Netty(十一)——Unsafe容貌之揭

Dear 丶 2022-04-16 05:48 122阅读 0赞

上一篇 末尾简单提到了JDK的Unsafe类，其实是调用了一些底层的Native的一些方法实现，不希望用户调用的。而Netty中的Unsafe类实际上也是Channel的辅助类，不应该被用户直接调用的。实际的IO的读写操作都是有Unsafe完成的。好，我们简单总结一下。

一，AIP接口功能列表：

<table>  Unsafe-API功能  
 <tbody> 
  <tr> 
   <td style="width:30px;">序号</td> 
   <td style="width:363px;">接口</td> 
   <td style="width:470px;">注释</td> 
  </tr> 
  <tr> 
   <td style="width:30px;">1，</td> 
   <td style="width:363px;"> <pre><code>RecvByteBufAllocator.Handle recvBufAllocHandle();</code></pre> </td> 
   <td style="width:470px;">Return the assigned {@link RecvByteBufAllocator.Handle} which will be used to allocate {@link ByteBuf}'s when receiving data.</td> 
  </tr> 
  <tr> 
   <td style="width:30px;">2，</td> 
   <td style="width:363px;"> <pre><code>ChannelHandlerInvoker invoker();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Returns the {@link ChannelHandlerInvoker} which is used by default unless specified by a user.
</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">3，</td> 
   <td style="width:363px;"> <pre><code>SocketAddress localAddress();</code></pre> </td> 
   <td style="width:470px;"> <pre><code> Return the {@link SocketAddress} to which is bound local or {@code null} if none.
</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">4，</td> 
   <td style="width:363px;"> <pre><code>SocketAddress remoteAddress();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Return the {@link SocketAddress} to which is bound remote or {@code null} if none is bound yet.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">5，</td> 
   <td style="width:363px;"> <pre><code>void register(EventLoop eventLoop, ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;">Register the {@link Channel} of the {@link ChannelPromise} and notify the {@link ChannelFuture} once the registration was complete.<br> It's only safe to submit a new task to the {@link EventLoop} from within a {@link ChannelHandler} once the {@link ChannelPromise} succeeded. Otherwise the task may or may not be rejected.</td> 
  </tr> 
  <tr> 
   <td style="width:30px;">6，</td> 
   <td style="width:363px;"> <pre><code>void bind(SocketAddress localAddress, ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Bind the {@link SocketAddress} to the {@link Channel} of the {@link ChannelPromise} and notify it once its done.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">7，</td> 
   <td style="width:363px;"> <pre><code>void connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Connect the {@link Channel} of the given {@link ChannelFuture} with the given remote {@link SocketAddress}.
If a specific local {@link SocketAddress} should be used it need to be given as argument. Otherwise just pass {@code null} to it.
The {@link ChannelPromise} will get notified once the connect operation was complete.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">8，</td> 
   <td style="width:363px;"> <pre><code>void disconnect(ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Disconnect the {@link Channel} of the {@link ChannelFuture} and notify the {@link ChannelPromise} once the operation was complete.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">9，</td> 
   <td style="width:363px;"> <pre><code>void close(ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Close the {@link Channel} of the {@link ChannelPromise} and notify the {@link ChannelPromise} once the operation was complete.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">10，</td> 
   <td style="width:363px;"> <pre><code>void closeForcibly();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Closes the {@link Channel} immediately without firing any events.  Probably only useful when registration attempt failed.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">11，</td> 
   <td style="width:363px;"> <pre><code>void deregister(ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Deregister the {@link Channel} of the {@link ChannelPromise} from {@link EventLoop} and notify the {@link ChannelPromise} once the operation was complete.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">12，</td> 
   <td style="width:363px;"> <pre><code>void beginRead();</code></pre> </td> 
   <td style="width:470px;">Schedules a read operation that fills the inbound buffer of the first {@link ChannelHandler} in the {@link ChannelPipeline}. &nbsp;If there's already a pending read operation, this method does nothing.</td> 
  </tr> 
  <tr> 
   <td style="width:30px;">13，</td> 
   <td style="width:363px;"> <pre><code>void write(Object msg, ChannelPromise promise);</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Schedules a write operation.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">14，</td> 
   <td style="width:363px;"> <pre><code>void flush();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Flush out all write operations scheduled via {@link #write(Object, ChannelPromise)}.</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">15，</td> 
   <td style="width:363px;"> <pre><code>ChannelPromise voidPromise();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Return a special ChannelPromise which can be reused and passed to the operations in {@link Unsafe}. It will never be notified of a success or error and so is only a placeholder for operations that take a {@link ChannelPromise} as argument but for which you not want to get notified.
</code></pre> </td> 
  </tr> 
  <tr> 
   <td style="width:30px;">16，</td> 
   <td style="width:363px;"> <pre><code>ChannelOutboundBuffer outboundBuffer();</code></pre> </td> 
   <td style="width:470px;"> <pre><code>Returns the {@link ChannelOutboundBuffer} of the {@link Channel} where the pending write requests are stored.</code></pre> </td> 
  </tr> 
 </tbody> 
</table>

二，Unsafe的关系结构图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdWppYWhhbjYyOTYyOQ_size_16_color_FFFFFF_t_70][]

三，阅读源码：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdWppYWhhbjYyOTYyOQ_size_16_color_FFFFFF_t_70 1][]

由于Channel的很多实现都是通过子类Unsafe来完成的，所以，这篇我们学习总结了一下Unsafe，这种方式是不是值得我们学习一下，不让希望外部直接调用的情况下，来帮助父类完成更多底层的东西。

PS：[Unsafe总结思维导图][Unsafe]。

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[Unsafe]: https://download.csdn.net/download/liujiahan629629/10791432