netty 4 pipeline 顺序图解

发表于

刚开始写 netty 的时候， 会对 pipeline 很疑惑， 其实并不复杂。

netty 4 pipeline 图解

首先看一下 event 是如何流动的：

netty4 pipeline

不过更好的说明是在 Java Document 中, 推荐阅读一下, 很有帮助: io.netty.channel.ChannelPipeline

How an event flows in a pipeline

The following diagram describes how I/O events are processed by ChannelHandlers in a ChannelPipeline typically. An I/O event is handled by either a ChannelInboundHandler or a ChannelOutboundHandler and be forwarded to its closest handler by calling the event propagation methods defined in ChannelHandlerContext, such as ChannelHandlerContext.fireChannelRead(Object) and ChannelHandlerContext.write(Object).
...

这个图更形象：





                                               I/O Request
                                          via Channel or
                                      ChannelHandlerContext
                                                    |
+---------------------------------------------------+---------------+
|                           ChannelPipeline         |               |
|                                                  \|/              |
|    +---------------------+            +-----------+----------+    |
|    | Inbound Handler  N  |            | Outbound Handler  1  |    |
|    +----------+----------+            +-----------+----------+    |
|              /|\                                  |               |
|               |                                  \|/              |
|    +----------+----------+            +-----------+----------+    |
|    | Inbound Handler N-1 |            | Outbound Handler  2  |    |
|    +----------+----------+            +-----------+----------+    |
|              /|\                                  .               |
|               .                                   .               |
| ChannelHandlerContext.fireIN_EVT() ChannelHandlerContext.OUT_EVT()|
|        [ method call]                       [method call]         |
|               .                                   .               |
|               .                                  \|/              |
|    +----------+----------+            +-----------+----------+    |
|    | Inbound Handler  2  |            | Outbound Handler M-1 |    |
|    +----------+----------+            +-----------+----------+    |
|              /|\                                  |               |
|               |                                  \|/              |
|    +----------+----------+            +-----------+----------+    |
|    | Inbound Handler  1  |            | Outbound Handler  M  |    |
|    +----------+----------+            +-----------+----------+    |
|              /|\                                  |               |
+---------------+-----------------------------------+---------------+
                |                                  \|/
+---------------+-----------------------------------+---------------+
|               |                                   |               |
|       [ Socket.read() ]                    [ Socket.write() ]     |
|                                                                   |
|  Netty Internal I/O Threads (Transport Implementation)            |
+-------------------------------------------------------------------+

写代码

那么, 在代码中如何体现这种顺序呢 ?

如下所示 :

ChannelPipeline p = ...;
p.addLast("1", new InboundHandlerA());
p.addLast("2", new InboundHandlerB());
p.addLast("3", new OutboundHandlerA());
p.addLast("4", new OutboundHandlerB());
p.addLast("5", new InboundOutboundHandlerX());

当 inbound event 到来时, handler 顺序是 12345, 而 outbound 时, 顺序是 54321.

不过:

  1. 因为3和4没有实现 ChannelInboundHandler , 所以 inbound 事件的顺序是 125
  • 因为1和2没有实现ChannelOutboundHandler, 所以outbound时间是543
  • 因为5实现了 ChannelInboundHandler 和 ChannelOutboundHandler, 所以 inbound 和 outbound event 都会经过.

参考