Q9. What is precompilation in ASP.NET 2.0? What is a pre-compiled website?
A9. When the first request arrives at your web application there is a mind-numbing amount of work to do. The worker process starts, the runtime initializes, ASPX pages are parsed and compiled to intermediate language, methods are just-in-time compiled to native code - and the list goes on and on. If you want to cut out some of the overhead and improve the startup time of your application, then you’ll want to look at the precompile features in ASP.NET 2.0.
Although pre-compilation will give our site a performance boost, the difference in speed will only be noticeable during the first request to each folder. Perhaps a more important benefit is the new deployment option made available by the precompile - the option to deploy a site without copying any of the original source code to the server. This includes the code and markup in aspx, ascx, and master files.
There are 2 types of pre-compilation:
(i) In Place Precompilation
(ii) Precompilation for Deployment
In Place Precompilation -> By default, ASP.NET dynamically parses and compiles all the ASPX pages in a folder when the first request arrives for a page inside that folder. ASP.NET also needs to compile applicable files in the special folders, like App_Code, on the first request, and any code-behind files associated with ASPX and ASCX files. The runtime caches all the compilation results in order to quickly process later requests, and does not need to recompile again unless someone edits a file. This behavior gives us a great deal of flexibility, including the flexibility to change code and arkup and instantly have the changes reflected in the next browser request.
The price for this flexibility is the performance hit on the first request. Some people have found their ASP.NET applications to be slow starters. These people usually work in the sales department and perform software demos in front of customers. In place pre-compilation makes the “first hit” to a web application and forces all pages and code in the application to compile.
The tool to use for pre-compilation is the aspnet_compiler executable, which you can find in the %WINDIR%\Microsoft.NET\Framework\v2.x.xxxx directory. If we have a web application in the WebSite1 virtual directory under IIS, we could use the following command line to compile the pplication.
C:\Windows\Microsoft.NET\Framework\v2.0.50215>aspnet_compiler -v /Website1
The –v parameter specifies that we are passing a virtual path to our web site. On servers with multiple websites you may need
to use the –m parameter and specify the full IIS metabase path to the application (-m /LM/W3SVC/1/Root/WebSite1).
The pre-compiled code will end up inside of the Temporary ASP.NET File directory, just as it would when the runtime compiles files for a browser request. Inside of the bin directory for the compiled site, you’ll find the assemblies (dll files). The compiler generates special filenames to avoid naming collisions. In the shot below, the dll starting with App_Code contains the code from the App_Code directory – not too surprising. Each folder containing aspx, or ascx files will compile into a dll prefixed with App_Web. The files with a .compiled extension contain XML with information about which original source code file maps to which assembly.
You may find these files in the following location of your computer.
C:\windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files
With the compiled files in place your web application should have a slightly better startup time, but a primary benefit to in place pre-compilation will be the ability to ensure the web application is error free. If you happen to modify a class or web form and leave an error in the file, the aspnet_compiler will fail and display the compiler error. The tool will also display any warnings, but warning will not stop compilation.
Pre-compilation For Deployment --> Pre-compilation for deployment creates an ‘executable’ (no source code) version of your web application. With pre-compilation for deployment you give the aspnet_compiler the path to your source code, and the path to a target directory for the compilation results, like below.
aspnet_compiler -p "C:\MyDevelopment\WebSite1" -v / C:\MyStage
This command will compile the site and place the result in C:\Staging. You must still specify –v as a parameter, even though we are not using a virtual path as either a source or a destination. Instead, the compiler will use this parameter to resolve application root references (~).
The pre-compilation for deployment step will recreate your web site’s folder structure in the destination directory. All of the static files (HTML files, image files, configuration files) are copied into the folder structure exactly as they appear in the source folder hierarchy. A bin directory will appear in the target directory with all of the assemblies and .compiled files.
The target directory will contain no source code. All of the classes in the App_Code folder are now compiled into one or more assemblies in the bin directory, and no .cs or .vb files will exist in the target directory. Master page files will also compile to the bin directory and not exist. All the code and markup in ASPX, ASCX, and ASHX files, along with any associated code-behind files, will live inside of one or more assemblies in the bin directory, although these files will still exist in the target directory, they exist as nearly empty ‘marker’ files. If you open an ASPX file in a pre-compiled target directory you’ll see the following content:
This is a marker file generated by the precompilation tool, and should not be deleted!
Once the application finishes compiling you can FTP or XCOPY the target directory to a web server (or map a virtual directory to the target directory), and the application will be ready to run. A benefit to pre-compilation for deployment is that no one can make changes to the web application by tweaking the source code – no source code exists! In fact, you can’t even place a new ASPX file into the existing application directory structure without causing an error.
Q10. If a web application is pre-compiled, How do you make changes to it?
A10. Making a change to your site will require you to make a change in the original source code, pre-compile the application again, and redeploy all files to the server.
When we recompile an already pre-compiled website, what should be kept in mind?
Pre-compilation generates unique filenames for some assemblies in the bin folder, and these filenames will change each time the pre-compiler executes. The first time you run aspnet_compiler you might see App_Web_murhs6vm.dll in the bin directory, the next time you might see App_Web_gvohdjw.dll with the same compiled code, even though no source file has changed. This means you might have unneeded dlls in your bin directory if you keep repeatedly copy files to the server without cleanup.
Update: use the -fixednames switch to generate repeatable assembly names.