通过openjdk源码分析ObjectMonitor底层实现

秒速五厘米 2024-03-23 10:35 44阅读 0赞

在我们分析synchronized关键字底层信息时，其中谈到了Monitor对象，它是由C++来实现的，那，到底它长啥样呢？我们在编写同步代码时完全木有看到该对象的存在，所以这次打算真正来瞅一下它的真正面目，而对于这个Hospot代码JDK是并没有开源的，但是社区版本的JDK是开源了，在openjdk上可以阅读得到，所以下面先到openjdk上瞅一下：

![fea9134b85984854842e972f779eb1fd.png][]

所以点击后

![5179576c42c048d8918b0ac6ea03f9c5.png][]

点击

![4fc19db089a74f32b7297bb71568941c.png][]

继续点击

![efa5a10f314c431db6d527c80ba88ce7.png][] 然后点击左侧browse

![c9d25268a1ad4a62bacbadcd1afcd612.png][]

定位到这个路径

![c7d117f2c0a7431287450573164388d2.png][]

点击runtime

![82f37d7cbf8c49b6a65febc54eb43e40.png][]

其中我们想看到的Monitor对象的源代码就在其中，如下：

![df4f46478f864f33a8f9f0a8beb307d7.png][]

其中.hpp是c++的头文件，其具体的实现是以cpp中，接下来就得打开它们来看我们想了解的东东了，是不是很刺激？对于上一次理论中提到了两个东东：

![d4cb8f2ed6ce4471875df0c02b823f66.png][]

那咱们从源码中来看一下具体都表现为啥，首先先来看一下ObjectMonitor.hpp：

![dbd64d2527c24a03a6556355735306dd.png][]

接下来就可以看到ObjectMonitor的类声明了：

![8c87c93bef9d4ab996da6d805a6c66e1.png][]

其实对就对应于：

![4b2fbe3c9c5c4953be6bcb783f60ec25.png][]

接下来挑里面的重点内容瞅一下：

![6605868ff7e243c6a28add1049898255.png][]

接下来看一下它的成员变量：

![c9d0add262a549e3a25b7eaf2a23bb5c.png][]

那看一下\_WaitSet的定义：

![9f5aa980dd43420c95986c6090a3a74f.png][]

再看一下\_EntryList的定义：

![ad2c1b3ddd7742b6948354c37601b76a.png][]

另外在理论中提到

![8f865180b0a74a3ca2a6ca579863a618.png][] 其实也在底层有定义，如下：![c6778fc571bb4e01bb0beeaf4c601e2c.png][]

看一下他的定义

![9299fc50b8494a398af77d1473e25ad6.png][]

另外上理论中还提到了它：

![fe6418e3b8c84e53acc5dc05a141a020.png][]

其实也有对应

![7f99ec8a27b543cebba308f037138be8.png][] 继续来看其他的一个成员变量

![937948340a8245f1a4a91ae4f15151ab.png][]

![d81949e6d4784c76afbf6d260df7ea51.png][] 以及

![f868cbeee10343d594e8d6997496206c.png][]

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