Ngen.exe -- A discussion -- Some Queries (.NET Framework Tools Series)

1) Go to the Visual Studio command prompt and type

2) You will see the below details

Administrative options:
/show Show existing native images (show all if no args)
/delete Delete existing native images (delete all if no args)
Developer options:
/debug Generate image which can be used under a debugger
/debugopt Generate image which can be used under a debugger in optimized debugging mode
/prof Generate image which can be used under a profiler
Miscellaneous options:
/? or /help Show this message
/nologo Prevents displaying of logo
/silent Prevents displaying of success messages
Usage : ngen [options] <assembly path or display name>

Runtime tries to look out for that assembly. If it is unable to find the assembly than it reverts back to JIT.

Incase the application is running in a debug mode than .NET runtime looks for a native image created with /debug or /debugopt option.

The CPU type.
The version of the operating system.
The exact identity of the assembly (recompilation changes identity).
The exact identity of all assemblies that the assembly references.

Since the native assembly image is machine specific its validity depends on all the above factors. Well the are number of scenarios when the native image can become invalid :

• .NET Framework updation causes all native images to become invalid.
• Computer CPU updation
• Any Changes made to the OS.
• Recompilation of an assembly to IL causes existing native images of that assembly to become invalid.
• Recompliation of a referenced assembly causes the native image to the refrencing assembly to become invalid.
• Change in machine security policy.

Hence if there is any change in the computer setting or environment then there are chances of the Native Image becoming invalid.

Note : Its just that the assembly native image has become invalid not the assembly. hence next time the assembly will be loaded with (JIT) its native image will not be loaded.

Native Image generator creates a local image of an .NET Assembly and installs that image in the native cache on the local machine. But when you create a Native Image of an ASP.NET assembly the .NET Runtime ignores that assembly and reverts back to JIT. This is because CLR cannot load native images in a shared application domain and all ASP.NET applications run in a shared application domain. Hence although the native image of the assembly will be created it will not be installed in the image cache.

To run Ngen as a part of your application deployment or setup create a custom action during installation which will run the ngen and create images for all your application assemblies. Similarly also create a custom action in you deployment project during uninstallation to remove them from the native cache.

These were questions that I had in my mind ... if u have any other let me know .... if u have more thought opinions about these questions pls post them.

Going ahead lets just explore a few options of Ngen.exe

To view all the assemblies in the native cache use the/show option