netty Bootstrap connect方法

电玩女神 2022-04-04 03:07 327阅读 0赞

connect方法调用如下方法，值得分析

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 {
                            // Direclty 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, remoteAddress, localAddress, promise);
                            }
                        }
                    });
                    return promise;
                }
            }

initAndRegister：  
channel实例化：ReflectiveChannelFactory反射调用  
初始化：ChannelInitalizer加入pipeline，ChannelConfig 填充（来源于BootStrap），属性填充（来源于BootStrap）  
注册：生成DefaultChannelPromise，选择EventLoopGroup内的EventLoop（此时Channel的EventLoop就定下来了），提交register任务（channel注册到刚选出的EventLoop的selector上，不关注任何事件）到对应EventLoop，返回DefaultChannelPromise（ChannelFuture）

1 注册过程先选定特定的EventLoop，线程返回，由EventLoop完成实际注册并通知，若已完成且失败，返回用户，若已完成且成功，返回connect的future（新建）给用户，此时connect可能还没完成  
2 若注册未完成，返回PendingRegistrationPromise给用户，注册future的Listener通知PendingRegistrationPromise给到用户，避免用户也给注册future加listener，导致还未connect便先执行用户的listener