A new ChannelHandler that allows the user to control the flow of messages if upstream handlers emit more than one event for each read()
Motivation: Some handlers such as HttpObjectDecoder can emit more than one event per read() which leads to problems in downstream handlers that expect only one event and hope that ChannelConfig#setAutoRead(false) prevents further events being sent while they're processing the one they've just received. Modifications: A new handler called FlowControlHandler that feeds off read() and isAutoRead() and acts as a holding buffer if auto reading gets turned off and more events arrive while auto reading is off. Result: Fixes issues such as #4895.
This commit is contained in:
Roger Kapsi
Scott Mitchell
parent
04e33fd2d8
commit
5eb0127c2a
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/*
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* Copyright 2016 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License, version
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* 2.0 (the "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations under
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* the License.
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*/
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package io.netty.handler.flow;
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import java.util.ArrayDeque;
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import java.util.Queue;
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import io.netty.channel.Channel;
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import io.netty.channel.ChannelConfig;
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import io.netty.channel.ChannelDuplexHandler;
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import io.netty.channel.ChannelHandler;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.channel.ChannelInboundHandlerAdapter;
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import io.netty.channel.ChannelPipeline;
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import io.netty.handler.codec.ByteToMessageDecoder;
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import io.netty.handler.codec.MessageToByteEncoder;
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import io.netty.util.Recycler;
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import io.netty.util.Recycler.Handle;
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import io.netty.util.ReferenceCountUtil;
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import io.netty.util.internal.logging.InternalLogger;
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import io.netty.util.internal.logging.InternalLoggerFactory;
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/**
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* The {@link FlowControlHandler} ensures that only one message per {@code read()} is sent downstream.
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*
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* Classes such as {@link ByteToMessageDecoder} or {@link MessageToByteEncoder} are free to emit as
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* many events as they like for any given input. A channel's auto reading configuration doesn't usually
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* apply in these scenarios. This is causing problems in downstream {@link ChannelHandler}s that would
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* like to hold subsequent events while they're processing one event. It's a common problem with the
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* {@code HttpObjectDecoder} that will very often fire a {@code HttpRequest} that is immediately followed
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* by a {@code LastHttpContent} event.
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*
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* <pre>
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* {@link ChannelPipeline} pipeline = ...;
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*
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* pipeline.addLast(new HttpServerCodec());
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* pipeline.addLast(new {@link FlowControlHandler}());
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*
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* pipeline.addLast(new MyExampleHandler());
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*
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* class MyExampleHandler extends {@link ChannelInboundHandlerAdapter} {
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* @Override
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* public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
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* if (msg instanceof HttpRequest) {
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* ctx.channel().config().setAutoRead(false);
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*
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* // The FlowControlHandler will hold any subsequent events that
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* // were emitted by HttpObjectDecoder until auto reading is turned
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* // back on or Channel#read() is being called.
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* }
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* }
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* }
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* </pre>
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*
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* @see ChannelConfig#setAutoRead(boolean)
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*/
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public class FlowControlHandler extends ChannelDuplexHandler {
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private static final InternalLogger logger = InternalLoggerFactory.getInstance(FlowControlHandler.class);
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private final boolean releaseMessages;
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private RecyclableArrayDeque queue;
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private ChannelConfig config;
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private boolean shouldConsume;
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public FlowControlHandler() {
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this(true);
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}
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public FlowControlHandler(boolean releaseMessages) {
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this.releaseMessages = releaseMessages;
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}
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/**
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* Returns a copy of the underlying {@link Queue}. This method exists for
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* testing, debugging and inspection purposes and it is not Thread safe!
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*/
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Queue<Object> queue() {
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RecyclableArrayDeque queue = this.queue;
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if (queue == null) {
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return new ArrayDeque<Object>(0);
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}
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return new ArrayDeque<Object>(queue);
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}
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/**
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* Releases all messages and destroys the {@link Queue}.
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*/
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private void destroy() {
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if (queue != null) {
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if (!queue.isEmpty()) {
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logger.trace("Non-empty queue: {}", queue);
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if (releaseMessages) {
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Object msg;
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while ((msg = queue.poll()) != null) {
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ReferenceCountUtil.safeRelease(msg);
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}
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}
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}
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queue.recycle();
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queue = null;
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}
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}
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@Override
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public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
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config = ctx.channel().config();
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}
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@Override
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public void channelInactive(ChannelHandlerContext ctx) throws Exception {
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destroy();
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ctx.fireChannelInactive();
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}
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@Override
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public void read(ChannelHandlerContext ctx) throws Exception {
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if (dequeue(ctx, 1) == 0) {
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// It seems no messages were consumed. We need to read() some
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// messages from upstream and once one arrives it need to be
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// relayed to downstream to keep the flow going.
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shouldConsume = true;
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ctx.read();
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}
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}
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@Override
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public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
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if (queue == null) {
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queue = RecyclableArrayDeque.newInstance();
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}
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queue.offer(msg);
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// We just received one message. Do we need to relay it regardless
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// of the auto reading configuration? The answer is yes if this
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// method was called as a result of a prior read() call.
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int minConsume = shouldConsume ? 1 : 0;
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shouldConsume = false;
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dequeue(ctx, minConsume);
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}
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@Override
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public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
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// Don't relay completion events from upstream as they
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// make no sense in this context. See dequeue() where
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// a new set of completion events is being produced.
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}
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/**
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* Dequeues one or many (or none) messages depending on the channel's auto
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* reading state and returns the number of messages that were consumed from
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* the internal queue.
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*
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* The {@code minConsume} argument is used to force {@code dequeue()} into
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* consuming that number of messages regardless of the channel's auto
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* reading configuration.
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*
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* @see #read(ChannelHandlerContext)
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* @see #channelRead(ChannelHandlerContext, Object)
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*/
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private int dequeue(ChannelHandlerContext ctx, int minConsume) {
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if (queue != null) {
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int consumed = 0;
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Object msg;
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while ((consumed < minConsume) || config.isAutoRead()) {
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msg = queue.poll();
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if (msg == null) {
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break;
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}
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++consumed;
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ctx.fireChannelRead(msg);
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}
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// We're firing a completion event every time one (or more)
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// messages were consumed and the queue ended up being drained
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// to an empty state.
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if (queue.isEmpty() && consumed > 0) {
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ctx.fireChannelReadComplete();
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}
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return consumed;
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}
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return 0;
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}
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/**
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* A recyclable {@link ArrayDeque}.
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*/
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private static final class RecyclableArrayDeque extends ArrayDeque<Object> {
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private static final long serialVersionUID = 0L;
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/**
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* A value of {@code 2} should be a good choice for most scenarios.
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*/
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private static final int DEFAULT_NUM_ELEMENTS = 2;
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private static final Recycler<RecyclableArrayDeque> RECYCLER = new Recycler<RecyclableArrayDeque>() {
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@Override
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protected RecyclableArrayDeque newObject(Handle<RecyclableArrayDeque> handle) {
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return new RecyclableArrayDeque(DEFAULT_NUM_ELEMENTS, handle);
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}
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};
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public static RecyclableArrayDeque newInstance() {
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return RECYCLER.get();
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}
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private final Handle<RecyclableArrayDeque> handle;
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private RecyclableArrayDeque(int numElements, Handle<RecyclableArrayDeque> handle) {
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super(numElements);
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this.handle = handle;
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}
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public void recycle() {
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clear();
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handle.recycle(this);
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}
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}
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}
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/*
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* Copyright 2016 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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/**
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* Package to control the flow of messages.
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*/
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package io.netty.handler.flow;
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@ -0,0 +1,389 @@
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/*
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* Copyright 2016 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License, version
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* 2.0 (the "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations under
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* the License.
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*/
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package io.netty.handler.flow;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertFalse;
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import static org.junit.Assert.assertThat;
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import static org.junit.Assert.assertTrue;
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import static org.junit.Assert.fail;
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import java.net.SocketAddress;
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import java.util.List;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.Exchanger;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicInteger;
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import java.util.concurrent.atomic.AtomicReference;
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import org.hamcrest.collection.IsIterableContainingInOrder;
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import org.junit.AfterClass;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import io.netty.bootstrap.Bootstrap;
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import io.netty.bootstrap.ServerBootstrap;
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import io.netty.buffer.ByteBuf;
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import io.netty.buffer.Unpooled;
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import io.netty.channel.Channel;
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import io.netty.channel.ChannelConfig;
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import io.netty.channel.ChannelDuplexHandler;
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import io.netty.channel.ChannelHandler;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.channel.ChannelInboundHandlerAdapter;
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import io.netty.channel.ChannelInitializer;
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import io.netty.channel.ChannelOption;
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import io.netty.channel.ChannelPipeline;
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import io.netty.channel.EventLoopGroup;
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import io.netty.channel.nio.NioEventLoopGroup;
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import io.netty.channel.socket.nio.NioServerSocketChannel;
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import io.netty.channel.socket.nio.NioSocketChannel;
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import io.netty.handler.codec.ByteToMessageDecoder;
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import io.netty.util.ReferenceCountUtil;
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public class FlowControlHandlerTest {
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private static EventLoopGroup GROUP;
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@BeforeClass
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public static void init() {
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GROUP = new NioEventLoopGroup();
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}
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@AfterClass
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public static void destroy() {
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GROUP.shutdownGracefully();
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}
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/**
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* The {@link OneByteToThreeStringsDecoder} decodes this {@code byte[]} into three messages.
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*/
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private static ByteBuf newOneMessage() {
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return Unpooled.wrappedBuffer(new byte[]{ 1 });
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}
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private static Channel newServer(final boolean autoRead, final ChannelHandler... handlers) {
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assertTrue(handlers.length >= 1);
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ServerBootstrap serverBootstrap = new ServerBootstrap();
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serverBootstrap.group(GROUP)
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.channel(NioServerSocketChannel.class)
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.childOption(ChannelOption.AUTO_READ, autoRead)
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.childHandler(new ChannelInitializer<Channel>() {
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@Override
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protected void initChannel(Channel ch) throws Exception {
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ChannelPipeline pipeline = ch.pipeline();
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pipeline.addLast(new OneByteToThreeStringsDecoder());
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pipeline.addLast(handlers);
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}
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});
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return serverBootstrap.bind(0)
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.syncUninterruptibly()
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.channel();
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}
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private static Channel newClient(SocketAddress server) {
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Bootstrap bootstrap = new Bootstrap();
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bootstrap.group(GROUP)
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.channel(NioSocketChannel.class)
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.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 1000)
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.handler(new ChannelInboundHandlerAdapter() {
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@Override
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public void channelRead(ChannelHandlerContext ctx, Object msg) {
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fail("In this test the client is never receiving a message from the server.");
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}
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});
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return bootstrap.connect(server)
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.syncUninterruptibly()
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.channel();
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}
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/**
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* This test demonstrates the default behavior if auto reading
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* is turned on from the get-go and you're trying to turn it off
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* once you've received your first message.
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*
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* NOTE: This test waits for the client to disconnect which is
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* interpreted as the signal that all {@code byte}s have been
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* transferred to the server.
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*/
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@Test
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public void testAutoReadingOn() throws Exception {
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final CountDownLatch latch = new CountDownLatch(3);
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ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
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@Override
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public void channelRead(ChannelHandlerContext ctx, Object msg) {
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ReferenceCountUtil.release(msg);
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// We're turning off auto reading in the hope that no
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// new messages are being sent but that is not true.
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ctx.channel().config().setAutoRead(false);
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latch.countDown();
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}
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};
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Channel server = newServer(true, handler);
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Channel client = newClient(server.localAddress());
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try {
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client.writeAndFlush(newOneMessage())
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.syncUninterruptibly();
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// We received three messages even through auto reading
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// was turned off after we received the first message.
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assertTrue(latch.await(1L, TimeUnit.SECONDS));
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} finally {
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client.close();
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server.close();
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}
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}
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/**
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* This test demonstrates the default behavior if auto reading
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* is turned off from the get-go and you're calling read() in
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* the hope that only one message will be returned.
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*
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* NOTE: This test waits for the client to disconnect which is
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* interpreted as the signal that all {@code byte}s have been
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* transferred to the server.
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*/
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@Test
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public void testAutoReadingOff() throws Exception {
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final Exchanger<Channel> peerRef = new Exchanger<Channel>();
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final CountDownLatch latch = new CountDownLatch(3);
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ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
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@Override
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public void channelActive(ChannelHandlerContext ctx) throws Exception {
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peerRef.exchange(ctx.channel(), 1L, TimeUnit.SECONDS);
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ctx.fireChannelActive();
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}
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@Override
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public void channelRead(ChannelHandlerContext ctx, Object msg) {
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ReferenceCountUtil.release(msg);
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latch.countDown();
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}
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};
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Channel server = newServer(false, handler);
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Channel client = newClient(server.localAddress());
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try {
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// The client connection on the server side
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Channel peer = peerRef.exchange(null, 1L, TimeUnit.SECONDS);
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// Write the message
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client.writeAndFlush(newOneMessage())
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.syncUninterruptibly();
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// Read the message
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peer.read();
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// We received all three messages but hoped that only one
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// message was read because auto reading was off and we
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// invoked the read() method only once.
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assertTrue(latch.await(1L, TimeUnit.SECONDS));
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} finally {
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client.close();
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server.close();
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}
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}
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/**
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* The {@link FlowControlHandler} will simply pass-through all messages
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* if auto reading is on and remains on.
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*/
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@Test
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public void testFlowAutoReadOn() throws Exception {
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final CountDownLatch latch = new CountDownLatch(3);
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ChannelInboundHandlerAdapter handler = new ChannelDuplexHandler() {
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@Override
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public void channelRead(ChannelHandlerContext ctx, Object msg) {
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latch.countDown();
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}
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};
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FlowControlHandler flow = new FlowControlHandler();
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Channel server = newServer(true, flow, handler);
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Channel client = newClient(server.localAddress());
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try {
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// Write the message
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client.writeAndFlush(newOneMessage())
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.syncUninterruptibly();
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// We should receive 3 messages
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assertTrue(latch.await(1L, TimeUnit.SECONDS));
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assertTrue(flow.queue().isEmpty());
|
||||
} finally {
|
||||
client.close();
|
||||
server.close();
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* The {@link FlowControlHandler} will pass down messages one by one
|
||||
* if {@link ChannelConfig#setAutoRead(boolean)} is being toggled.
|
||||
*/
|
||||
@Test
|
||||
public void testFlowToggleAutoRead() throws Exception {
|
||||
final Exchanger<Channel> peerRef = new Exchanger<Channel>();
|
||||
final AtomicReference<CountDownLatch> latchRef
|
||||
= new AtomicReference<CountDownLatch>(new CountDownLatch(1));
|
||||
|
||||
final AtomicInteger counter = new AtomicInteger();
|
||||
|
||||
ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
|
||||
@Override
|
||||
public void channelActive(ChannelHandlerContext ctx) throws Exception {
|
||||
peerRef.exchange(ctx.channel(), 1L, TimeUnit.SECONDS);
|
||||
ctx.fireChannelActive();
|
||||
}
|
||||
|
||||
@Override
|
||||
public void channelRead(ChannelHandlerContext ctx, Object msg) {
|
||||
ReferenceCountUtil.release(msg);
|
||||
|
||||
// Disable auto reading after each message
|
||||
counter.incrementAndGet();
|
||||
ctx.channel().config().setAutoRead(false);
|
||||
|
||||
CountDownLatch latch = latchRef.get();
|
||||
latch.countDown();
|
||||
}
|
||||
};
|
||||
|
||||
FlowControlHandler flow = new FlowControlHandler();
|
||||
Channel server = newServer(true, flow, handler);
|
||||
Channel client = newClient(server.localAddress());
|
||||
try {
|
||||
// The client connection on the server side
|
||||
Channel peer = peerRef.exchange(null, 1L, TimeUnit.SECONDS);
|
||||
|
||||
client.writeAndFlush(newOneMessage())
|
||||
.syncUninterruptibly();
|
||||
|
||||
// channelRead(1)
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertFalse(peer.config().isAutoRead());
|
||||
assertEquals(1, counter.get());
|
||||
assertThat(flow.queue(), IsIterableContainingInOrder.<Object>contains("2", "3"));
|
||||
|
||||
// channelRead(2)
|
||||
latchRef.set(new CountDownLatch(1));
|
||||
peer.config().setAutoRead(true);
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertFalse(peer.config().isAutoRead());
|
||||
assertEquals(2, counter.get());
|
||||
assertThat(flow.queue(), IsIterableContainingInOrder.<Object>contains("3"));
|
||||
|
||||
// channelRead(3)
|
||||
latchRef.set(new CountDownLatch(1));
|
||||
peer.config().setAutoRead(true);
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertFalse(peer.config().isAutoRead());
|
||||
assertEquals(3, counter.get());
|
||||
assertTrue(flow.queue().isEmpty());
|
||||
} finally {
|
||||
client.close();
|
||||
server.close();
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* The {@link FlowControlHandler} will pass down messages one by one
|
||||
* if auto reading is off and the user is calling {@code read()} on
|
||||
* their own.
|
||||
*/
|
||||
@Test
|
||||
public void testFlowAutoReadOff() throws Exception {
|
||||
final Exchanger<Channel> peerRef = new Exchanger<Channel>();
|
||||
final AtomicReference<CountDownLatch> latchRef
|
||||
= new AtomicReference<CountDownLatch>(new CountDownLatch(1));
|
||||
final AtomicInteger counter = new AtomicInteger();
|
||||
|
||||
ChannelInboundHandlerAdapter handler = new ChannelDuplexHandler() {
|
||||
@Override
|
||||
public void channelActive(ChannelHandlerContext ctx) throws Exception {
|
||||
peerRef.exchange(ctx.channel(), 1L, TimeUnit.SECONDS);
|
||||
ctx.fireChannelActive();
|
||||
}
|
||||
|
||||
@Override
|
||||
public void channelRead(ChannelHandlerContext ctx, Object msg) {
|
||||
counter.incrementAndGet();
|
||||
|
||||
CountDownLatch latch = latchRef.get();
|
||||
latch.countDown();
|
||||
}
|
||||
};
|
||||
|
||||
FlowControlHandler flow = new FlowControlHandler();
|
||||
Channel server = newServer(false, flow, handler);
|
||||
Channel client = newClient(server.localAddress());
|
||||
try {
|
||||
// The client connection on the server side
|
||||
Channel peer = peerRef.exchange(null, 1L, TimeUnit.SECONDS);
|
||||
|
||||
// Write the message
|
||||
client.writeAndFlush(newOneMessage())
|
||||
.syncUninterruptibly();
|
||||
|
||||
// channelRead(1)
|
||||
peer.read();
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertEquals(1, counter.get());
|
||||
assertThat(flow.queue(), IsIterableContainingInOrder.<Object>contains("2", "3"));
|
||||
|
||||
// channelRead(2)
|
||||
latchRef.set(new CountDownLatch(1));
|
||||
peer.read();
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertEquals(2, counter.get());
|
||||
assertThat(flow.queue(), IsIterableContainingInOrder.<Object>contains("3"));
|
||||
|
||||
// channelRead(3)
|
||||
latchRef.set(new CountDownLatch(1));
|
||||
peer.read();
|
||||
assertTrue(latchRef.get().await(1L, TimeUnit.SECONDS));
|
||||
assertEquals(3, counter.get());
|
||||
assertTrue(flow.queue().isEmpty());
|
||||
} finally {
|
||||
client.close();
|
||||
server.close();
|
||||
}
|
||||
}
|
||||
|
||||
/**
|
||||
* This is a fictional message decoder. It decodes each {@code byte}
|
||||
* into three strings.
|
||||
*/
|
||||
private static final class OneByteToThreeStringsDecoder extends ByteToMessageDecoder {
|
||||
@Override
|
||||
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
|
||||
for (int i = 0; i < in.readableBytes(); i++) {
|
||||
out.add("1");
|
||||
out.add("2");
|
||||
out.add("3");
|
||||
}
|
||||
in.readerIndex(in.readableBytes());
|
||||
}
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user