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This article mainly explains "what is the implementation model of CLR". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the implementation model of CLR".

It is very easy to write the Hello World of C# with IDE such as Visual Studio, but can you print out Hello World without IDE? This is not to say to work away from IDE, but to learn the execution model of CLR.

Hello World

Create a new notepad, enter the following code, and save as HelloWorld.txt.

Using System; namespaceHelloWorld {classProgram {static voidMain (string [] args) {Console.WriteLine ("HelloWorld!"); Console.ReadKey ();}

Open the Visual Studio 2008 command prompt

But change to the directory of HelloWorld.txt.

Run the command: csc / out:Hello.exe HelloWorld.txt

If there is no accident, Hello.exe will be compiled and Hello World will be printed.

CLR execution Model-compilation time

The execution process of the CLR program is roughly divided into two steps, the compile time and the run time, which is roughly shown in the following figure:

Logically, the compilation period can also be divided into two steps:

The CLR (C #) compiler accepts source code files and compiles them into managed modules. The managed module includes IL code, metadata, CLR header and other components. In the above example, HelloWorld.txt is compiled into a managed module.

General assemblies contain a lot of source code files (only HelloWorld.txt here) and resource files. The second step is to merge each source code file and resource file into an assembly corresponding to the compilation results.

Perform the above two steps to get a XX.dll or XX.exe assembly. Just like the Hello.exe above.

How does the compiler know to compile to a managed module or a resource file? In fact, it is necessary to tell the compiler how to compile each file, which corresponds to the generation operation of the file attributes of Visual Studio.

Right-click the file of any Visual Studio solution resource solution-- > Properties-- > build operation:

Specify Class1 as the embedded resource, look at it with ILSpy and you will find that you only embed Class1 in the assembly, named: namespace. File name:

You can even set a picture to compile and let the compiler try to compile it, but it will report an error.

Operation period

The above generated assembly, the assembly is IL code, it is not runnable code. Il is a machine language independent of CPU. It is not compiled into native code (CPU instruction) by the JIT (Just-in-Time) compiler until the assembly is called. At run time, CLR performs the following steps:

◆ checks the security features of an assembly

◆ allocates space in memory

◆ sends the executable code in the assembly to the JIT compiler and compiles part of the cost machine code (CPU instruction).

The executable code of the assembly is compiled by JIT when needed, and then the native code (CPU instruction) is cached for execution in later programs. Once the application is terminated, the compiled native code will also be discarded.

For example, if you change the above code to:

Static void Main (string [] args) {Console.WriteLine ("Hello"); Console.WriteLine ("World!"); Console.ReadKey ();}

* WriteLine needs to be compiled by JIT before execution. Because the WriteLine code has been compiled, the second WriteLine directly executes the code in the memory block, skipping JIT compilation.

Due to the allocation of memory, JIT compilation process, etc., so the program will cause some performance loss when running *, this feeling is obvious when writing ASP.NET, press F5 will wait a long time to display the home page.

Let's simulate and feel the process. To extend the memory allocation time with a large number of classes, refer to this file HelloWorld.css (blog Park does not support txt format):

Run the command again: csc / out:Hello.exe HelloWorld.txt, get the Hello.exe, and print out the HelloWorld only if there is a certain delay in execution.

Generate native code

Using the NGen.exe provided by. Net, IL code can be compiled into cost machine code. Can solve the above problem. NGen.exe has two functions:

Speed up the startup of the application. Because the code has been compiled to native code, the runtime does not need to take time to compile

Reduce the assembly of the application. If an assembly loads multiple processes at the same time, IL compiles the costing machine code and saves it to a separate file. In this way, the code can be shared by memory mapping to multiple processes at the same time. Avoid one code per process.

Run the Visual Studio 2008 command prompt again

Run the following command: ngen install Hello.exe:

Running Hello.exe after the command completes (it takes about 10 seconds on my machine until I can type the command again) will find that Hello World can be printed out immediately without any delay.

For ASP.NET,Microsoft also provides aspnet_compiler.exe, we can build a script (.bat) precompiler in the ASP.NET program. The following is an example (the program of from Lao Zhao):

% SYSTEMROOT%\ Microsoft.NET\ Framework\ v2.0.50727\ aspnet_compiler-v /-p.\ MyMvcDemo.Web.UI-f-errorstack.\ Compliled PAUSE Thank you for your reading. The above is the content of "what is the implementation model of CLR". After the study of this article, I believe you have a deeper understanding of what the implementation model of CLR is, and the specific use needs to be verified by practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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