Scott Hanselman posted some of the .Net interview questions on his blog, dividing it into several segments. I tried to answer them in parts, in little elaborated way, by putting definitions with answers. You really can’t get away with Google to do it all. I took reference from some websites to elaborate the definition. Here goes part I of the series…

Everyone who writes code…

• Describe the difference between a Thread and a Process?

Process:  A process is a single executable module (.Exe file) that runs concurrently with other executable modules. For example, an internet browser and a word processor can run simultaneously. Processes are separate executable, loadable modules (as opposed to threads). One process can’t affect other processes running in same multitasking environment.

Thread: Threads in contrary are the tasks that run concurrently with other tasks within a single executable file.  Within the same process, they can affect each other.  One process can contain any number of threads.

Example: From within a data base application, a user may start both a spell check and a sorting operation.  Contrast this with multiple .EXE files (processes) like a word processor, a data base, and internet browser, multi-tasking under OS/2 for example.

• What is a Windows Service and how does its lifecycle differ from a "standard" EXE? 

Windows services are long running process (applications) that are ideal for use in server environments. These applications do not have user interface and they do not produce any visual output. Its lifecycle is managed by “Service Control Manager” which is responsible for starting and stopping the service. They do not require a logged in user in order to execute and can run under the context of any user including the system. On the other hand, a “Standard executable” doesn’t require Control Manager and is directly related to the visual output.

• What is the maximum amount of memory any single process on Windows can address? Is this different than the maximum virtual memory for the system? How would this affect a system design?

Windows provides a page-based virtual memory management scheme that allows applications to realize a 32-bit linear address space for 4 gigabytes (GB) of memory. As a result, each application has its own private address space from which it can use the lower 2 GB—the system reserves the upper 2 GB of every process's address space for its own use.

 Figure: A process in Windows NT has a 4-GB linear address space, of which the lower 2 GB is available for applications to use.

As illustrated in Figure, each process can address up to 4 GB of memory using 32-bit linear addresses. The upper half of the address space is reserved for use by the system. Because the system is the same for each process, regardless of the subsystem it runs on, similar pages of system memory are typically mapped to each process in the same relative location for efficiency.

DLL is An abbreviation for dynamic link library, a file containing a collection of Windows functions designed to perform a specific class of operations An EXE contains an entry point to start execution { main() in C/C++ and  Public Static Void Main() in .Net  } whereas functions within DLLs are called (invoked) by applications (EXEs) as necessary to perform the desired operation.

• What is strong-typing versus weak-typing? Which is preferred? Why?

 Strict enforcement of type rules with no exceptions is strong-typing. In a strongly typed language, type usage can be detected at compile time rather then run-time. In these languages, conversion between types requires use of explicit conversion functions as opposed to implicit type coercion in weak-typed (batter called run-typed) languages.

As a common assumption, strong typing catches more errors at compile time than weak typing, resulting in fewer run-time exceptions (but still is a disputable point when it comes to "which one to use").

• Corillian's product is a "Component Container." Name at least 3 component containers that ship now with the Windows Server Family.

Microsoft first announced C# and the .NET Framework in summer 2000, calling C# 'The first component-oriented language in the C/C++ family.'  The essence of component development is not to build what you can buy, on the basis that snapping together pre-tested parts is faster, cheaper and probably more reliable than coding everything for yourself.

As a definition, almost any class file is a component. Moreover, it can easily be compiled to a DLL, it benefits from .NET versioning, and it can be reused. The existence of components also implies the existence of containers, which again may be visual or non-visual. The container plays an important role in component management. In particular, all containers implement IDisposable, which means they have a Dispose method for releasing unmanaged resources such as window handles or open files. In their Dispose method, containers must also call Dispose on all the components they host. In the .NET Framework both ASP.NET Web Forms and rich client Windows Forms are visual component containers.  System.Web.UI.Page, System.Windows.Forms.Form and System.ComponentModel.Container are few other component containers which ship with Windows Server Family.

• What is a PID? How is it useful when troubleshooting a system?

PID stands for Process Identifier, a uniquely assigned integer that identifies a process in the operating system. In any system, applications use PID to identify the process uniquely. Also, it is used in diagnosing the problems with the process in Multi-Tasking systems.

• How many processes can listen on a single TCP/IP port?

Probably ONE, if you need to create another TCP/IP listener, you need to set-up a different port.

• What is the GAC? What problem does it solve?

Each computer on which the common language runtime is installed has a machine-wide code cache called the global assembly cache (GAC). Assemblies deployed in the global assembly cache must have a strong name. A developer tool named "Global Assembly Cache tool" (Gacutil.exe), provided by the .NET Framework SDK can be used to deploy assemblies to GAC. The global assembly cache stores assemblies specifically designated to be shared by several applications on the computer. It provides us the way to overcome “DLL Hell” problem also.

         Cheers..

Enjoy!!

(Via Sean Hull)

When it comes to Web development these days, you have a lot of options. Many of these methods involve preprocessing—that is, embedding code into HTML pages with special tags that signal to a preprocessor that they contain code, and that it should do something with it. Much like a CGI, this code is then run on the server, and it returns some content, which then assumes part of the shape of the resulting HTML page sent back to the browser. Both the open source scripting language PHP and languages within Microsoft's ASP.NET framework fall into this category; JavaServer Pages (JSP) and Perl/Mason operate this way as well. More

Sean Hull is the senior consultant at his firm, iHeavy Inc., in New York City. He focuses on integrating open source technologies with commercial technologies such as Oracle, and has serviced many successful New York companies.

Via John Mueller.

Configuration—the act of modifying the settings for an assembly—is becoming an essential part of .NET development. The .NET Framework 1.1 Configuration Utility provides a means of configuring the assemblies on your system in different ways.

This article explains why assemblies require configuration, shows how to use the .NET Framework 1.1 Configuration Utility to perform the task, and explores an alternative you can try in some cases. More...

I received an article from a friend few days back, which provides evidence of Microsoft platform usage in Enterprise mission critical applications.  IT provides some interesting facts. Though I can't post the full article here, gist of the same is below..

Main points

• Gartner Custom Research conducted the study, which is random sample and projectable across lorgs in US
• While this does not represent the opinion of Gartner Analysts, MS worked extensively with the analysts to create the survey and validate the methodology.
• MS have also done extensive reviews of the data with Gartner analysts, who have largely maintained J2EE + Unix dominates in the mission-critical apps space ("enterprise apps").  This data shows otherwise. 
• Since the focus of this survey is mission-critical LOB applications, this study (at request of Gartner analysts), excludes email, meaning it does not include Windows Servers running Exchange.  

The Highlights  ( all questions are for Mission Critical Apps within lorgs US Only):

• Server OS Usage (multi select) - Windows leads with 65%. Commercial Unixes combined add up to 58%
• Server OS Share (single select - primary mission critical OS) - Windows leads with 36.5%. Commercial Unixes combined add up to 35.3% .
• Application Platform Usage (multi select) - Microsoft (.net & other) leads with 41%. J2EE is right behind with 40%.
• Application Platform Share (single select - primary mission critical platform) - Microsoft leads with 25%. J2EE follows with 22%.
• Mission Critical Vendors - Microsoft leads with 25%, with IBM close behind at 24%.
• Web Services Usage & Vendor - 44% of Enterprises are doing WS, Microsoft is the clear vendor leader with 45% share, followed by IBM at 20%.
• SOA Usage & Vendor - 31% of Enterprises are doing SOA, Microsoft is the clear vendor leader with 39% share, followed by IBM at 19%.
  

       Interesting huh!!!

Today, somebody asked me about the difference between constant and readonly type declarations and about when to use which one. Here is the interesting detailed comparison with three different examples…

a) private const int EXAMPLE1 = 450;
b) private static readonly DateTime EXAPMLE2 = DateTime.Now
c) private readonly DateTime EXAMPLE3 = DateTime.Now;

The Difference:

1) Compile-time Constants

Symbols defined as const (EXAMPLE1 in this case) are replaced with the value of the constant at COMPILE TIME. Therefore statement if (ValueInConst == EXAMPLE1) would get converted to the same MSIL as if (ValueInConst == 450). The compiler replaces the symbol with the value of the constant. This is the main point to compile-time constants.  Compile-time constants can only be used effectively for built-in integral and floating-point types (primitive types), enums, or strings. These are the only types that allow you to assign meaningful constant values as part of the initialization process.  The IL generated for a compile-time constant contains the value, not the symbol. The value is "burned in" at compile time.

2) Readonly Values

Readonly values are those constants which cannot be modified after the constructor has executed. Readonly values are different, however, in that they're set at run time. You have much more flexibility in working with run time constants. Run-Time constants can be of any type; as long as you can assign them in your constructors, they will work. I could not create DateTime values with const but I can make readonly values from DateTime structures.

Secondly, readonly values can be used for instance constants, storing different values for each instance of the class type. The main distinction is that readonly values are resolved at run time. The Intermediate Language generated when you reference a readonly constant reference the readonly variable, not the value.

Which one to use?

The main difference between const and readonly fields is in their flexibility. Suppose you've defined both const and readonly fields like below:

public class SomeValues 
{ 
   public static readonly constOne = 2; 
   public const constTwo = 5; 
} 

Then, in an application these values are referenced and displayed using likely sum statement.

Console.WriteLine("Sum is {0}",SomeValues.constOne + SomeValues.constTwo); 

If you run above snippet, Output will be “Sum is 7”.

After few days you release a new version of the assembly with the following changes:

public class SomeValues
{ 
   public static readonly constOne = 50;
   public const constTwo = 30; 
}

You distribute the assembly without rebuilding the application assembly. You'll get an absurd result as “Sum is 55” !!!!. The snippet now uses the value 50 as constOne, and 5 (OLD VALUE) as constTwo. The const value of cosntTwo (5) was placed into the application assembly by the compiler. On the other hand, constOne was declared as readonly, so it gets resolved at run time. Therefore, the application assembly uses the new value without recompiling the application assembly. Simply installing an updated version of the Infrastructure assembly is enough. Another advantage is that using readonly constants generates smaller sized assembly. Whenever you use a const value, compiler has to inserts the value of the constant. On the contrary, when you reference a readonly value compiler references that symbol not the value. On the flip side, readonly type doesn't work to initialize an attribute. The actual value of the object must be available at compile time for the attribute to get created correctly. Therefore, only values declared as const (or enums) can be used in this instance.

One major advantage constants provide over readonly is that it can be used in places where readonly values cannot be used (as in Attributes). You can use const values as the parameters to attribute constructors but you can’t use readonly values, or variables

There are some small performance gains using const instead of readonly but if you want to have little flexibility, readonly declaration has it for you. This flexibility overrides the small performance gains from using const. Everything except attribute parameters and enums should be declared readonly.

Via Leo

I encountered a very informative post about ASP.Net page life cycle on an equally informative blog from Leo.

Any ASP.NET developer should know the inner workings of the ASP.NET engine. The Page control is its backbone. Knowing the control lifecycle in the page considerably helps in the day-to-day and advanced development projects. read more..

Of course there are lotsa websites having articles on the similar topic but this one takes the bet because of it's beautiful graphical representation (a picture speaks thousands words )

Microsoft has reported a security issue which affects web content owners who are running any version of ASP.NET on Microsoft Windows 2000, Windows 2000 Server, Windows XP Professional, and Windows Server 2003...

A security flaw in Microsoft's ASP.NET technology could allow intruders to enter password-protected areas of a web site by altering a URL. A fix is not yet available, but Microsoft is offfering guidelines to help ASP.NET users secure their sites against intrusion attempts. The flaw exists only in ASP.NET, not ASP (Active Server Pages). Read More.

I got back on line today, though temporarily I'll be blogging from a friend's place.

Probably it will be few more days when I'll be able to get DSL at my home and start netting from there.

Cheers till then!!