从源代码看 ObjC 中消息的发送

旧城等待， 2023-10-16 23:56 11阅读 0赞

本文授权转自：[draveness][]

因为ObjC的runtime只能在MacOS下才能编译，所以文章中的代码都是在MacOS，也就是x86\_64架构下运行的，对于在arm64中运行的代码会特别说明。

**写在前面**

如果你点开这篇文章，相信你对Objective-C比较熟悉，并且有多年使用Objective-C编程的经验，这篇文章会假设你知道：

1.  在Objective-C中的“方法调用”其实应该叫做消息传递
2.  \[receivermessage\]会被翻译为objc\_msgSend(receiver,@selector(message))
3.  在消息的响应链中可能会调用-resolveInstanceMethod:或者-forwardInvocation:等方法
4.  关于选择子SEL的知识
    
    如果对于上述的知识不够了解，可以看一下这篇文章Objective-CRuntime，但是其中关于objc\_class的结构体的代码已经过时了，不过不影响阅读以及理解。
5.  方法在内存中存储的位置，深入解析ObjC中方法的结构
    
    文章中不会刻意区别方法和函数、消息传递和方法调用之间的区别。
6.  能翻墙（会有一个Youtube的链接）

**概述**

关于Objective-C中的消息传递的文章真的是太多了，而这篇文章又与其它文章有什么不同呢？

由于这个系列的文章都是对Objective-C源代码的分析，所以会从Objective-C源代码中分析并合理地推测一些关于消息传递的问题。

**关于@selector()你需要知道的**

因为在Objective-C中，所有的消息传递中的“消息“都会被转换成一个selector作为objc\_msgSend函数的参数：

这里面使用@selector(hello)生成的选择子**SEL**是这一节中关注的重点。

我们需要预先解决的问题是：使用@selector(hello)生成的选择子，是否会因为类的不同而不同？各位读者可以自己思考一下。

先放出结论：使用@selector()生成的选择子不会因为类的不同而改变，其内存地址在编译期间就已经确定了。也就是说**向不同的类发送相同的消息时，其生成的选择子是完全相同的。**

接下来，我们开始验证这一结论的正确性，这是程序主要包含的代码：

在主函数任意位置打一个断点，比如->\[objecthello\];这里，然后在lldb中输入：

![2016-04-25-objc-message-selector.png][]

这里面我们打印了两个选择子的地址@selector(hello)以及@selector(undefined\_hello\_method)，需要注意的是：

@selector(hello)是在编译期间就声明的选择子，而后者在编译期间并不存在，undefined\_hello\_method选择子由于是在运行时生成的，所以内存地址明显比hello大很多

如果我们修改程序的代码：

![2016-04-25-objc-message-selector-undefined.png][]

在这里，由于我们在代码中显示地写出了@selector(undefined\_hello\_method)，所以在lldb中再次打印这个sel内存地址跟之前相比有了很大的改变。

更重要的是，我没有通过指针的操作来获取hello选择子的内存地址，而只是通过@selector(hello)就可以返回一个选择子。

从上面的这些现象，可以推断出选择子有以下的特性：

1.  Objective-C为我们维护了一个巨大的选择子表
2.  在使用@selector()时会从这个选择子表中根据选择子的名字查找对应的SEL。如果没有找到，则会生成一个SEL并添加到表中
3.  在编译期间会扫描全部的头文件和实现文件将其中的方法以及使用@selector()生成的选择子加入到选择子表中

在运行时初始化之前，打印hello选择子的的内存地址：

![2016-04-25-objc-message-find-selector-before-init.png][]

**message.h文件**

Objective-C中objc\_msgSend的实现并没有开源，它只存在于message.h这个头文件中。

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     </div> 
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     </div> 
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      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">OBJC_EXPORTidobjc_msgSend(idself,SELop,...)</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

在这个头文件的注释中对消息发送的一系列方法解释得非常清楚：

当编译器遇到一个方法调用时，它会将方法的调用翻译成以下函数中的一个objc\_msgSend、objc\_msgSend\_stret、objc\_msgSendSuper和objc\_msgSendSuper\_stret。发送给对象的父类的消息会使用objc\_msgSendSuper有数据结构作为返回值的方法会使用objc\_msgSendSuper\_stret或objc\_msgSend\_stret其它的消息都是使用objc\_msgSend发送的

在这篇文章中，我们只会对消息发送的过程进行分析，而不会对上述消息发送方法的区别进行分析，默认都使用objc\_msgSend函数。

**objc\_msgSend调用栈**

这一小节会以向XXObject的实例发送hello消息为例，在Xcode中观察整个消息发送的过程中调用栈的变化，再来看一下程序的代码：

在调用hello方法的这一行打一个断点，当我们尝试进入（Stepin）这个方法只会直接跳入这个方法的实现，而不会进入objc\_msgSend：

![2016-04-25-objc-message-wrong-step-in.gif][]

因为objc\_msgSend是一个私有方法，我们没有办法进入它的实现，但是，我们却可以在objc\_msgSend的调用栈中“截下”这个函数调用的过程。

调用objc\_msgSend时，传入了self以及SEL参数。

既然要执行对应的方法，肯定要寻找选择子对应的实现。

在objc-runtime-new.mm文件中有一个函数lookUpImpOrForward，这个函数的作用就是查找方法的实现，于是运行程序，在运行到hello这一行时，激活lookUpImpOrForward函数中的断点。

![2016-04-25-objc-message-youtube-preview.jpg][]

由于转成gif实在是太大了，笔者试着用各种方法生成动图，然而效果也不是很理想，只能贴一个Youtube的视频链接，不过对于能够翻墙的开发者们，应该也不是什么问题吧（手动微笑）

如果跟着视频看这个方法的调用栈有些混乱的话，也是正常的。在下一个节中会对其调用栈进行详细的分析。

**解析objc\_msgSend**

对objc\_msgSend解析总共分两个步骤，我们会向XXObject的实例发送两次hello消息，分别模拟无缓存和有缓存两种情况下的调用栈。

**无缓存**

在->\[objecthello\]这里增加一个断点，当程序运行到这一行时，再向lookUpImpOrForward函数的第一行添加断点，确保是捕获@selector(hello)的调用栈，而不是调用其它选择子的调用栈。

![2016-04-25-objc-message-first-call-hello.png][]

由图中的变量区域可以了解，传入的选择子为"hello"，对应的类是XXObject。所以我们可以确信这就是当调用hello方法时执行的函数。在Xcode左侧能看到方法的调用栈：

调用栈在这里告诉我们：lookUpImpOrForward并不是objc\_msgSend直接调用的，而是通过\_class\_lookupMethodAndLoadCache3方法：

这是一个仅提供给派发器（dispatcher）用于方法查找的函数，其它的代码都应该使用lookUpImpOrNil()（不会进行方法转发）。\_class\_lookupMethodAndLoadCache3会传入cache=NO避免在没有加锁的时候对缓存进行查找，因为派发器已经做过这件事情了。

**实现的查找lookUpImpOrForward**

由于实现的查找方法lookUpImpOrForward涉及很多函数的调用，所以我们将它分成以下几个部分来分析：

1.  无锁的缓存查找
2.  如果类没有实现（isRealized）或者初始化（isInitialized），实现或者初始化类
3.  加锁
4.  缓存以及当前类中方法的查找
5.  尝试查找父类的缓存以及方法列表
6.  没有找到实现，尝试方法解析器
7.  进行消息转发
8.  解锁、返回实现

**无锁的缓存查找**

下面是在没有加锁的时候对缓存进行查找，提高缓存使用的性能：

不过因为\_class\_lookupMethodAndLoadCache3传入的cache=NO，所以这里会直接跳过if中代码的执行，在objc\_msgSend中已经使用汇编代码查找过了。

**类的实现和初始化**

在Objective-C运行时初始化的过程中会对其中的类进行第一次初始化也就是执行realizeClass方法，为类分配可读写结构体class\_rw\_t的空间，并返回正确的类结构体。

而\_class\_initialize方法会调用类的initialize方法，我会在之后的文章中对类的初始化进行分析。

**加锁**

加锁这一部分只有一行简单的代码，其主要目的保证方法查找以及缓存填充（cache-fill）的原子性，保证在运行以下代码时不会有新方法添加导致缓存被冲洗（flush）。

**在当前类中查找实现**

实现很简单，先调用了cache\_getImp从某个类的cache属性中获取选择子对应的实现：

*  ![2016-04-25-objc-message-cache-struct.png][]

不过cache\_getImp的实现目测是不开源的，同时也是汇编写的，在我们尝试stepin的时候进入了如下的汇编代码。

![objc-message-step-in-cache-getimp][]

它会进入一个CacheLookup的标签，获取实现，使用汇编的原因还是因为要加速整个实现查找的过程，其原理推测是在类的cache中寻找对应的实现，只是做了一些性能上的优化。

如果查找到实现，就会跳转到done标签，因为我们在这个小结中的假设是无缓存的（第一次调用hello方法），所以会进入下面的代码块，从类的方法列表中寻找方法的实现：

调用getMethodNoSuper\_nolock方法查找对应的方法的结构体指针method\_t：

因为类中数据的方法列表methods是一个二维数组method\_array\_t，写一个for循环遍历整个方法列表，而这个search\_method\_list的实现也特别简单：

findMethodInSortedMethodList方法对有序方法列表进行线性探测，返回方法结构体method\_t。

如果在这里找到了方法的实现，将它加入类的缓存中，这个操作最后是由cache\_fill\_nolock方法来完成的：

如果缓存中的内容大于容量的3/4就会扩充缓存，使缓存的大小翻倍。

在缓存翻倍的过程中，当前类全部的缓存都会被清空，Objective-C出于性能的考虑不会将原有缓存的bucket\_t拷贝到新初始化的内存中。

找到第一个空的bucket\_t，以(SEL,IMP)的形式填充进去。

**在父类中寻找实现**

这一部分与上面的实现基本上是一样的，只是多了一个循环用来判断根类：

1.  查找缓存
2.  搜索方法列表

与当前类寻找实现的区别是：在父类中寻找到的\_objc\_msgForward\_impcache实现会交给当前类来处理。

**方法决议**

选择子在当前类和父类中都没有找到实现，就进入了方法决议（methodresolve）的过程：

这部分代码调用\_class\_resolveMethod来解析没有找到实现的方法。

根据当前的类是不是元类在\_class\_resolveInstanceMethod和\_class\_resolveClassMethod中选择一个进行调用。

这两个方法的实现其实就是判断当前类是否实现了resolveInstanceMethod:或者resolveClassMethod:方法，然后用objc\_msgSend执行上述方法，并传入需要决议的选择子。

关于resolveInstanceMethod之后可能会写一篇文章专门介绍，不过关于这个方法的文章也确实不少，在Google上搜索会有很多的文章。

在执行了resolveInstanceMethod:之后，会跳转到retry标签，重新执行查找方法实现的流程，只不过不会再调用resolveInstanceMethod:方法了（将triedResolver标记为YES）。

**消息转发**

在缓存、当前类、父类以及resolveInstanceMethod:都没有解决实现查找的问题时，Objective-C还为我们提供了最后一次翻身的机会，进行方法转发：

返回实现\_objc\_msgForward\_impcache，然后加入缓存。

====

这样就结束了整个方法第一次的调用过程，缓存没有命中，但是在当前类的方法列表中找到了hello方法的实现，调用了该方法。

![objc-message-first-call-hello][]

**缓存命中**

如果使用对应的选择子时，缓存命中了，那么情况就大不相同了，我们修改主程序中的代码：

然后在第二次调用hello方法时，加一个断点：

![objc-message-objc-msgSend-with-cache][]

objc\_msgSend并没有走lookupImpOrForward这个方法，而是直接结束，打印了另一个hello字符串。

我们如何确定objc\_msgSend的实现到底是什么呢？其实我们没有办法来确认它的实现，因为这个函数的实现使用汇编写的，并且实现是不开源的。

不过，我们需要确定它是否真的访问了类中的缓存来加速实现寻找的过程。

好，现在重新运行程序至第二个hello方法调用之前：

![objc-message-before-flush-cache][]

打印缓存中bucket的内容：

<table style="border-collapse:collapse; border-spacing:0px; width:720px; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; background:none!important"> 
 <tbody style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; background:none!important"> 
  <tr style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; background:none!important"> 
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    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
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      17 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      18 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      19 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      20 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      21 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      22 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      23 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      24 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      25 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      26 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      27 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      28 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      29 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      30 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      31 
    </div> 
    <div style="margin:0px!important; padding:0px 0.5em 0px 1em!important; border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(108,226,108)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important">
      32 
    </div> </td> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:680px; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; background:none!important"> 
    <div style="margin:0px!important; padding:0px!important; min-height:auto!important; height:auto!important; border:0px!important; bottom:auto!important; float:none!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:relative!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; background:none!important"> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p(objc_class*)[XXObjectclass]</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(objc_class*)$0=0x0000000100001230</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p(cache_t*)0x0000000100001240</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(cache_t*)$1=0x0000000100001240</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p*$1</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(cache_t)$2={ </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_buckets=0x0000000100604bd0</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_mask=3</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_occupied=2</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">}</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p$2.capacity()</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(mask_t)$3=4</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p$2.buckets()[0]</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(bucket_t)$4={ </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_key=0</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_imp=0x0000000000000000</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">}</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p$2.buckets()[1]</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(bucket_t)$5={ </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_key=0</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_imp=0x0000000000000000</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">}</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p$2.buckets()[2]</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(bucket_t)$6={ </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_key=4294971294</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_imp=0x0000000100000e60(debug-objc`-[XXObjecthello]atXXObject.m:17)</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">}</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(lldb)p$2.buckets()[3]</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">(bucket_t)$7={ </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_key=4300169955</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">_imp=0x00000001000622e0(libobjc.A.dylib`-[NSObjectinit]atNSObject.mm:2216)</code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-weight:normal!important; font-style:normal!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:none white!important"> 
      <code style="margin:0px!important; padding:0px!important; font-style:normal!important; font-weight:normal!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; text-align:left!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:auto!important; color:black!important; background:none!important">}</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

在这个缓存中只有对hello和init方法实现的缓存，我们要将其中hello的缓存清空：

![objc-message-after-flush-cache][]

这样XXObject中就不存在hello方法对应实现的缓存了。然后继续运行程序：

![objc-message-after-flush-cache][objc-message-after-flush-cache 1]

虽然第二次调用hello方法，但是因为我们清除了hello的缓存，所以，会再次进入lookupImpOrForward方法。

下面会换一种方法验证猜测：在hello调用之前添加缓存。

添加一个新的实现cached\_imp：

我们将以@selector(hello),cached\_imp为键值对，将其添加到类结构体的缓存中，这里的实现cached\_imp有一些区别，它会打印@"CachedHello"而不是@"Hello"字符串：

在第一个hello方法调用之前将实现加入缓存：

![objc-message-after-flush-cache][objc-message-after-flush-cache 2]

可以看到，我们虽然没有改变hello方法的实现，但是在objc\_msgSend的消息发送链路中，使用错误的缓存实现cached\_imp拦截了实现的查找，打印出了CachedHello。

由此可以推定，objc\_msgSend在实现中确实检查了缓存。如果没有缓存会调用lookupImpOrForward进行方法查找。

为了提高消息传递的效率，ObjC对objc\_msgSend以及cache\_getImp使用了汇编语言来编写。

**小结**

这篇文章与其说是讲ObjC中的消息发送的过程，不如说是讲方法的实现是如何查找的。

Objective-C中实现查找的路径还是比较符合直觉的：

缓存命中

查找当前类的缓存及方法

查找父类的缓存及方法

方法决议

消息转发

文章中关于方法调用栈的视频最开始是用gif做的，不过由于gif时间较长，试了很多的gif转换器，都没有得到一个较好的质量和合适的大小，所以最后选择用一个Youtube的视频。

参考资料

[深入解析ObjC中方法的结构][ObjC]

[Objective-CRuntime][]

[Let'sBuildobjc\_msgSend][Let_sBuildobjc_msgSend]

[draveness]: http://draveness.me/message/
[2016-04-25-objc-message-selector.png]: http://cc.cocimg.com/api/uploads/20160512/1463032066691606.png
[2016-04-25-objc-message-selector-undefined.png]: http://cc.cocimg.com/api/uploads/20160512/1463032112608293.png
[2016-04-25-objc-message-find-selector-before-init.png]: http://cc.cocimg.com/api/uploads/20160512/1463032153484376.png
[2016-04-25-objc-message-wrong-step-in.gif]: http://cc.cocimg.com/api/uploads/20160512/1463032237534640.gif
[2016-04-25-objc-message-youtube-preview.jpg]: http://cc.cocimg.com/api/uploads/20160512/1463032284858530.jpg
[2016-04-25-objc-message-first-call-hello.png]: http://cc.cocimg.com/api/uploads/20160512/1463032329433780.png
[2016-04-25-objc-message-cache-struct.png]: http://cc.cocimg.com/api/uploads/20160512/1463032459804922.png
[objc-message-step-in-cache-getimp]: http://cc.cocimg.com/api/uploads/image/20160512/1463032475174548.png
[objc-message-first-call-hello]: http://cc.cocimg.com/api/uploads/image/20160512/1463032619646033.png
[objc-message-objc-msgSend-with-cache]: http://cc.cocimg.com/api/uploads/image/20160512/1463032638905648.gif
[objc-message-before-flush-cache]: http://cc.cocimg.com/api/uploads/image/20160512/1463032655315420.png
[objc-message-after-flush-cache]: http://cc.cocimg.com/api/uploads/image/20160512/1463032693345641.png
[objc-message-after-flush-cache 1]: http://cc.cocimg.com/api/uploads/image/20160512/1463032703224589.png
[objc-message-after-flush-cache 2]: http://cc.cocimg.com/api/uploads/image/20160512/1463032788141712.png
[ObjC]: https://github.com/Draveness/iOS-Source-Code-Analyze/blob/master/objc/%E6%B7%B1%E5%85%A5%E8%A7%A3%E6%9E%90%20ObjC%20%E4%B8%AD%E6%96%B9%E6%B3%95%E7%9A%84%E7%BB%93%E6%9E%84.md
[Objective-CRuntime]: http://tech.glowing.com/cn/objective-c-runtime/
[Let_sBuildobjc_msgSend]: https://www.mikeash.com/pyblog/friday-qa-2012-11-16-lets-build-objc_msgsend.html