Use FastThreadLocal for CodecOutputList

Motivation:

We used Recycler for the CodecOutputList which is not optimized for the use-case of access only from the same Thread all the time.

Modifications:

- Use FastThreadLocal for CodecOutputList
- Add benchmark

Result:

Less overhead in our codecs.

codec/src/main/java/io/netty/handler/codec/CodecOutputList.java

@@ -15,7 +15,8 @@
  */
 package io.netty.handler.codec;
 
-import io.netty.util.Recycler;
+import io.netty.util.concurrent.FastThreadLocal;
+import io.netty.util.internal.MathUtil;
 
 import java.util.AbstractList;
 import java.util.RandomAccess;
@@ -27,25 +28,81 @@ import static io.netty.util.internal.ObjectUtil.checkNotNull;
  */
 final class CodecOutputList extends AbstractList<Object> implements RandomAccess {
 
-    private static final Recycler<CodecOutputList> RECYCLER = new Recycler<CodecOutputList>() {
+    private static final CodecOutputListRecycler NOOP_RECYCLER = new CodecOutputListRecycler() {
+
         @Override
-        protected CodecOutputList newObject(Handle handle) {
-            return new CodecOutputList(handle);
+        public void recycle(CodecOutputList object) {
+            // drop on the floor and let the GC handle it.
         }
     };
 
-    static CodecOutputList newInstance() {
-        return RECYCLER.get();
+    private static final FastThreadLocal<CodecOutputLists> CODEC_OUTPUT_LISTS_POOL =
+            new FastThreadLocal<CodecOutputLists>() {
+                @Override
+                protected CodecOutputLists initialValue() throws Exception {
+                    // 16 CodecOutputList per Thread are cached.
+                    return new CodecOutputLists(16);
+                }
+            };
+
+    private interface CodecOutputListRecycler {
+        void recycle(CodecOutputList codecOutputList);
     }
 
-    private final Recycler.Handle handle;
+    private static final class CodecOutputLists implements CodecOutputListRecycler {
+        private final CodecOutputList[] elements;
+        private final int mask;
+
+        private int currentIdx;
+        private int count;
+
+        CodecOutputLists(int numElements) {
+            elements = new CodecOutputList[MathUtil.safeFindNextPositivePowerOfTwo(numElements)];
+            for (int i = 0; i < elements.length; ++i) {
+                // Size of 16 should be good enough for the majority of all users as an initial capacity.
+                elements[i] = new CodecOutputList(this, 16);
+            }
+            count = elements.length;
+            currentIdx = elements.length;
+            mask = elements.length - 1;
+        }
+
+        public CodecOutputList getOrCreate() {
+            if (count == 0) {
+                // Return a new CodecOutputList which will not be cached. We use a size of 4 to keep the overhead
+                // low.
+                return new CodecOutputList(NOOP_RECYCLER, 4);
+            }
+            --count;
+
+            int idx = (currentIdx - 1) & mask;
+            CodecOutputList list = elements[idx];
+            currentIdx = idx;
+            return list;
+        }
+
+        @Override
+        public void recycle(CodecOutputList codecOutputList) {
+            int idx = currentIdx;
+            elements[idx] = codecOutputList;
+            currentIdx = (idx + 1) & mask;
+            ++count;
+            assert count <= elements.length;
+        }
+    }
+
+    static CodecOutputList newInstance() {
+        return CODEC_OUTPUT_LISTS_POOL.get().getOrCreate();
+    }
+
+    private final CodecOutputListRecycler recycler;
     private int size;
-    // Size of 16 should be good enough for 99 % of all users.
-    private Object[] array = new Object[16];
+    private Object[] array;
     private boolean insertSinceRecycled;
 
-    private CodecOutputList(Recycler.Handle handle) {
-        this.handle = handle;
+    private CodecOutputList(CodecOutputListRecycler recycler, int size) {
+        this.recycler = recycler;
+        array = new Object[size];
     }
 
     @Override
@@ -135,9 +192,10 @@ final class CodecOutputList extends AbstractList<Object> implements RandomAccess
         for (int i = 0 ; i < size; i ++) {
             array[i] = null;
         }
-        clear();
+        size = 0;
         insertSinceRecycled = false;
-        RECYCLER.recycle(this, handle);
+
+        recycler.recycle(this);
     }
 
     /**

microbench/src/main/java/io/netty/handler/codec/AdvancedCodecOutputListBenchmark.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2017 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.handler.codec;
+
+import io.netty.microbench.util.AbstractMicrobenchmark;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Threads;
+
+@State(Scope.Benchmark)
+@Threads(16)
+public class AdvancedCodecOutputListBenchmark extends AbstractMicrobenchmark {
+
+    private static final Object ELEMENT = new Object();
+
+    @Param({ "1", "4" })
+    public int elements;
+
+    @Benchmark
+    public boolean codecOutListAllocRecycle() {
+        return benchmark(elements, CodecOutputList.newInstance(), CodecOutputList.newInstance(),
+                CodecOutputList.newInstance(), CodecOutputList.newInstance());
+    }
+
+    private static boolean benchmark(int elements, CodecOutputList list1, CodecOutputList list2,
+                                     CodecOutputList list3, CodecOutputList list4) {
+        return (benchmark(elements, list1) == benchmark(elements, list2)) ==
+                (benchmark(elements, list3) == benchmark(elements, list4));
+    }
+
+    private static boolean benchmark(int elements, CodecOutputList list) {
+        for (int i = 0; i < elements; ++i) {
+            list.add(ELEMENT);
+        }
+        list.recycle();
+        return list.insertSinceRecycled();
+    }
+}