Store reference to IovArray in the EpollEventLoop to reduce thread local access.

Motivation:

If we have a lot of writes going on we currently need to lookup the IovArray for each Channel that does writes. This can have quite some perf overhead. We should not need to do this and just store a reference of the IovArray on the EpollEventLoop itself.

Modifications:

- Remove IoArrayThreadLocal
- Store the IoArray in the EventLoop itself

Result:

Less FastThreadLocal lookups

transport-native-epoll/src/main/java/io/netty/channel/epoll/AbstractEpollStreamChannel.java

@@ -464,7 +464,9 @@ public abstract class AbstractEpollStreamChannel extends AbstractEpollChannel {
     private boolean doWriteMultiple(ChannelOutboundBuffer in, int writeSpinCount) throws Exception {
         if (PlatformDependent.hasUnsafe()) {
             // this means we can cast to IovArray and write the IovArray directly.
-            IovArray array = IovArrayThreadLocal.get(in);
+            IovArray array = ((EpollEventLoop) eventLoop()).cleanArray();
+            in.forEachFlushedMessage(array);
+
             int cnt = array.count();
             if (cnt >= 1) {
                 // TODO: Handle the case where cnt == 1 specially.

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollDatagramChannel.java

@@ -381,7 +381,8 @@ public final class EpollDatagramChannel extends AbstractEpollChannel implements
             writtenBytes = fd().sendToAddress(memoryAddress, data.readerIndex(), data.writerIndex(),
                     remoteAddress.getAddress(), remoteAddress.getPort());
         } else if (data instanceof CompositeByteBuf) {
-            IovArray array = IovArrayThreadLocal.get((CompositeByteBuf) data);
+            IovArray array = ((EpollEventLoop) eventLoop()).cleanArray();
+            array.add(data);
             int cnt = array.count();
             assert cnt != 0;
 

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java

@@ -54,6 +54,7 @@ final class EpollEventLoop extends SingleThreadEventLoop {
     private final IntObjectMap<AbstractEpollChannel> channels = new IntObjectHashMap<AbstractEpollChannel>(4096);
     private final boolean allowGrowing;
     private final EpollEventArray events;
+    private final IovArray iovArray = new IovArray();
 
     @SuppressWarnings("unused")
     private volatile int wakenUp;
@@ -100,6 +101,14 @@ final class EpollEventLoop extends SingleThreadEventLoop {
         }
     }
 
+    /**
+     * Return a cleared {@link IovArray} that can be used for writes in this {@link EventLoop}.
+     */
+    IovArray cleanArray() {
+        iovArray.clear();
+        return iovArray;
+    }
+
     @Override
     protected void wakeup(boolean inEventLoop) {
         if (!inEventLoop && WAKEN_UP_UPDATER.compareAndSet(this, 0, 1)) {
@@ -375,6 +384,7 @@ final class EpollEventLoop extends SingleThreadEventLoop {
             }
         } finally {
             // release native memory
+            iovArray.release();
             events.free();
         }
     }

transport-native-epoll/src/main/java/io/netty/channel/epoll/IovArrayThreadLocal.java

@@ -1,61 +0,0 @@
-/*
- * Copyright 2014 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.channel.epoll;
-
-import io.netty.buffer.CompositeByteBuf;
-import io.netty.channel.ChannelOutboundBuffer;
-import io.netty.util.concurrent.FastThreadLocal;
-
-/**
- * Allow to obtain {@link IovArray} instances.
- */
-final class IovArrayThreadLocal {
-
-    private static final FastThreadLocal<IovArray> ARRAY = new FastThreadLocal<IovArray>() {
-        @Override
-        protected IovArray initialValue() throws Exception {
-            return new IovArray();
-        }
-
-        @Override
-        protected void onRemoval(IovArray value) throws Exception {
-            // free the direct memory now
-            value.release();
-        }
-    };
-
-    /**
-     * Returns a {@link IovArray} which is filled with the flushed messages of {@link ChannelOutboundBuffer}.
-     */
-    static IovArray get(ChannelOutboundBuffer buffer) throws Exception {
-        IovArray array = ARRAY.get();
-        array.clear();
-        buffer.forEachFlushedMessage(array);
-        return array;
-    }
-
-    /**
-     * Returns a {@link IovArray} which is filled with the {@link CompositeByteBuf}.
-     */
-    static IovArray get(CompositeByteBuf buf) throws Exception {
-        IovArray array = ARRAY.get();
-        array.clear();
-        array.add(buf);
-        return array;
-    }
-
-    private IovArrayThreadLocal() { }
-}