVED_REMOTE;
@@ -539,7 +546,7 @@ public class DefaultHttp2Connection implements Http2Connection {
             totalChildWeights = 0;
             prioritizableForTree = isPrioritizable() ? 1 : 0;
             IntObjectMap<DefaultStream> prevChildren = children;
-            children = newChildMap();
+            children = PrimitiveCollections.emptyIntObjectMap();
             return prevChildren;
         }
 
@@ -561,6 +568,9 @@ public class DefaultHttp2Connection implements Http2Connection {
                 }
             }
 
+            // Lazily initialize the children to save object allocations.
+            initChildrenIfEmpty();
+
             if (children.put(child.id(), child) == null) {
                 totalChildWeights += child.weight();
                 incrementPrioritizableForTree(child.prioritizableForTree(), oldParent);
@@ -673,10 +683,6 @@ public class DefaultHttp2Connection implements Http2Connection {
         }
     }
 
-    private static IntObjectMap<DefaultStream> newChildMap() {
-        return new IntObjectHashMap<DefaultStream>(4);
-    }
-
     /**
      * Allows a correlation to be made between a stream and its old parent before a parent change occurs
      */
diff --git a/common/src/main/java/io/netty/util/collection/PrimitiveCollections.java b/common/src/main/java/io/netty/util/collection/PrimitiveCollections.java
index fcb7077ae5..9903070883 100644
--- a/common/src/main/java/io/netty/util/collection/PrimitiveCollections.java
+++ b/common/src/main/java/io/netty/util/collection/PrimitiveCollections.java
@@ -68,7 +68,7 @@ public final class PrimitiveCollections {
 
         @Override
         public Object remove(int key) {
-            throw new UnsupportedOperationException("remove");
+            return null;
         }
 
         @Override