JIT具体过程

最新推荐文章于 2024-10-16 19:32:00 发布

原创最新推荐文章于 2024-10-16 19:32:00 发布 · 860 阅读

CC 4.0 BY-SA版权

文章标签：

119 篇文章

订阅专栏

本文详细解析了CLR（Common Language Runtime）在首次和重复调用方法时的执行流程，包括从代码编译到内存分配和本地代码执行的全过程。重点介绍了JIT（Just-In-Time）编译器如何将字节码编译为机器码，并讨论了在不同运行环境中JIT编译的策略，如浏览器与服务器端。

Calling a method for the first time:

Your program code calls a method Foo()
The CLR looks at the type that implements Foo() and gets the metadata associated with it
From the metadata, the CLR knows what memory address the IL (Intermediate byte code) is stored in.
The CLR allocates a block of memory, and calls the JIT.
The JIT compiles the IL into native code, places it into the allocated memory, and then changes the function pointer in Foo()'s type metadata to point to this native code.
The native code is ran.

Calling a method for the second time:

Your program code calls a method Foo()
The CLR looks at the type that implements Foo() and finds the function pointer in the metadata.
The native code at this memory location is ran.

第二次调用跟C/C++本地码差不多了

正常解释:一条字节码(语义信息不足)翻译成若干机器码

JIT:一坨字节码(根据整体语义进行优化)编译成机器码,缓存起来,方便下次使用

如果在浏览器这种只运行一次脚本的的环境,则只需部分JIT;而在服务器端要多次运行的环境,则把所有的代码JIT,方便多次使用

Hotspot:一部分JIT,一部分正常解释