VPL NOTES FOR Hasan Adil For midterm - Farukh Khalid

What is .NET?

.NET is an integral part of many applications running on

Windows and provides common functionality for those

applications to run. This download is for people who

need .NET to run an application on their computer. For

developers, the .NET Framework provides a

comprehensive and consistent programming model for

building applications that have visually stunning user

experiences and seamless and secure communication.

The .NET Framework

The .NET Framework is a technology that supports building

and running the next generation of applications and XML

Web services. The .NET Framework is designed to fulfill the

following objectives:

To provide a consistent object-oriented programming

environment whether object code is stored and

executed locally, executed locally but Internet-

distributed, or executed remotely.

To provide a code-execution environment that

minimizes software deployment and versioning

conflicts.

To provide a code-execution environment that

promotes safe execution of code, including code

created by an unknown or semi-trusted third party.

To provide a code-execution environment that

eliminates the performance problems of scripted or

interpreted environments.

To make the developer experience consistent across

widely varying types of applications, such as

Windows-based applications and Web-based

applications.

To build all communication on industry standards to

ensure that code based on the .NET Framework can

integrate with any other code.

Microsoft .NET Framework is a software framework which

is installed in Microsoft Windows. Software which are

developed using .NET require .NET Framework to be

installed in your system to be able to run.

Once you install .NET Framework, it creates the required

software environment so that it can provide the

appropriate runtime requirements to the software.

The .NET Framework consists of the common language

runtime and the .NET Framework class library. The

common language runtime is the foundation of the .NET

Framework. You can think of the runtime as an agent that

manages code at execution time, providing core services

such as memory management, thread management, and

remoting, while also enforcing strict type safety and other

forms of code accuracy that promote security and

robustness. In fact, the concept of code management is a

fundamental principle of the runtime. Code that targets

the runtime is known as managed code, while code that

does not target the runtime is known as unmanaged code.

The class library is a comprehensive, object-oriented

collection of reusable types that you can use to develop

applications ranging from traditional command-line or

graphical user interface (GUI) applications to applications

based on the latest innovations provided by ASP.NET, such

as Web Forms and XML Web services.

Common Language Infrastructure (CLI)

Common Language Infrastructure (CLI) is a Microsoft

specification for running high-level language program

applications in different computer systems without

changing the application code. CLI is based on the

Microsoft .NET concept that some high-level language

programs require modifications due to system hardware

and processing constraints. CLI compiles applications as

Intermediate Language (IL), which is automatically

compiled as native system code. This approach allows

applications to run without code rewrites in limited

systems.

Common Type System (CTS)

The Common Type System (CTS) is a standard for defining

and using data types in the .NET framework. CTS defines

a collection of data types, which are used and managed by

the run time to facilitate cross-language integration.

Common Language Specification (CLS)

The Common Language Specification (CLS) is a

fundamental set of language features supported by the

Common Language Runtime (CLR) of the .NET Framework.

CLS is a part of the specifications of the .NET Framework.

CLS was designed to support language constructs

commonly used by developers and to produce verifiable

code, which allows all CLS-compliant languages to ensure

the type safety of code. CLS includes features common to

many object-oriented programming languages. It forms a

subset of the functionality of common type system (CTS)

and has more rules than defined in CTS.

Virtual Execution System (VES)

Virtual Execution System, or VES, is a component of the

Common Language Runtime (CLR) portion of the .NET

Framework. Its function is to provide a platform for

executing the managed code of an application.

Common Intermediate Language

CIL is a low level language based on the Common

language Infrastructure specification document. CIL was

earlier referred as MSIL (Microsoft Intermediate

Language) but later changed to CIL to standardize

the name of the language which is based on the

Common Language Infrastructure specification.

CIL is CPU and platform-independent instructions that

can be executed in any environment supporting the

Common Language Infrastructure, such as the .NET run

time or the cross-platform Mono run time. These

instructions are later processed by run time compiler and

is then converted into native language. CIL is an object-

oriented assembly language, and is entirelystack-based.

What is Common Language Runtime?

Common Language Runtime is the backbone of the .NET

framework. CLR takes care of a number of low-level

executions such as application hosting, thread handling,

memory management, security checks and application

performance. Its primary role is to locate, load, and

manage the .NET types (class, array, object etc.). The

term service refers to as a collection of services that are

required to execute a code. The beauty of CLR is that all

.NET-supported languages can be executed under this

single defined runtime layer. The spinal cord of CLR is

represented by a library refers to asmscoree.dll (common

object runtime execution engine). When an assembly is

referenced for use, mscoree.dll is automatically loaded.

The CLR first locates the referenced assembly, and then it

loads it into memory, compiles the associated IL code into

platform specific instructions, performs security related

checks, and finally executes the code.

In Depth, the .NET compilation process completes in two

stages; first, the C# code you write is compiled into an

Intermediate Code (MSIL). All .NET languages are

compiled into virtual identical IL code. The compiled file

with IL code is referred to as Assembly.

The second level of compilation happens just before the

application is executed. At this point, the IL code is

compiled into low-level native machine code. The Process

of Converting IL Code to native code will be done with

the help of JIT compiler (Just-In-Time Compiler). This

stage is known-as Just-In-Time (JIT) Compilation. Finally

.NET CLR produces the executable or library files and

executes the code.

The CLR (Common Language Runtime) is Microsoft's

implementation of the VES (Virtual Execution System).

The VES along with the CTS (Common Type System), the

CLS (common language specification) and the metadata

specification are all part of the CLI (Common Language

Infrastructure) specification.

The VES is a standardized virtual machine specification

that must be implemented in order to load and execute

CIL (Common Intermediate Language) modules (dll and

exe). A VES implementation also provide runtime services

such as garbage collection and security.

Common Language Runtime

As part of Microsoft's .NET Framework, the Common

Language Runtime (CLR) is programming that manages

the execution of programs written in any of several

supported languages, allowing them to share common

object-oriented classes written in any of the languages.

The Common Language Runtime is somewhat comparable

to the Java Virtual Machine that Sun Microsystems

furnishes for running programs compiled from the Java

language. Microsoft refers to its Common Language

Runtime as a "managed execution environment." A

program compiled for the CLR does not need a language-

specific execution environment and can easily be moved

to and run on any system with Windows 2000 or Windows

XP .

WHAT ARE LIB IN PROGRAMING

In computing, a library is a collection of similar objects that

are stored for occasional use - most frequently, programs

in source code or object code form, data files, scripts,

templates, fonts, and physical storage units such as tape

cartridges. Here are some common types of libraries.

1) A program library is a collection of (usually)

precompiled, reusable programming routines that a

programmer can "call" when writing code so that the

programmer doesn't have to write it. A dynamic link library

(DLL) is one type of program library. Another type of

program library is a class library, whose stored routines

are class definitions in object-oriented programming

(OOP). Graphical user interface (GUI) components such as

scroll bars, buttons, and windowing routines are generally

stored in a class library.

2) A storage library is a collection of physical storage

media such as tapes or disks and a way to access them. A

tape library, for example, contains tape cartridges and a

mechanism that moves them into and out of the drive(s)

where their content is read or updated.

3) A data library is the area of a data center (a centralized

area housing computer systems and equipment) where

storage media are archived. Online service providers also

sometimes refer to a directory on a server containing files

for downloading as a data library

Machine code: This is the most well-defined one. It is

code that uses the byte-code instructions which your

processor (the physical piece of metal that does the actual

work) understands and executes directly. All other code

must be translated or transformed into machine code

before your machine can execute it.

Native code: This term is sometimes used in places where

machine code (see above) is meant. However, it is also

sometimes used to mean unmanaged code (see below).

Unmanaged code and managed code: Unmanaged

code refers to code written in a programming language

such as C or C++, which is compiled directly into machine

code. It contrasts with managed code, which is written in

C#, VB.NET, Java, or similar, and executed in a virtual

environment (such as .NET or the JavaVM) which kind of

simulates a processor in software. The main difference is

that managed code manages the resources (mostly the

memory allocation) for you by employing garbage

collection and by keeping references to objects opaque.

Unmanaged code is the kind of code that requires you to

manually allocate and de-allocate memory, sometimes

causing memory leaks (when you forget to de-allocate)

and sometimes segmentation faults (when you de-allocate

too soon). Unmanaged also usually implies there are no

run-time checks for common errors such as null-pointer

dereferencing or array bounds overflow.

Strictly speaking, most dynamically-typed languages

such as Perl, Python, PHP and Ruby are alsomanaged

code. However, they are not commonly described as such,

which shows that managed code is actually somewhat of a

marketing term for the really big, serious, commercial

programming environments (.NET and Java).

Assembly code: This term generally refers to the kind of

source code people write when they really want to write

byte-code. An assembler is a program that turns this

source code into real byte-code. It is not acompiler

because the transformation is 1-to-1. However, the term

is ambiguous as to what kind of byte-code is used: it could

be managed or unmanaged. If it is unmanaged, the

resulting byte-code is machine code. If it is managed, it

results in the byte-code used behind-the-scenes by a

virtual environment such as .NET. Managed code (e.g. C#,

Java) is compiled into this special byte-code language,

which in the case of .NET is called Common Intermediate

Language (CIL) and in Java is called Java byte-code. There

is usually little need for the common programmer to access

this code or to write in this language directly, but when

people do, they often refer to it as assembly code because

they use an assembler to turn it into byte-code.

Namespaces in C#

Namespaces allow you to create a system to organize your

code. A good way to organize your namespaces is via a

hierarchical system.

Introduction

This article bring in you to C# Namespaces. In this article,

my objectives are as follows:

To give you the picture of what Namespace is?

Learn how to implement the "using" directive?

Learn to use "alias" directives.

Understand what are namespace members?

Need for Namespaces

Namespaces allow you to create a system to organize your

code. A good way to organize your namespaces is via a

hierarchical system. You put the more general names at

the top of the hierarchy and get more specific as you go

down. This hierarchical system can be represented by

nested namespaces. By placing code in different sub-

namespaces, you can keep your code organized.

The example:

namespace arun.CSharp.Namespaces

{

public class Hello

{

public string GetMessage()

{

return "Hello, world";

}

}

}

Namespaces are hierarchical, and the name

arun.CSharp.Namespaces is actually shorthand for

defining a namespace named arun that contains a

namespace named CSharp that itself contains a

namespace named Namespaces, as in:

namespace arun

{

namespace CSharp

{

namespace Namespaces

{....}

}

}

s

What is an Assembly

An assembly is a file that is automatically generated by

the compiler upon successful compilation of every .NET

application. It can be either a Dynamic Link Library or an

executable file. It is generated only once for an

application and upon each subsequent compilation the

assembly gets updated. However, a basic knowledge

about this topic will help you to understand the

architecture behind a .NET application.

An Assembly contains Intermediate Language (IL) code,

which is similar to Java byte code. In the .NET language,

it consists of metadata. Metadata enumerates the

features of every "type" inside the assembly or the

binary. In addition to metadata, assemblies also have a

special file called Manifest. It contains information about

the current version of the assembly and other related

information.

In .NET, there are two kinds of assemblies, such as

Single file and Multi file. A single file assembly contains

all the required information (IL, Metadata, and Manifest)

in a single package. The majority of assemblies in .NET

are made up of single file assemblies. Multi file

assemblies are composed of numerous .NET binaries or

modules and are generated for larger applications. One of

the assemblies will contain a manifest and others will

have IL and Metadata instructions.

Global assembly cache

GAC, global assembly cache is an area of memory

reserved to store the assemblies of all .NET applications

that are running on a certain machine.

It shares assemblies among multiple .NET applications.

The assemblies must have a strong name and must be

publicly shared to be installed in the GAC.

Passing Value-Type Parameters

A value-type variable contains its data directly as opposed

to a reference-type variable, which contains a reference to

its data. Passing a value-type variable to a method by

value means passing a copy of the variable to the method.

Any changes to the parameter that take place inside the

method have no effect on the original data stored in the

argument variable. If you want the called method to

change the value of the parameter, you must pass it by

reference, using the ref or out keyword. For simplicity, the

following examples use ref.

INDEXER

An indexer allows an object to be indexed like an array.

When you define an indexer for a class, this class behaves

like a virtual array. You can then access the instance of

this class using the array access operator ([ ]).

Simplify the interface

Boxing/ UnBoxing

C# allows us to convert a Value Type to a Reference Type,

and back again to Value Types . The operation of

Converting a Value Type to a Reference Type is called

Boxing and the reverse operation is called Unboxing.

Boxing

1: int Val = 1;

2: Object Obj = Val; //Boxing

The first line we created a Value Type Val and assigned a

value to Val. The second line , we created an instance of

Object Obj and assign the value of Val to Obj. From the

above operation (Object Obj = i ) we saw converting a

value of a Value Type into a value of a corresponding

Reference Type . These types of operation is called Boxing.

UnBoxing

1: int Val = 1;

2: Object Obj = Val; //Boxing

3: int i = (int)Obj; //Unboxing

The first two line shows how to Box a Value Type . The

next line (int i = (int) Obj) shows extracts the Value Type

from the Object . That is converting a value of a Reference

Type into a value of a Value Type. This operation is called

UnBoxing.

Boxing and UnBoxing are computationally expensive

processes. When a value type is boxed, an entirely new

object must be allocated and constructed , also the cast

required for UnBoxing is also expensive computationally.

What Is DLL

A DLL file is a resource within the Windows operating

system that contains code and data related to the

functionality of one or more applications. These files,

which may have the file extension .dll or other file

extensions, have been a major building block for the

Windows operating system and Windows programs since

the early MS-DOS versions of Microsofts computer

technology. Successive versions of Windows have

illustrated certain problems with the use of DLL files for

many different programs.

Anonymous method

Anonymous method is an inline un-named method in the

code.

>> It is created using the delegate keyword end doesnt

require name end return type and

Hence we can consider an anonymous method has only

body without name end return type.

Syntax:

delegate ( [argnfo] )

{ //statement(s) }

What is Lambda Expression?

A Lambda Expression is an anonymous function that we

can use to create a delegate or expression tree types.

Create a local functions that passes as an argument

Syntax:

(Input parameter) => (expression)

ADO.NET Connected & Disconnected Architecture

ADO.NET is a middleware technology used to connect

front end and back end of .NET applications.

ASP.NET is used to create front end of applications using

a code behind language like C#.NET.

Most of the applications require database as back end to

store application information.

To connect front end and back end ADO.NET is used.

It contains two types of architectures.

1. Connected architecture.

2. Disconnected architecture.

Two namespaces required to work with ADO.NET. They

are

System.Data.SqlClient

System.Data

SqlConnection class is used to create connection object

containing server, database and authentication details in

connection string.

SqlCommand class is used to create command object

which stores sql query which can be executed.

ADO.NET Connected architecture

In ADO.NET Connected architecture connection to the

database has to be in opened state to access the

database.

In Connected architecture connection string is used to

connect to the database.

Connection should be opened and closed.

Commands are executed using methods like

Method Commands Return type

ExecuteNonQuery Insert,Update,Delete,... int

ExecuteReader Select SqlDataReader

ExecuteScalar Aggregate commands Object

ExecuteNonQuery method is used to execute

commands and return number of rows effected.

ExecuteReader method is used to execute command

that retreives data and stores it in SqlDataReader which

is capable of reading data row by row. SqlDataReader is

read only and it reads in sequential order only.

Read( ) method of SqlDataReader is used to read data

row by row and it returns bool value.

ExecuteScalar method is used to execute sql command

that returns one value as its return type is object.

m.saadSticky NoteMarked set by m.saad

m.saadHighlight

m.saadSticky Notemost imprtant

If ExecuteScalar is used to execute select query that

retreives table data. It can return only first row first

column cell value.

ADO.NET Disconnected architecture

In ADO.NET disconnected architecture data is retrieved

from database and stored in dataset.

Data in dataset can be accessed even when the

connection to the database is closed.

SqlDataAdapter is used to open the connection ,execute

the command, store data in dataset and close the

connection.

DataSet is capable of storing more than one table.

DataSet is used to store data on client side.

da.fill(ds);

The above line of code is used to execute the command

by opening the connection to store data in dataset and

closing the connection.

Optimistic locking

As the name suggests optimistic it assumes that

multiple transaction will work without affecting each

other. In other words no locks are enforced while doing

optimistic locking. The transaction just verifies that no

other transaction has modified the data. In case of

modification the transaction is rolled back.

How does optimistic lock work?

You can implement optimistic locking by numerous ways

but the fundamental to implement optimistic locking

remains same. Its a 5 step process as shown below:-

Record the current timestamp.

Start changing the values.

Before updating check whether anyone else has

changed the values by checking the old time stamp and

new time stamp.

If its not equal rollbacks or else commit.

What are the different solutions by which we can

implement optimistic locking?

There are 3 primary ways by which we can implement

optimistic locking in .NET:-

Datasets: - Dataset by default implement optimistic

locking. They do a check of old values and new values

before updating.

Timestamp Data type: - Create a timestamp data type

in your table and while updating check if old timestamp is

equal to new timestamp.

Check old and new value: - Fetch the values, do the

changes and while doing the final updates check if the old

value and current values in database are equal. If they

are not equal then rollback or else commits the values.

Pessimistic locking

We can do pessimistic locking by specifying IsolationLevel in SQL Server stored procedures, ADO.NET level or by using transaction scope object.

What kind of locks can be acquired by using pessimistic locking?

There are 4 kinds of locks you can acquire Shared, Exclusive, Update and intent. The first two are actual locks while the other two are hybrid locks and marker.

When to use? Reads

Allowed

Writes

Allowed

Shared lock

When you want only to read

and you do not want any other

transactions to do update.

Yes No

Exclusive

When you want to modify data

and you do not want anyone to

read the transaction, neither

you want anyone to update.

No No

Update lock

This is a hybrid lock. This lock

is used when you want to do

update operation which passes

through multiple phases before

the actual update happens. It

first starts with shared lock in

the read phase and then on the

actual update it acquires an

exclusive lock.

Read phase Yes No

Manipulating phase Yes No

Update phas No No

Intent Lock (

Demand

locks)

Intent lock is for lock hierarchy.

This lock is used when you

want to lock resources down in

the hierarchy. For example a

shared intent lock on a table

means shared locks are placed

on pages and rows with the

table.

NA NA

Schema locks When you are changing table

structure. No No

Bulk update

locks

Used when you are doing bulk

updates

Table

level No

Table

level No

VPL NOTES FOR Hasan Adil For midterm - Farukh KhalidWhat is .NET?Common Language Infrastructure (CLI)Common Intermediate LanguageWhat kind of locks can be acquired by using pessimistic locking?