Channel体系分析
接口与类结构体系
-- [I]AttributeMap, ChannelOutboundInvoker, Comparable -- [I]AttributeMap
---- [I]Channel ---- [C]DefaultAttributeMap
-- [I]Channel, [C]DefaultAttributeMap
---- [AC]AbstractChannel
------ [AC]AbstractNioChannel
-------- [AC]AbstractNioMessageChannel, [AC]AbstractNioByteChannel
-- [I]Channel -- [I]Channel
---- [I]ServerChannel ---- [I]DuplexChannel
------ [I](N)ServerSocketChannel ------ [I](N)SocketChannel
-- [I](N)ServerSocketChannel, [AC]AbstractNioMessageChannel -- (N)SocketChannel, AbstractNioByteChannel
---- [C]NioServerSocketChannel ---- [C]NioSocketChannelAbstractChannel新增加的特性
- EventLoop与该Channel是否兼容
- 获取本地绑定的SocketAddress
- 获取远程连接到的SocketAddress
- doxxxx接口，注册，绑定，连接，关闭，去注册，开始读，写等实现的接口特性约定。Epoll，kqueue上会用到。
AbstractChannel实现的逻辑
- 构造初始化逻辑，包括id创建，unsafe创建，pipeline创建
- 是否可写，是否已经注册，
- 不可写之前还有多少byte数据要写出
- 在可写之前有多少byte数据待写出
- pipeline，parent字段落地
- 获取的ByteBufAllocator，EventLoop，pipeline，parent，unsafe，closeFuture等实例
- 本地地址，远程地址的获取。支持cache，不是每次都获取
- bind，connect，disconnect，close，deregister，flush，read，write，writeAndFlush，newPromise，voidPromise，newSucceededFuture，newFailedFuture。都是触发pipeline的相应方法。
- 重写hashcode，直接返回id的hashCode
- 重写equals，在这里认为==的才算equals。
- 重写compare，就是拿id进行compare
- 重写toString
AbstractNioChannel实现的逻辑
- 落地JDK的SelectableChannel， SelectionKey实例，以及暴露对外获取接口
- 落地readInterestOp字段
- 落地connectPromise ChannelPromise字段
- 落地connectTimeoutFuture ScheduledFuture字段
- 落地远端地址字段SocketAddress requestedRemoteAddress
- 对外暴露NioUnsafe，NioEventLoop等实例获取接口
- 对外暴露是否开启，是否读挂起等判断接口
- 设置读挂起，清理读挂起逻辑实现
- EventLoop与该Channel是否兼容的逻辑实现。就是看EventLoop是不是NioEventLoop
- 注册、去注册操作实现。
- 开始读操作实现
- 关闭操作实现
- newDirectBuffer逻辑实现。这个行为不在接口约定中。
注册操作实现
这个实现还是蛮严格的：
protected void doRegister() throws Exception {
boolean selected = false;
for (;;) {
try {
selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
return;
} catch (CancelledKeyException e) {
if (!selected) {
// Force the Selector to select now as the "canceled" SelectionKey may still be
// cached and not removed because no Select.select(..) operation was called yet.
eventLoop().selectNow();
selected = true;
} else {
// We forced a select operation on the selector before but the SelectionKey is still cached
// for whatever reason. JDK bug ?
throw e;
}
}
}
}注册这个事情看起来不复杂，但是要严格写好写对就要注意。
注册本来只需要用：
/**
* Registers this channel with the given selector, returning a selection
* key.
*
* <p> If this channel is currently registered with the given selector then
* the selection key representing that registration is returned. The key's
* interest set will have been changed to <tt>ops</tt>, as if by invoking
* the {@link SelectionKey#interestOps(int) interestOps(int)} method. If
* the <tt>att</tt> argument is not <tt>null</tt> then the key's attachment
* will have been set to that value. A {@link CancelledKeyException} will
* be thrown if the key has already been cancelled.
*
* <p> Otherwise this channel has not yet been registered with the given
* selector, so it is registered and the resulting new key is returned.
* The key's initial interest set will be <tt>ops</tt> and its attachment
* will be <tt>att</tt>.
*
* <p> This method may be invoked at any time. If this method is invoked
* while another invocation of this method or of the {@link
* #configureBlocking(boolean) configureBlocking} method is in progress
* then it will first block until the other operation is complete. This
* method will then synchronize on the selector's key set and therefore may
* block if invoked concurrently with another registration or selection
* operation involving the same selector. </p>
*
* <p> If this channel is closed while this operation is in progress then
* the key returned by this method will have been cancelled and will
* therefore be invalid. </p>
*
* @param sel
* The selector with which this channel is to be registered
*
* @param ops
* The interest set for the resulting key
*
* @param att
* The attachment for the resulting key; may be <tt>null</tt>
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws ClosedSelectorException
* If the selector is closed
*
* @throws IllegalBlockingModeException
* If this channel is in blocking mode
*
* @throws IllegalSelectorException
* If this channel was not created by the same provider
* as the given selector
*
* @throws CancelledKeyException
* If this channel is currently registered with the given selector
* but the corresponding key has already been cancelled
*
* @throws IllegalArgumentException
* If a bit in the <tt>ops</tt> set does not correspond to an
* operation that is supported by this channel, that is, if
* {@code set & ~validOps() != 0}
*
* @return A key representing the registration of this channel with
* the given selector
*/
java.nio.channels.SelectableChannel.register(Selector sel, int ops, Object att)
throws ClosedChannelException;Selector实例，用的是EventLoop的unwrappedSelector实例
int ops 此处目前注册时送的是0(可以送定义的4个之外的？)，SelectionKey定义了4个：
- OP_READ 1
- OP_WRITE 4
- OP_CONNECT 8
- OP_ACCEPT 16
Object att 表示要塞给Selector实例的附件，此处送的是AbstractNioChannel
doRegister异常的处理：
- 如果是CancelledKeyException之外的异常，直接抛出，中断注册动作。比如：IllegalSelectorException，IllegalBlockingModeException，ClosedChannelException，ClosedSelectorException等异常。
- 如果是CancelledKeyException异常，尝试操作eventLoop().selectNow();注意这个时候用的EventLoop的selector字段。 注意：EventLoop中unwrappedSelector 与 selector两个字段的区别。做完eventLoop().selectNow()之后再尝试注册，如果还是CancelledKeyException异常则对外抛出异常。selectNow()的目的是规避有些SelectionKey处于Cancel状态但还在缓存中，调用selectNow可以尝试将其remove。
整个流程图示如下：
+
|
+----------v----------+
+-----------------------> SelectableChannel |
| | .register |
| +----------+----------+
| |
| |
| +----------v----------+ +-----------------+
| | is success +---Y---> return |
| +---------------------+ +-----------------+
| N N
| | |
| +------------------v-----+ +---v----------------+
| | CancelledKeyException | | other exception |
| +-----------+------------+ +------+-------------+
| | |
| | | +-----------------+
| +--------v--------+ +-------> throw exp |
| | selected? | +-------^---------+
| +-------------+---+ |
| N | |
| | +--------Y--------------------------+
| +---------v---+
| | selectNow |
+----+ selected. |
+-------------+
有几个注意点
- 在注册时若有CancelledKeyException需要做一次selectNow，然后再重试注册，否则可能会触发JDK bug。Selectkey被cancel了，但是仍在缓存中。
- 针对1的情况，也会有做了selectNow后再重试注册后还会有CancelledKeyException，那么此时直接抛出异常就好了。
JDK SelectionKey定义的4个操作没有0，但是注册时ops时为啥送0 ？可以参见io.netty.channel.socket.nio.AbstractNioChannel doRegister() ？？ #1836，有netty作者，和写这个代码的commiter的解释。大致意思就是为了解决潜在的JDK的bug。
It's an intentional stuff(有意设计) to deal with a potential（潜在的） JDK bug where it returns a selection key with readyOps set to 0 for no good reason, leading to a spin loop. So, I'd leave it as it is.
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead to a spin loop
有个dengyuankai272同学说到如下，感觉解释的更靠谱，作者解释的那个0不是注册的这个地方
There are two way to register interested events:
Channel.register()
SelectionKey.interestOps(int)
netty use 2.
After binding channel to selector with interestOps 0, netty will invoke fireChannelActive()
->fire a read event
->HeadContext.unsafe.doBeginRead()
->SelectionKey.interestOps(int)
to set interestOps.去除注册操作逻辑实现
用了eventLoop().cancel(selectionKey());
跟进去逻辑如下：
+-------------------+
| SelectionKey |
| .cancel |
+--------+----------+
|
|
+--------v----------+
| cancelledKey add 1|
+--------+----------+
|
|
|
+----------v-----------+
| cancelledKeys |
+----+ >= CLEANUP_INTERVAL+----+
| | (256,hard-code) | |
N +----------------------+ Y
| |
| |
+-----v--------+ +-------------v-------+
| return | | needsToSelectAgain|
| | | = true |
+--------------+ +-----------+---------+
|
| // poll task,processSelectedKeysPlain,closeAll等地方触发
+-----------v---------+
| selector |
| .selectNow |
+---------------------+
开始读操作逻辑实现
+------------------+
| SelectionKey +----N------+
| .isValid | |
+------------------+ +------v------+
Y | return |
| +-------------+
+--------v---------+
| readPending |
| = true |
+--------+---------+
|
|
|
|
+-----------------v----------------+
| selectionKey.interestOps |
| (interestOps | readInterestOp) |
+--------------+-------------------+
关闭操作逻辑实现
connectPromise.tryFailure(DO_CLOSE_CLOSED_CHANNEL_EXCEPTION);
connectTimeoutFuture.cancel(false);
将连接的promise和连接超时的future设置成失败和取消。
newDirectBuffer操作逻辑实现
是将非direct的bug包装转换成direct的buf，比如PooledHeapByteBuf就不是direct的。
分配direct buf，一是靠ByteBufAllocator.directBuffer，另一是靠ByteBufUtil.threadLocalDirectBuffer()。
这个还是有点意思的，还会涉及到 ReferenceCountUtil，待分析。
newDirectBuffer会用在AbstractNioByteChannel.filterOutboundMessage(Object)逻辑中。
AbstractNioMessageChannel实现的逻辑
NioMessageUnsafe.read实现的逻辑
在RestExpress项目中，这个方法的实际调用栈示例与简单分析如下：
ServerBootstrapFactory$2.newThread(Runnable) line: 90 // 开始创建worker线程
ThreadPerTaskExecutor.execute(Runnable) line: 33
NioEventLoop(SingleThreadEventExecutor).doStartThread() line: 894
NioEventLoop(SingleThreadEventExecutor).startThread() line: 865
NioEventLoop(SingleThreadEventExecutor).execute(Runnable) line: 758
NioSocketChannel$NioSocketChannelUnsafe(AbstractChannel$AbstractUnsafe).register(EventLoop, ChannelPromise) line: 483
NioEventLoop(SingleThreadEventLoop).register(ChannelPromise) line: 80
NioEventLoop(SingleThreadEventLoop).register(Channel) line: 74 // return register(new DefaultChannelPromise(channel, this)); 拿Channel new了一个DefaultChannelPromise，这个Channel对象就是上面boss线程read出来message Object，也就是NioSocketChannel实例。
NioEventLoopGroup(MultithreadEventLoopGroup).register(Channel) line: 86
ServerBootstrap$ServerBootstrapAcceptor.channelRead(ChannelHandlerContext, Object) line: 255 // 这个是boss线程accept之后准备投递到worker线程的地方 childGroup.register(child).addListener(new ChannelFutureListener() {...
DefaultChannelHandlerContext(AbstractChannelHandlerContext).invokeChannelRead(Object) line: 362
AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext, Object) line: 348
DefaultChannelPipeline$HeadContext(AbstractChannelHandlerContext).fireChannelRead(Object) line: 340
DefaultChannelPipeline$HeadContext.channelRead(ChannelHandlerContext, Object) line: 1408
DefaultChannelPipeline$HeadContext(AbstractChannelHandlerContext).invokeChannelRead(Object) line: 362
AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext, Object) line: 348
DefaultChannelPipeline.fireChannelRead(Object) line: 930
AbstractNioMessageChannel$NioMessageUnsafe.read() line: 93 // ** 正在分析的这个方法
NioEventLoop.processSelectedKey(SelectionKey, AbstractNioChannel) line: 677 // 是accept或者read事件 或者是0 触发boss线程上的read动作。注意是 boss线程。在boss线程上accept等同于read。 if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) { unsafe.read(); }
NioEventLoop.processSelectedKeysOptimized() line: 612
NioEventLoop.processSelectedKeys() line: 529
NioEventLoop.run() line: 491
SingleThreadEventExecutor$5.run() line: 905
Thread.run() line: 748 这个堆栈实际上也解释了，boss线程从接到IO上的accept事件到交给work线程去做后续的读取的整个过程。
更详细的用sql查trace数据：
select * from trace_data where id>=15309 and THREAD_ID=13 and STACK_NUM>5 order by id逻辑流程：
靠子类的doReadMessages将需要读取的message读取出来放到readBuf (一个List)
迭代读取到的message挨个通知pipeline channelRead事件，pipeline.fireChannelRead
清理readBuf
通知pipeline channelReadComplete事件，pipeline.fireChannelReadComplete
如果异常则关闭 closeOnReadError 并通知pipeline fireExceptionCaught事件
子类实现
此处我们用到的AbstractNioMessageChannel 有个子类实现是NioServerSocketChannel
doReadMessages实先的内容是： 做accept操作 并创建NioSocketChannel实例作为read到的message，这个Channel实例看上面的的调用栈，会在NioEventLoop(SingleThreadEventLoop).register(Channel) line: 74用到。
AbstractNioByteChannel实现的逻辑
看下trace数据：
select * from trace_data where class_name like '%AbstractNioByteChannel%'数据：
ID THREAD_ID STACK_NUM THREAD_NAME METHOD_ID CLASS_NAME METHOD_NAME LINE_NUM
15336 13 7 boss-0 14143 io/netty/channel/nio/AbstractNioByteChannel <clinit> 45
15350 13 8 boss-0 14123 io/netty/channel/nio/AbstractNioByteChannel <init> 67
15374 13 15 boss-0 14144 io/netty/channel/nio/AbstractNioByteChannel$NioByteUnsafe <init> 97
15407 13 9 boss-0 14186 io/netty/channel/nio/AbstractNioByteChannel$1 <init> 49
15420 13 13 boss-0 14127 io/netty/channel/nio/AbstractNioByteChannel metadata 85
20790 15 5 worker-0 14147 io/netty/channel/nio/AbstractNioByteChannel$NioByteUnsafe read 186
20793 15 6 worker-0 14128 io/netty/channel/nio/AbstractNioByteChannel shouldBreakReadReady 89
26019 15 30 worker-0 14133 io/netty/channel/nio/AbstractNioByteChannel filterOutboundMessage 283
26288 15 30 worker-0 14139 io/netty/channel/nio/AbstractNioByteChannel clearOpWrite 348
26357 15 5 worker-0 14147 io/netty/channel/nio/AbstractNioByteChannel$NioByteUnsafe read 186
26360 15 6 worker-0 14128 io/netty/channel/nio/AbstractNioByteChannel shouldBreakReadReady 89
26757 15 6 worker-0 14145 io/netty/channel/nio/AbstractNioByteChannel$NioByteUnsafe closeOnRead 111
26767 15 7 worker-0 14141 io/netty/channel/nio/AbstractNioByteChannel access$000 43
26768 15 8 worker-0 14129 io/netty/channel/nio/AbstractNioByteChannel isAllowHalfClosure 93创建是在boss线程，工作是在work线程，主要用到的方法是read。
NioByteUnsafe.read实现的逻辑
tarce 数据中的记录：
ID THREAD_ID STACK_NUM THREAD_NAME METHOD_ID CLASS_NAME METHOD_NAME LINE_NUM
20790 15 5 worker-0 14147 io/netty/channel/nio/AbstractNioByteChannel$NioByteUnsafe read 186从NioByteUnsafe.read到http object解码的调用栈：
HttpRequestDecoder(HttpObjectDecoder).decode(ChannelHandlerContext, ByteBuf, List<Object>) line: 196
HttpRequestDecoder(ByteToMessageDecoder).decodeRemovalReentryProtection(ChannelHandlerContext, ByteBuf, List<Object>) line: 502
HttpRequestDecoder(ByteToMessageDecoder).callDecode(ChannelHandlerContext, ByteBuf, List<Object>) line: 441
HttpRequestDecoder(ByteToMessageDecoder).channelRead(ChannelHandlerContext, Object) line: 278
DefaultChannelHandlerContext(AbstractChannelHandlerContext).invokeChannelRead(Object) line: 362
AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext, Object) line: 348
DefaultChannelHandlerContext(AbstractChannelHandlerContext).fireChannelRead(Object) line: 340
ReadTimeoutHandler(IdleStateHandler).channelRead(ChannelHandlerContext, Object) line: 286
DefaultChannelHandlerContext(AbstractChannelHandlerContext).invokeChannelRead(Object) line: 362
AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext, Object) line: 348
DefaultChannelPipeline$HeadContext(AbstractChannelHandlerContext).fireChannelRead(Object) line: 340
DefaultChannelPipeline$HeadContext.channelRead(ChannelHandlerContext, Object) line: 1408
DefaultChannelPipeline$HeadContext(AbstractChannelHandlerContext).invokeChannelRead(Object) line: 362
AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext, Object) line: 348
DefaultChannelPipeline.fireChannelRead(Object) line: 930
NioSocketChannel$NioSocketChannelUnsafe(AbstractNioByteChannel$NioByteUnsafe).read() line: 163
NioEventLoop.processSelectedKey(SelectionKey, AbstractNioChannel) line: 677
NioEventLoop.processSelectedKeysOptimized() line: 612
NioEventLoop.processSelectedKeys() line: 529
NioEventLoop.run() line: 491
SingleThreadEventExecutor$5.run() line: 905
Thread.run() line: 748 逻辑实现：
shouldBreakReadReady检查， 判断是否应该中断 读ready的处理，针对的情况可以参见其代码判断逻辑
调用子类实现的doReadBytes方法，读取byte的动作
流水线触发读事件 pipeline.fireChannelRead，fireChannelRead接受的参数是Object类型...，所以此处给的ByteBuf和上面NioMessageUnsafe read时给送Channel都可以的。
流水线触发读完成事件 pipeline.fireChannelReadComplete()
DefaultChannelHandlerContext 这个等到后面Handler相关分析的地方再继续分析
AbstractNioByteChannel.filterOutboundMessage逻辑实现
- msg是ByteBuf类型的，若不是Direct的buf，则用newDirectBuffer wrap一下
- msg如果是FileRegion类型的，原样返回
- 不是1和2两种类型的，抛出UnsupportedOperationException异常
AbstractNioByteChannel.clearOpWrite逻辑实现
nio的select()的时候，只要数据通道允许写，每次select()返回的OP_WRITE都是true。所以在nio的写数据里面，我们在每次需要写数据之前把数据放到缓冲区，并且注册OP_WRITE，对selector进行wakeup()，这样这一轮select()发现有OP_WRITE之后，将缓冲区数据写入channel，清空缓冲区，并且反注册OP_WRITE，写数据完成。
protected final void clearOpWrite() {
final SelectionKey key = selectionKey();
// Check first if the key is still valid as it may be canceled as part of the deregistration
// from the EventLoop
// See https://github.com/netty/netty/issues/2104
if (!key.isValid()) {
return;
}
final int interestOps = key.interestOps();
if ((interestOps & SelectionKey.OP_WRITE) != 0) {
key.interestOps(interestOps & ~SelectionKey.OP_WRITE); // 反注册？？
}
}NioServerSocketChannel分析
构造函数指定这个类感兴趣的I/O事件是OP_ACCEPT
doBind实现
这个类实现了doBind具体细节
对于不同的JDK版本用了不同的bind方法
JDK7以上(含) java.nio.channels.ServerSocketChannel.bind(SocketAddress, int)
JDK7以下 java.net.ServerSocket.bind(SocketAddress, int)
@Override
protected void doBind(SocketAddress localAddress) throws Exception {
if (PlatformDependent.javaVersion() >= 7) {
javaChannel().bind(localAddress, config.getBacklog());
} else {
javaChannel().socket().bind(localAddress, config.getBacklog());
}
}doClose实现
直接调用ServerSocketChannel的close方法，没有额外逻辑。
doReadMessages实现
用NIO的ServerSocketChannel实例accept出NIO的SocketChannel实例，再用NIO的SocketChannel实例创建了netty对应的NioSocketChannel实例，并将此实例作为message返回到上下文处理逻辑中。（为了整个封装，messgae不一定指消息报文，此处就是指从ServerSocketChannel-->SocketChannel-->NioSocketChannel）
NioSocketChannel创建实例初始化时又做了很大一堆逻辑处理。
connect相关实现
NioServerSocketChannel端不支持doConnect操作，不支持doFinishConnect操作，不支持doDisconnect操作，不支持doWriteMessage操作，不支持filterOutboundMessage操作。
遗留问题
AbstractNioUnsafe的实现逻辑，诸如connect等
io.netty.channel.nio.AbstractNioMessageChannel.doWrite(ChannelOutboundBuffer)实现逻辑待分析，在rest server这个项目中并没有用到这个逻辑。
ServerSocketChannel 这个类1.4就有了，但是它的bind方法在1.7才提供，详细参见其注释。但是JDK1.7为啥要新增这个方法呢？为了解决啥问题？// TODO