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本文主要研究一下reactor-netty的TcpClient如何往eventLoop提交task
实例
TcpClient client = TcpClient.create("localhost",8888);
LOGGER.info("client:{}",client.getClass());
Mono<? extends NettyContext> handler = client.newHandler((inbound,outbound) -> {
return outbound.sendString(Mono.just("Hello World!")).then(inbound.receive()
.asString().next().log().then());
});
LOGGER.info("handler:{}",handler.getClass()); //NOTE reactor.core.publisher.MonoCreate
handler.subscribe();
TcpClient.newHandler
reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/tcp/TcpClient.java
protected Mono<NettyContext> newHandler(BiFunction<? super NettyInbound,? super NettyOutbound,? extends Publisher<Void>> handler,InetSocketAddress address,boolean secure,Consumer<? super Channel> onSetup) {
final BiFunction<? super NettyInbound,? extends Publisher<Void>>
targetHandler =
null == handler ? ChannelOperations.noopHandler() : handler;
return Mono.create(sink -> {
SocketAddress remote = address != null ? address : options.getAddress();
ChannelPool pool = null;
PoolResources poolResources = options.getPoolResources();
if (poolResources != null) {
pool = poolResources.selectOrCreate(remote,options,doHandler(null,sink,secure,remote,null,null),options.getLoopResources().onClient(options.preferNative()));
}
ContextHandler<SocketChannel> contextHandler =
doHandler(targetHandler,pool,onSetup);
sink.onCancel(contextHandler);
if (pool == null) {
Bootstrap b = options.get();
b.remoteAddress(remote);
b.handler(contextHandler);
contextHandler.setFuture(b.connect());
}
else {
contextHandler.setFuture(pool.acquire());
}
});
}
注意这里的pool.acquire()或者b.connect()
SimpleChannelPool.acquireHealthyFromPoolOrNew
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/pool/SimpleChannelPool.java
/**
* Tries to retrieve healthy channel from the pool if any or creates a new channel otherwise.
* @param promise the promise to provide acquire result.
* @return future for acquiring a channel.
*/
private Future<Channel> acquireHealthyFromPoolOrNew(final Promise<Channel> promise) {
try {
final Channel ch = pollChannel();
if (ch == null) {
// No Channel left in the pool bootstrap a new Channel
Bootstrap bs = bootstrap.clone();
bs.attr(POOL_KEY,this);
ChannelFuture f = connectChannel(bs);
if (f.isDone()) {
notifyConnect(f,promise);
} else {
f.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
notifyConnect(future,promise);
}
});
}
return promise;
}
EventLoop loop = ch.eventLoop();
if (loop.inEventLoop()) {
doHealthCheck(ch,promise);
} else {
loop.execute(new Runnable() {
@Override
public void run() {
doHealthCheck(ch,promise);
}
});
}
} catch (Throwable cause) {
promise.tryFailure(cause);
}
return promise;
}
/**
* Bootstrap a new {@link Channel}. The default implementation uses {@link Bootstrap#connect()},sub-classes may
* override this.
* <p>
* The {@link Bootstrap} that is passed in here is cloned via {@link Bootstrap#clone()},so it is safe to modify.
*/
protected ChannelFuture connectChannel(Bootstrap bs) {
return bs.connect();
}
pool.acquire()最后调用的是SimpleChannelPool.acquireHealthyFromPoolOrNew，它最后调用connectChannel也是调用Bootstrap.connect
Bootstrap.connect
netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/Bootstrap.java
/**
* Connect a {@link Channel} to the remote peer.
*/
public ChannelFuture connect() {
validate();
SocketAddress remoteAddress = this.remoteAddress;
if (remoteAddress == null) {
throw new IllegalStateException("remoteAddress not set");
}
return doResolveAndConnect(remoteAddress,config.localAddress());
}
/**
* @see #connect()
*/
private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress,final SocketAddress localAddress) {
final ChannelFuture regFuture = initAndRegister();
final Channel channel = regFuture.channel();
if (regFuture.isDone()) {
if (!regFuture.isSuccess()) {
return regFuture;
}
return doResolveAndConnect0(channel,remoteAddress,localAddress,channel.newPromise());
} else {
// Registration future is almost always fulfilled already,but just in case it's not.
final PendingRegistrationPromise promise = new PendingRegistrationPromise(channel);
regFuture.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
// Directly obtain the cause and do a null check so we only need one volatile read in case of a
// failure.
Throwable cause = future.cause();
if (cause != null) {
// Registration on the EventLoop Failed so fail the ChannelPromise directly to not cause an
// IllegalStateException once we try to access the EventLoop of the Channel.
promise.setFailure(cause);
} else {
// Registration was successful,so set the correct executor to use.
// See https://github.com/netty/netty/issues/2586
promise.registered();
doResolveAndConnect0(channel,promise);
}
}
});
return promise;
}
}
注意这里调用了initAndRegister
然后调用doResolveAndConnect0
initAndRegister
netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/AbstractBootstrap.java
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
channel = channelFactory.newChannel();
init(channel);
} catch (Throwable t) {
if (channel != null) {
// channel can be null if newChannel crashed (eg SocketException("too many open files"))
channel.unsafe().closeForcibly();
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(channel,GlobalEventExecutor.INSTANCE).setFailure(t);
}
// as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor
return new DefaultChannelPromise(new FailedChannel(),GlobalEventExecutor.INSTANCE).setFailure(t);
}
ChannelFuture regFuture = config().group().register(channel);
if (regFuture.cause() != null) {
if (channel.isRegistered()) {
channel.close();
} else {
channel.unsafe().closeForcibly();
}
}
// If we are here and the promise is not Failed,it's one of the following cases:
// 1) If we attempted registration from the event loop,the registration has been completed at this point.
// i.e. It's safe to attempt bind() or connect() now because the channel has been registered.
// 2) If we attempted registration from the other thread,the registration request has been successfully
// added to the event loop's task queue for later execution.
// i.e. It's safe to attempt bind() or connect() now:
// because bind() or connect() will be executed *after* the scheduled registration task is executed
// because register(),bind(),and connect() are all bound to the same thread.
return regFuture;
}
这里先调用channelFactory.newChannel()来创建一个channel，之后进行初始化，这里可能抛出SocketException("too many open files")，异常的话直接设置fail并返回DefaultChannelPromise
注意这里调用了config().group().register(channel)，在reactor-netty中这个group是MultithreadEventLoopGroup.java
io.netty.channel.ReflectiveChannelFactory.newChannel()
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/ReflectiveChannelFactory.java
public T newChannel() {
try {
return clazz.getConstructor().newInstance();
} catch (Throwable t) {
throw new ChannelException("Unable to create Channel from class " + clazz,t);
}
}
这里new的是NioSocketChannel.class
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/socket/nio/NioSocketChannel.java
private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
private static SocketChannel newSocket(SelectorProvider provider) {
try {
/**
* Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
* {@link SelectorProvider#provider()} which is called by each SocketChannel.open() otherwise.
*
* See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.
*/
return provider.openSocketChannel();
} catch (IOException e) {
throw new ChannelException("Failed to open a socket.",e);
}
}
/**
* Create a new instance using the given {@link SelectorProvider}.
*/
public NioSocketChannel(SelectorProvider provider) {
this(newSocket(provider));
}
mac操作系统这里的provider是sun.nio.ch.KQueueSelectorProvider，openSocketChannel调用的是SelectorProviderImpl的方法
jre/lib/rt.jar!/sun/nio/ch/SelectorProviderImpl.class
public SocketChannel openSocketChannel() throws IOException {
return new SocketChannelImpl(this);
}
jre/lib/rt.jar!/sun/nio/ch/SocketChannelImpl.class
SocketChannelImpl(SelectorProvider var1) throws IOException {
super(var1);
this.fd = Net.socket(true);
this.fdVal = IoUtil.fdVal(this.fd);
this.state = 0;
}
注意这里调用了Net.socket(true)，创建FileDescriptor，可能抛出SocketException("too many open files")
Bootstrap.init(channel)
netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/Bootstrap.java
void init(Channel channel) throws Exception {
ChannelPipeline p = channel.pipeline();
p.addLast(config.handler());
final Map<ChannelOption<?>,Object> options = options0();
synchronized (options) {
setChannelOptions(channel,logger);
}
final Map<AttributeKey<?>,Object> attrs = attrs0();
synchronized (attrs) {
for (Entry<AttributeKey<?>,Object> e: attrs.entrySet()) {
channel.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
}
}
}
这里主要是设置一些options和属性
MultithreadEventLoopGroup.register(channel)
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/MultithreadEventLoopGroup.java
public ChannelFuture register(Channel channel) {
return next().register(channel);
}
这里的next返回的是SingleThreadEventLoop
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/SingleThreadEventLoop.java
public ChannelFuture register(Channel channel) {
return register(new DefaultChannelPromise(channel,this));
}
public ChannelFuture register(final ChannelPromise promise) {
ObjectUtil.checkNotNull(promise,"promise");
promise.channel().unsafe().register(this,promise);
return promise;
}
这里的unsafe是AbstractChannel$AbstractUnsafe
AbstractChannel$AbstractUnsafe
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/AbstractChannel.java
public final void register(EventLoop eventLoop,final ChannelPromise promise) {
if (eventLoop == null) {
throw new NullPointerException("eventLoop");
}
if (isRegistered()) {
promise.setFailure(new IllegalStateException("registered to an event loop already"));
return;
}
if (!isCompatible(eventLoop)) {
promise.setFailure(
new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
return;
}
AbstractChannel.this.eventLoop = eventLoop;
if (eventLoop.inEventLoop()) {
register0(promise);
} else {
try {
eventLoop.execute(new Runnable() {
@Override
public void run() {
register0(promise);
}
});
} catch (Throwable t) {
logger.warn(
"Force-closing a channel whose registration task was not accepted by an event loop: {}",AbstractChannel.this,t);
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise,t);
}
}
}
这里可以看到调用eventLoop.execute，这个eventLoop是NioEventLoop，调用的是父类SingleThreadEventLoop.execute
注意这里对ChannelPromise再包装了一下，调用了register0操作
SingleThreadEventLoop.execute
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
boolean inEventLoop = inEventLoop();
if (inEventLoop) {
addTask(task);
} else {
startThread();
addTask(task);
if (isShutdown() && removeTask(task)) {
reject();
}
}
if (!addTaskWakesUp && wakesUpForTask(task)) {
wakeup(inEventLoop);
}
}
/**
* Add a task to the task queue,or throws a {@link RejectedExecutionException} if this instance was shutdown
* before.
*/
protected void addTask(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
if (!offerTask(task)) {
reject(task);
}
}
final boolean offerTask(Runnable task) {
if (isShutdown()) {
reject();
}
return taskQueue.offer(task);
}
可以看到这里execute调用的是addTask，而addTask调用offerTask，最后往taskQueue里头offer任务
register0
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/AbstractChannel.java
private void register0(ChannelPromise promise) {
try {
// check if the channel is still open as it could be closed in the mean time when the register
// call was outside of the eventLoop
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
boolean firstRegistration = neverRegistered;
doRegister();
neverRegistered = false;
registered = true;
// Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
// user may already fire events through the pipeline in the ChannelFutureListener.
pipeline.invokeHandlerAddedIfNeeded();
safeSetSuccess(promise);
pipeline.fireChannelRegistered();
// Only fire a channelActive if the channel has never been registered. This prevents firing
// multiple channel actives if the channel is deregistered and re-registered.
if (isActive()) {
if (firstRegistration) {
pipeline.fireChannelActive();
} else if (config().isAutoRead()) {
// This channel was registered before and autoRead() is set. This means we need to begin read
// again so that we process inbound data.
//
// See https://github.com/netty/netty/issues/4805
beginRead();
}
}
} catch (Throwable t) {
// Close the channel directly to avoid FD leak.
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise,t);
}
}
taskQueue取出来执行的是register0操作，主要是fireChannelRegistered以及fireChannelActive，这个方法将registered字段设置为true
netty-transport-4.1.20.Final-sources.jar!/io/netty/channel/socket/nio/NioSocketChannel.java
public boolean isActive() {
SocketChannel ch = javaChannel();
return ch.isOpen() && ch.isConnected();
}
是否active主要判断是否open，以及connected
Bootstrap.doResolveAndConnect0
netty-transport-4.1.20.Final-sources.jar!/io/netty/bootstrap/Bootstrap.java
private ChannelFuture doResolveAndConnect0(final Channel channel,SocketAddress remoteAddress,final SocketAddress localAddress,final ChannelPromise promise) {
try {
final EventLoop eventLoop = channel.eventLoop();
final AddressResolver<SocketAddress> resolver = this.resolver.getResolver(eventLoop);
if (!resolver.isSupported(remoteAddress) || resolver.isResolved(remoteAddress)) {
// Resolver has no idea about what to do with the specified remote address or it's resolved already.
doConnect(remoteAddress,promise);
return promise;
}
final Future<SocketAddress> resolveFuture = resolver.resolve(remoteAddress);
if (resolveFuture.isDone()) {
final Throwable resolveFailureCause = resolveFuture.cause();
if (resolveFailureCause != null) {
// Failed to resolve immediately
channel.close();
promise.setFailure(resolveFailureCause);
} else {
// Succeeded to resolve immediately; cached? (or did a blocking lookup)
doConnect(resolveFuture.getNow(),promise);
}
return promise;
}
// Wait until the name resolution is finished.
resolveFuture.addListener(new FutureListener<SocketAddress>() {
@Override
public void operationComplete(Future<SocketAddress> future) throws Exception {
if (future.cause() != null) {
channel.close();
promise.setFailure(future.cause());
} else {
doConnect(future.getNow(),promise);
}
}
});
} catch (Throwable cause) {
promise.tryFailure(cause);
}
return promise;
}
private static void doConnect(
final SocketAddress remoteAddress,final ChannelPromise connectPromise) {
// This method is invoked before channelRegistered() is triggered. Give user handlers a chance to set up
// the pipeline in its channelRegistered() implementation.
final Channel channel = connectPromise.channel();
channel.eventLoop().execute(new Runnable() {
@Override
public void run() {
if (localAddress == null) {
channel.connect(remoteAddress,connectPromise);
} else {
channel.connect(remoteAddress,connectPromise);
}
connectPromise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
}
});
}
这里在initAndRegister执行成功之后，会触发doResolveAndConnect0，而这里才是真正的执行connect操作
Bootstrap.connect的主要步骤
能够执行多少connect，有这么多个关卡：
- 创建和初始化channel：AbstractBootstrap的initAndRegister方法中newChannel及init()返回的ChannelFuture不是Failed的，可能因为SocketException("too many open files")无法创建FileDescriptor
- 提交注册channel的task：往eventLoop注册这个register任务，这里要求taskQueue队列能够容纳得下，默认是Integer.MAX_VALUE没有问题；容纳不下则会reject这个task，抛出RejectedExecutionException(
Force-closing a channel whose registration task was not accepted by an event loop)，则这个promise被设置为failure，initAndRegister不成功则channel则直接被close掉
taskQueue中的register0(promise)这个任务，更改状态为REGISTERED，之后触发下面这个task去connect，之后判断是否open和connect，如果是则状态变更为ACTIVE
- 注册这个register ChannelFuture的operationComplete回调：调用doResolveAndConnect0，doResolveAndConnect0执行的是channel的connect
channel的状态变化是Created->REGISTERED->CONNECT->ACTIVE
21:53:50.934 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.resources.DefaultPoolResources - Created [id: 0x1ebe331c],now 1 active connections
21:53:50.941 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.ContextHandler - After pipeline DefaultChannelPipeline{(reactor.left.loggingHandler = io.netty.handler.logging.LoggingHandler),(SimpleChannelPool$1#0 = io.netty.channel.pool.SimpleChannelPool$1),(reactor.right.reactiveBridge = reactor.ipc.netty.channel.ChannelOperationsHandler)}
21:53:50.942 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c] REGISTERED
21:54:49.561 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c] CONNECT: localhost/127.0.0.1:8888
21:54:49.571 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] ACTIVE
收发数据并关闭channel
变成active之后就会触发newHandler里头Lambda表达式往channel写数据发送
22:13:12.174 [main] DEBUG reactor.ipc.netty.channel.PooledClientContextHandler - Acquiring existing channel from pool: DefaultPromise@97e93f1(success: [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888]) SimpleChannelPool{activeConnections=1}
22:13:19.773 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.PooledClientContextHandler - Acquired active channel: [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888]
22:13:25.291 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.ChannelOperations - [Channel] [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] handler is being applied: com.example.demo.TcpTest$$Lambda$7/1541049864@41d1fa89
22:15:17.748 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.ChannelOperationsHandler - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] Writing object FluxMapFuseable
22:15:21.719 [reactor-tcp-nio-4] DEBUG io.netty.util.Recycler - -dio.netty.recycler.maxCapacityPerThread: 32768
22:15:21.719 [reactor-tcp-nio-4] DEBUG io.netty.util.Recycler - -dio.netty.recycler.maxSharedCapacityFactor: 2
22:15:21.719 [reactor-tcp-nio-4] DEBUG io.netty.util.Recycler - -dio.netty.recycler.linkCapacity: 16
22:15:21.719 [reactor-tcp-nio-4] DEBUG io.netty.util.Recycler - -dio.netty.recycler.ratio: 8
22:15:21.742 [reactor-tcp-nio-4] DEBUG io.netty.buffer.AbstractByteBuf - -dio.netty.buffer.bytebuf.checkAccessible: true
22:15:21.756 [reactor-tcp-nio-4] DEBUG io.netty.util.ResourceLeakDetectorFactory - Loaded default ResourceLeakDetector: io.netty.util.ResourceLeakDetector@5c2a00d6
22:15:23.010 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] WRITE: 12B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 |Hello World! |
+--------+-------------------------------------------------+----------------+
22:15:25.042 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] FLUSH
22:15:27.861 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.FluxReceive - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] Subscribing inbound receiver [pending: 0,cancelled:false,inboundDone: false]
22:15:27.864 [reactor-tcp-nio-4] INFO reactor.Mono.Next.1 - onSubscribe(MonoNext.NextSubscriber)
22:15:27.869 [reactor-tcp-nio-4] INFO reactor.Mono.Next.1 - request(unbounded)
22:15:32.557 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] READ: 12B
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 |Hello World! |
+--------+-------------------------------------------------+----------------+
22:15:34.292 [reactor-tcp-nio-4] INFO reactor.Mono.Next.1 - onNext(Hello World!)
22:15:34.292 [reactor-tcp-nio-4] INFO reactor.Mono.Next.1 - onComplete()
22:15:34.293 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.ChannelOperations - [Channel] [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] User Handler requesting close connection
22:15:34.296 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] USER_EVENT: [Handler Terminated]
22:15:34.296 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.ChannelOperationsHandler - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] Disposing context reactor.ipc.netty.channel.PooledClientContextHandler@28add41a
22:15:34.296 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.channel.PooledClientContextHandler - Releasing channel: [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888]
22:15:34.297 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 - R:localhost/127.0.0.1:8888] CLOSE
22:15:35.967 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.resources.DefaultPoolResources - Released [id: 0x1ebe331c,L:/127.0.0.1:55386 ! R:localhost/127.0.0.1:8888],now 0 active connections
22:15:35.968 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 ! R:localhost/127.0.0.1:8888] READ COMPLETE
22:15:35.969 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 ! R:localhost/127.0.0.1:8888] INACTIVE
22:15:35.969 [reactor-tcp-nio-4] DEBUG reactor.ipc.netty.tcp.TcpClient - [id: 0x1ebe331c,L:/127.0.0.1:55386 ! R:localhost/127.0.0.1:8888] UNREGISTERED
注意这里channel的状态/操作变迁是ACTIVE->WRITE->FLUSH->READ->CLOSE->Released->READ COMPLETE->INACTIVE->UNREGISTERED
小结
- 可以看到TcpClient.newHandler在subscribe的时候触发Lambda表达式触发建立连接，最后调用的是Bootstrap.connect
- 而Bootstrap.connect则调用了MultithreadEventLoopGroup.register(channel)方法，其最后转为DefaultChannelPromise通过AbstractChannel$AbstractUnsafe来register
- AbstractChannel$AbstractUnsafe则是调用了taskQueue.offer(task)，来将这个register0(promise)放入eventLoop的taskQueue中
taskQueue是LinkedBlockingQueue，其大小是由DEFAULT_MAX_PENDING_TASKS这个参数来指定: Math.max(16,SystemPropertyUtil.getInt("io.netty.eventLoop.maxPendingTasks",Integer.MAX_VALUE))，默认是Integer.MAX_VALUE，也就是相当于无界了。
