公司需要使用java技术栈接入一套自定义的通讯协议，所以参考下dubbo的实现原理。
consumer
主要使用ThreadlessExecutor实现全consumer的全双工通讯。consumer创建本次请求的requestId用于将response和request匹配。
然后分以下几步完成一次请求发送并接收结果：
槽：发送消息前将用于接收结果的executor放到一个map中存储
发送消息：调用netty发送
挂起线程：等待response
异步接收结果：netty线程接收到结果后唤醒之前挂起的线程
槽
创造一个ThreadlessExecutor，并将其存储到DefaultFuture.FUTURES中。之后消息返回后会从DefaultFuture.FUTURES取出ThrealessExecutor并设置结果。
构建ThreadlessExecutor
<init>:56, ThreadlessExecutor (org.apache.dubbo.common.threadpool)
getCallbackExecutor:190, AbstractInvoker (org.apache.dubbo.rpc.protocol)
doInvoke:103, DubboInvoker (org.apache.dubbo.rpc.protocol.dubbo)
invoke:163, AbstractInvoker (org.apache.dubbo.rpc.protocol)
invoke:52, AsyncToSyncInvoker (org.apache.dubbo.rpc.protocol)
invoke:89, MonitorFilter (org.apache.dubbo.monitor.support)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:51, FutureFilter (org.apache.dubbo.rpc.protocol.dubbo.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:69, ConsumerContextFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:78, ListenerInvokerWrapper (org.apache.dubbo.rpc.listener)
invoke:56, InvokerWrapper (org.apache.dubbo.rpc.protocol)
doInvoke:82, FailoverClusterInvoker (org.apache.dubbo.rpc.cluster.support)
invoke:259, AbstractClusterInvoker (org.apache.dubbo.rpc.cluster.support)
intercept:47, ClusterInterceptor (org.apache.dubbo.rpc.cluster.interceptor)
invoke:92, AbstractCluster$InterceptorInvokerNode (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:82, MockClusterInvoker (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:74, InvokerInvocationHandler (org.apache.dubbo.rpc.proxy)
sayHello:-1, proxy0 (org.apache.dubbo.common.bytecode)
main:43, Consumer (org.apache.dubbo.samples.mock)
存储到DefaultFuture.FUTURES
<init>:85, DefaultFuture (org.apache.dubbo.remoting.exchange.support)
newFuture:108, DefaultFuture (org.apache.dubbo.remoting.exchange.support)
request:133, HeaderExchangeChannel (org.apache.dubbo.remoting.exchange.support.header)
request:95, HeaderExchangeClient (org.apache.dubbo.remoting.exchange.support.header)
request:91, ReferenceCountExchangeClient (org.apache.dubbo.rpc.protocol.dubbo)
doInvoke:105, DubboInvoker (org.apache.dubbo.rpc.protocol.dubbo)
invoke:163, AbstractInvoker (org.apache.dubbo.rpc.protocol)
invoke:52, AsyncToSyncInvoker (org.apache.dubbo.rpc.protocol)
invoke:89, MonitorFilter (org.apache.dubbo.monitor.support)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:51, FutureFilter (org.apache.dubbo.rpc.protocol.dubbo.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:69, ConsumerContextFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:78, ListenerInvokerWrapper (org.apache.dubbo.rpc.listener)
invoke:56, InvokerWrapper (org.apache.dubbo.rpc.protocol)
doInvoke:82, FailoverClusterInvoker (org.apache.dubbo.rpc.cluster.support)
invoke:259, AbstractClusterInvoker (org.apache.dubbo.rpc.cluster.support)
intercept:47, ClusterInterceptor (org.apache.dubbo.rpc.cluster.interceptor)
invoke:92, AbstractCluster$InterceptorInvokerNode (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:82, MockClusterInvoker (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:74, InvokerInvocationHandler (org.apache.dubbo.rpc.proxy)
sayHello:-1, proxy0 (org.apache.dubbo.common.bytecode)
main:43, Consumer (org.apache.dubbo.samples.mock)
发送消息
业务线程会将消息发送到NioEventLoop的任务队列中
offerTask:330, SingleThreadEventExecutor (io.netty.util.concurrent)
addTask:321, SingleThreadEventExecutor (io.netty.util.concurrent)
execute:765, SingleThreadEventExecutor (io.netty.util.concurrent)
safeExecute:1007, AbstractChannelHandlerContext (io.netty.channel)
write:825, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:794, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:831, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:1071, DefaultChannelPipeline (io.netty.channel)
writeAndFlush:300, AbstractChannel (io.netty.channel)
send:162, NettyChannel (org.apache.dubbo.remoting.transport.netty4)
send:178, AbstractClient (org.apache.dubbo.remoting.transport)
send:53, AbstractPeer (org.apache.dubbo.remoting.transport)
request:135, HeaderExchangeChannel (org.apache.dubbo.remoting.exchange.support.header)
request:95, HeaderExchangeClient (org.apache.dubbo.remoting.exchange.support.header)
request:91, ReferenceCountExchangeClient (org.apache.dubbo.rpc.protocol.dubbo)
doInvoke:105, DubboInvoker (org.apache.dubbo.rpc.protocol.dubbo)
invoke:163, AbstractInvoker (org.apache.dubbo.rpc.protocol)
invoke:52, AsyncToSyncInvoker (org.apache.dubbo.rpc.protocol)
invoke:89, MonitorFilter (org.apache.dubbo.monitor.support)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:51, FutureFilter (org.apache.dubbo.rpc.protocol.dubbo.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:69, ConsumerContextFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:78, ListenerInvokerWrapper (org.apache.dubbo.rpc.listener)
invoke:56, InvokerWrapper (org.apache.dubbo.rpc.protocol)
doInvoke:82, FailoverClusterInvoker (org.apache.dubbo.rpc.cluster.support)
invoke:259, AbstractClusterInvoker (org.apache.dubbo.rpc.cluster.support)
intercept:47, ClusterInterceptor (org.apache.dubbo.rpc.cluster.interceptor)
invoke:92, AbstractCluster$InterceptorInvokerNode (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:82, MockClusterInvoker (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:74, InvokerInvocationHandler (org.apache.dubbo.rpc.proxy)
sayHello:-1, proxy0 (org.apache.dubbo.common.bytecode)
main:43, Consumer (org.apache.dubbo.samples.mock)
挂起线程
waitAndDrain:89, ThreadlessExecutor (org.apache.dubbo.common.threadpool)
get:179, AsyncRpcResult (org.apache.dubbo.rpc)
invoke:61, AsyncToSyncInvoker (org.apache.dubbo.rpc.protocol)
invoke:89, MonitorFilter (org.apache.dubbo.monitor.support)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:51, FutureFilter (org.apache.dubbo.rpc.protocol.dubbo.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:69, ConsumerContextFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:78, ListenerInvokerWrapper (org.apache.dubbo.rpc.listener)
invoke:56, InvokerWrapper (org.apache.dubbo.rpc.protocol)
doInvoke:82, FailoverClusterInvoker (org.apache.dubbo.rpc.cluster.support)
invoke:259, AbstractClusterInvoker (org.apache.dubbo.rpc.cluster.support)
intercept:47, ClusterInterceptor (org.apache.dubbo.rpc.cluster.interceptor)
invoke:92, AbstractCluster$InterceptorInvokerNode (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:82, MockClusterInvoker (org.apache.dubbo.rpc.cluster.support.wrapper)
invoke:74, InvokerInvocationHandler (org.apache.dubbo.rpc.proxy)
sayHello:-1, proxy0 (org.apache.dubbo.common.bytecode)
main:43, Consumer (org.apache.dubbo.samples.mock)
异步接收结果
netty线程中接收结果并唤醒之前阻塞的业务线程
execute:138, ThreadlessExecutor (org.apache.dubbo.common.threadpool)
received:62, AllChannelHandler (org.apache.dubbo.remoting.transport.dispatcher.all)
received:90, HeartbeatHandler (org.apache.dubbo.remoting.exchange.support.header)
received:43, MultiMessageHandler (org.apache.dubbo.remoting.transport)
received:147, AbstractPeer (org.apache.dubbo.remoting.transport)
channelRead:83, NettyClientHandler (org.apache.dubbo.remoting.transport.netty4)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
channelRead:286, IdleStateHandler (io.netty.handler.timeout)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:310, ByteToMessageDecoder (io.netty.handler.codec)
channelRead:284, ByteToMessageDecoder (io.netty.handler.codec)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
channelRead:1434, DefaultChannelPipeline$HeadContext (io.netty.channel)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:965, DefaultChannelPipeline (io.netty.channel)
read:163, AbstractNioByteChannel$NioByteUnsafe (io.netty.channel.nio)
processSelectedKey:647, NioEventLoop (io.netty.channel.nio)
processSelectedKeysOptimized:582, NioEventLoop (io.netty.channel.nio)
processSelectedKeys:499, NioEventLoop (io.netty.channel.nio)
run:461, NioEventLoop (io.netty.channel.nio)
run:884, SingleThreadEventExecutor$5 (io.netty.util.concurrent)
run:30, FastThreadLocalRunnable (io.netty.util.concurrent)
run:748, Thread (java.lang)
provider
接收请求：netty线程接收请求
切换线程：将请求转给业务线程
返回结果：业务线程处理之后调用channel.write返回结果
接收请求
received:62, AllChannelHandler (org.apache.dubbo.remoting.transport.dispatcher.all)
received:90, HeartbeatHandler (org.apache.dubbo.remoting.exchange.support.header)
received:43, MultiMessageHandler (org.apache.dubbo.remoting.transport)
received:147, AbstractPeer (org.apache.dubbo.remoting.transport)
channelRead:98, NettyServerHandler (org.apache.dubbo.remoting.transport.netty4)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
channelRead:286, IdleStateHandler (io.netty.handler.timeout)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:310, ByteToMessageDecoder (io.netty.handler.codec)
channelRead:284, ByteToMessageDecoder (io.netty.handler.codec)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
channelRead:1434, DefaultChannelPipeline$HeadContext (io.netty.channel)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:965, DefaultChannelPipeline (io.netty.channel)
read:163, AbstractNioByteChannel$NioByteUnsafe (io.netty.channel.nio)
processSelectedKey:647, NioEventLoop (io.netty.channel.nio)
processSelectedKeysOptimized:582, NioEventLoop (io.netty.channel.nio)
processSelectedKeys:499, NioEventLoop (io.netty.channel.nio)
run:461, NioEventLoop (io.netty.channel.nio)
run:884, SingleThreadEventExecutor$5 (io.netty.util.concurrent)
run:30, FastThreadLocalRunnable (io.netty.util.concurrent)
run:748, Thread (java.lang)
切换线程
sayHello:31, DemoServiceImpl (org.apache.dubbo.samples.mock.impl)
invokeMethod:-1, Wrapper1 (org.apache.dubbo.common.bytecode)
doInvoke:47, JavassistProxyFactory$1 (org.apache.dubbo.rpc.proxy.javassist)
invoke:84, AbstractProxyInvoker (org.apache.dubbo.rpc.proxy)
invoke:56, DelegateProviderMetaDataInvoker (org.apache.dubbo.config.invoker)
invoke:56, InvokerWrapper (org.apache.dubbo.rpc.protocol)
invoke:52, ExceptionFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:89, MonitorFilter (org.apache.dubbo.monitor.support)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:46, TimeoutFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:77, TraceFilter (org.apache.dubbo.rpc.protocol.dubbo.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:129, ContextFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:152, GenericFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:38, ClassLoaderFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
invoke:41, EchoFilter (org.apache.dubbo.rpc.filter)
invoke:81, ProtocolFilterWrapper$1 (org.apache.dubbo.rpc.protocol)
reply:145, DubboProtocol$1 (org.apache.dubbo.rpc.protocol.dubbo)
handleRequest:100, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)
received:175, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)
received:51, DecodeHandler (org.apache.dubbo.remoting.transport)
run:57, ChannelEventRunnable (org.apache.dubbo.remoting.transport.dispatcher)
runWorker:1149, ThreadPoolExecutor (java.util.concurrent)
run:624, ThreadPoolExecutor$Worker (java.util.concurrent)
run:748, Thread (java.lang)
返回结果
offerTask:327, SingleThreadEventExecutor (io.netty.util.concurrent)
addTask:321, SingleThreadEventExecutor (io.netty.util.concurrent)
execute:765, SingleThreadEventExecutor (io.netty.util.concurrent)
safeExecute:1007, AbstractChannelHandlerContext (io.netty.channel)
write:825, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:794, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:831, AbstractChannelHandlerContext (io.netty.channel)
writeAndFlush:1071, DefaultChannelPipeline (io.netty.channel)
writeAndFlush:300, AbstractChannel (io.netty.channel)
send:162, NettyChannel (org.apache.dubbo.remoting.transport.netty4)
send:98, HeaderExchangeChannel (org.apache.dubbo.remoting.exchange.support.header)
send:87, HeaderExchangeChannel (org.apache.dubbo.remoting.exchange.support.header)
lambda$handleRequest$0:110, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)
accept:-1, 195186633 (org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeHandler$$Lambda$148)
uniWhenComplete:774, CompletableFuture (java.util.concurrent)
uniWhenCompleteStage:792, CompletableFuture (java.util.concurrent)
whenComplete:2153, CompletableFuture (java.util.concurrent)
whenComplete:110, CompletableFuture (java.util.concurrent)
handleRequest:101, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)
received:175, HeaderExchangeHandler (org.apache.dubbo.remoting.exchange.support.header)
received:51, DecodeHandler (org.apache.dubbo.remoting.transport)
run:57, ChannelEventRunnable (org.apache.dubbo.remoting.transport.dispatcher)
runWorker:1149, ThreadPoolExecutor (java.util.concurrent)
run:624, ThreadPoolExecutor$Worker (java.util.concurrent)
run:748, Thread (java.lang)
细节
getPreferredExecutorService
不论consumer还是provider，都是通过AllChannelHandler#received接收远程信息。区别在于consumer使用的是ThreadlessExecutor，而provider使用的是ThreadPoolExecutor。
AllChannelHandler#received中调用的getPreferredExecutorService方法会根据接收的消息是否为response来决定使用哪个线程。
| ThreadlessExecutor | ThreadPoolExecutor | |
|---|---|---|
| 用途 | consumer接收 | provider接收 |
| 初始化时机 | 发送请求前 | 接收请求 |
| 存储位置 | DefaultFuture.FUTURES | DefaultExecutorRepository.data |
| 存储key | requestId | 端口 |
| 业务线程？ | 业务线程&IO线程 | 业务线程 |
ThreadlessExecutor#execute由IO线程调用，ThreadlessExecutor#waitAndDrain由业务线程调用
ThreadPoolExecutor存储位置相关细节可以看DefaultExecutorRepository#createExecutorIfAbsent
requestId是标识每次请求的唯一id，每构造一次Request实例都会由Request#newId生成一个新的
ThreadlessExecutor
ThreadlessExecutor中并没有启动新的线程，其主要作用是将异步的远程访问转为同步。所以在调用堆栈中可以看到AsyncToSyncInvoker。
业务线程调用waitAndDrain时，若远程provider尚未返回数据，queue.take()会使线程挂起。
netty线程接收到provider的返回值之后会调用ThreadlessExecutor#excute，将结果添加到queue中。于是之前因queue.take()挂起的线程可以继续运行了。
AllChannelHandler
调试的过程中发现，AllChannelHandler#received方法比较关键，consumer和provider的接收功能都会在此方法中从io线程转换到业务线程
于是想研究下AllChannelHandler，主要从以下几个方面研究：
实例化：一般情况下，一个实例要么在需要的时候被实例化，要么在需要之前实例化并存到一个地方。所以想知道AllChannelHandler的实例属于哪一种，如果是后者那么它存到哪里了？
调用：基于上面的问题，如果是后一种情况，如何从存的地方拿出来并使用的？
维度：每个provider都有一个AllChannelHandler实例？还是每个端口一个实例？
实例化
AllChannelHandler作为nettyServerHandler的一个属性存储
截图为provider，consumer原理与provider大体一致
调用
远程消息到来后，会进入nettyServerHandler#channelRead方法中，此方法会调用AllChannelHandler#received方法
截图为provider，consumer原理与provider大体一致
维度
AllChannelHandler的创建维度是ip:port，若多个provider在同一个ip:port开启，也只会创建一个AllChannelHandler（换句话说就只创建一个netty服务端）。多个consumer从同一个ip:port消费不同的服务，也只会创建一个。
对于provider，DubboProtocol#openServer中会根据ip:port缓存netty服务端，避免重复创建。而AllChannelHandler的创建又与netty服务端的创建相对应，所以AllChannelHandler的维度也是ip:port
对于consumer，DubboProtocol#getSharedClient中会根据ip:port缓存netty客户端
