- 这篇将是网络层源码分析的最后一篇
- 北京的天,无力吐槽啊~
- 快年底了, 每个团队都在旁边录制新年寄语,各种口号~
对nio的封装:Selector类
- 所在文件: clients/src/main/java/org/apache/kafka/commmon/network/Selector.java
- 源码中的注释:
A nioSelector interface for doing non-blocking multi-connection network I/O. This class works with NetworkSend} and NetworkReceive to transmit size-delimited network requests and responses.
- 重要函数解析:
(1) register(String id, SocketChannel socketChannel): 注册这个socketChannel到一个nio selector, 将其读事件添加到selector的监听队列; 这个socketChannel通常是服务器接收到的客户端的连接:
SelectionKey key = socketChannel.register(nioSelector, SelectionKey.OP_READ);
同时创建KafkaChannel, 负责实际的数据接收和发送:
KafkaChannel channel = channelBuilder.buildChannel(id, key, maxReceiveSize);
key.attach(channel);
this.channels.put(id, channel);
上面的id即为我们在上篇介绍的非常重要的ConnectionId;
(2) connect: 使用nio的SocketChannel连接到给定的地址,并且注册到nio selector,同时也创建了KafkaChannel,负责实际的数据接收和发送;
SocketChannel socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
Socket socket = socketChannel.socket();
socket.setKeepAlive(true);
socketChannel.connect(address);
SelectionKey key = socketChannel.register(nioSelector, SelectionKey.OP_CONNECT);
KafkaChannel channel = channelBuilder.buildChannel(id, key, maxReceiveSize);
key.attach(channel);
this.channels.put(id, channel);
(3) poll: 核心函数:
Do whatever I/O can be done on each connection without blocking. This includes completing connections, completing disconnections, initiating new sends, or making progress on in-progress sends or receives.
处理作为客户端的主动连接事件:
if (key.isConnectable()) {
channel.finishConnect();
this.connected.add(channel.id());
this.sensors.connectionCreated.record();
}
处理连接建立或接收后的ssl握手或sasl签权操作:
if (channel.isConnected() && !channel.ready())
channel.prepare();
处理触发的读事件:
if (channel.ready() && key.isReadable() && !hasStagedReceive(channel)) {
NetworkReceive networkReceive;
while ((networkReceive = channel.read()) != null)
addToStagedReceives(channel, networkReceive);
}
使用一个while循环力求每次读事件触发时都读尽可能多的数据;
channel.read()里会作拆包处理(后面会讲到),返回非null表示当前返回的NetworkReceive里包含了完整的应用层协议数据;
处理触发的写事件:
if (channel.ready() && key.isWritable()) {
Send send = channel.write();
if (send != null) {
this.completedSends.add(send);
this.sensors.recordBytesSent(channel.id(), send.size());
}
}
需要发送数据通过调用Selector::send方法,设置封装了写数据的NetworkSend,再将这个NetworkSend通过KafkaChannel::setSend接口设置到KafkaChannel,同时将写事件添加到selector的监听队列中,等待写事件被触发后,通过KafkaChannel::write将数据发送出去;
addToCompletedReceives()
将当前接收到的完整的的request到添加到completedReceives中,上一篇中介绍的SocketServer会作completedReceives中取出这些request作处理;
封装对单个连接的读写操作:KafkaChannel类
- 所在文件: clients/src/main/java/org/apache/kafka/common/network/KafkaChannel.java
- 包括transportLayer和authenticator, 完成ssh握手,sasl签权,数据的接收和发送;
传输层:TransportLayer类
- 所在文件 clients/src/main/java/org/apache/kafka/common/network/TransportLayer.java
- 两个子类: PlanintextTransportLayer和SslTransportLayer
- PlanintextTransportLayer的实现主要是通过NetworkReceive和NetworkSend;
- SslTransportLayer的实现主要是通过SocketChannel,ByteBuffers和SSLEngine实际了加密数据的接收和发送(看到ssl就头大啊,这部分先忽略~~~);
Kafka协议的包结构:
- 前4个字节固定, 值是后面的实际数据的长度;
- NetworkReceive: 接收时先接收4个字节, 获取到长度,然后再接收实际的数据;
- NetworkSend: 发送时实际数据前先加上4个字节的数据长度再发送;
上图:
