Managed Code and Application Domains

Shivanand Arur

Actually i downloaded a PDF file from this website and i was reading the topic called "managed code" and i found it very interesting. But i got stuck at a paragraph which is as follows:

"Application domains, a concept introduced in .NET, permit multiple applications to run in a singleprocess. Before managed code runs, it goes through a verification procedure to establish that it will
not access memory or perform an action that would cause the process to crash. If the code passes
this verification, it is said to be type safe. Type-safe code allows the CLR to define application
domains, which carry the same level of isolation and protection as a process. While not totally free
of charge, interapplication communication, across application domains, avoids most of the
performance penalties associated with interprocess communication."

The problem is, i found it very difficult to understand from the second line of the paragraph.. Please help me undertand this by giving a simple example since i am a beginner!!Also if possible, please give me some links to understand more about Managed Code!! Hope to get some good replies.. Thanks in advance....

2 Replies

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Vulpes15y ago
Accepted answer
In Windows, programs run in what are called 'processes'. Normally, each program runs in its own process which ensures that it won't interfere with other programs which are running at the same time by writing to the memory they are using and so forth.

Now before a program which is written in managed code is allowed to run, it has to go through a verification process to ensure that it is 'type safe' and won't write to memory which it doesn't own or otherwise interfere with other running programs.

This means that the rule that every program needs to run in its own process can be relaxed for managed code and it is possible for several programs (or assemblies as they called) to run in the same process with each assembly having its own 'Application Domain' within that process.

Application domains serve much the same function as processes for unmanaged programs but they are more lightweight and don't use as many operating system resources as processes do. It is also easier for programs to communicate across application domain boundaries than across process boundaries.

In practice, not many managed programs make use of application domains 'explicitly' though they are created in the background in certain types of applications, notably ASP.NET applications, even though the programmer may not be aware of this.
Shivanand Arur15y ago
Thank you very much Vulpes.... The way you have explained is really really good.... My concept about "Type safety and Managed Code" is very much clear now... Thank you once again!!!