Multithreading in C#

• It is an approach which allows a single program to perform multiple actions simultaneously.  Earlier we had an approach of multitasking where in this case we can execute multiple programs at a given point of time. Operating system is responsible for multitasking where all operating systems are not multitasking Operating system. Windows. MAC, Linux are multitasking Operating systems whereas DOS is a single tasking Operating system. If we want to develop a multithreaded application first the support should be available under the programming language whereas the language will internally take the support of Operating system again. C# language supports multitasking.
• A thread is a unit of execution which is responsible in executing the program known as main thread. So by default every language is multithreaded.
• In a single threaded program the execution takes place by performing its actions one by one ie suppose it has started calling a method until and unless that method execution is completed it cannot go to the other methods for execution. So if at all a method is taking more time to execute than the expected until that time all the other methods has to wait.
• to overcome the problems with single threaded applications, multithreading was designed wherein multithreading we can use a separate thread for calling each method.

• Multithreading has been designed for maximum utilization of CPU resources. So multithreaded applications execute adopting 2 principals.

1. Time Sharing: Here Operating system allocates time period for each thread for executing the methods and transfers the control to another thread once the time is elapsed giving equal importance for all the threads to execute.
2. Maximum utilization of resources: This comes into picture only if the first principal violates ie if a thread could not execute in its given time period for some reason without wasting at that thread Operating system transfers the control to the other threads in execution.

How to define an exception class ?

If we want to define an exception class we  need to adopt the following process:

1. Define a class by inheriting from predefined class exception so that a new class is also an exception.
2. Overwrite the message properly and provide the error message that has to be given when the exception occurred.

Add a new class DivideByOddNoException and  write the following code:

 

using System;

namespace CSharpConsole
{
    class DivideByOddNoException: Exception 
    {
        public override string Message
        {
            get
            {
                return "Attempted to divide by odd number ";
            }
        }
   }
}
 Add a new class ThrowDemo.cs and write the following code:

using System;

namespace CSharpConsole
{
    class ThrowDemo
    {
        static void Main()
        {
            int x, y, z;
            Console.Write("Enter x value ");
            x = int.Parse(Console.ReadLine());
            Console.Write("Enter y value ");
            y = int.Parse(Console.ReadLine());
            if (y % 2 > 0)
            {
                throw new DivideByOddNoException();
                //throw new ApplicationException("Divisor should not be an odd number ");
            }
            z = x / y;
            Console.WriteLine(z);
            Console.WriteLine("End of program ");
        }
    }
}

Exceptions in C#

When we write a program there are chances of coming across 2 different types of errors

• Compile-time Errors
• Run-time Errors.

An error which comes into picture at the time of program compilation is a compile-time error which may occur due to syntax mistakes. An error which occurs in the middle of the programs execution is known as a run-time error and these errors occur due to various reasons like wrong implementation of logic, wrong inputs supplied to a program, missing of required resources etc. 

A compile-time error is not dangerous because it occurs at the time of compilation whereas run-time errors are dangerous because they occur in the program when the execution is going on and if at all a run-time error occurs in a program, the program terminates abnormally on the same line where the error gets occured without executing the rest of the code.

Note:  Whenever an error situation occurs in a program the exception handler comes into picture to identify the type of error and then creates an object of an exception class associated with that error and throws that object and that object will first terminate the program abnormally and then displays an error message associated with an exception object.

Exception Handling

Whenever a run- time error occurs under the program abnormal termination is occuring so we will be facing so many problems in the application. To overcome the problems we are provided with a mechanism known as Exception Handling.

Exception Handling is a process of stopping the abnormal termination of the program whenever the exceptions are terminating the program in case of run time error. If we can stop the abnormal termination of a program we will be getting following advantages :

• We can make the statement which are not associated with the error.
• We can display a user friendly error message to the end user so that he can resolve the error, got occurred provided if it is in his hands.
• We can also perform some corrective actions to come out of a problems that may occur due to error.

To handle an exception we need to enclose our code under some special blocks known as try catch block which should be used as following:

try

{

-statements which requires execution when the run time error occurs.

-statements which does not require execution only when the run time error occurs.

}

catch

{

-statements which requires execution only when the run time error occurs.

}

[--< multiple catch blocks if required >--]

Add a class Exception demo.cs and write the following code:

using System;

namespace CSharpConsole
{
    class ExceptionDemo
    {
        static void Main()
        {
            int x, y, z;
            try
            {
                Console.WriteLine("Enter x value: ");
                x = int.Parse(Console.ReadLine());

                Console.WriteLine("Enter y value: ");
                y = int.Parse(Console.ReadLine());

                z = x / y;
                Console.WriteLine(z);
            }
            catch (DivideByZeroException ex1) //ex1 is a variable of class          DivideByZeroException
            {
                Console.WriteLine("Divisor must not be zero");
            }
            catch (FormatException ex2) //ex2 is a variable of class FormatException
            {
                Console.WriteLine("Input must be numeric");
            }

            catch (Exception ex3)
            {
                Console.WriteLine(ex3.Message);//message is a read only property
            }
            {
                Console.WriteLine("End of the program");
                Console.ReadLine();
            }
         }
    }
}

Types of Delegates

Delegates are of two types:

• Unicast Delegate
• Multicast Delegate

If a delegate is used for calling a single method we call it as a unicast delegate whereas if a delegate is use for calling multiple methods its a multicast delegate.
In case of the methods delegate, a single delegate call will execute all the methods that are bound with the delegate.

using System;

namespace CSharpConsole
{
    public  delegate void MathDel(int x, int y);
    class DelMulti
    {
        public void Add(int x, int y)
        {
            Console.WriteLine("Add:  " + (x + y));
        }
        public void Sub(int x, int y)
        {
            Console.WriteLine("Sub:  " + (x - y));
        }
        public void Mul(int x, int y)
        {
            Console.WriteLine("mul:  " + (x * y));
        }
        public void Div(int x, int y)
        {
            Console.WriteLine("Div:  " + (x / y));
        }
        static void Main()
        {
            DelMulti obj = new DelMulti();
            MathDel md=new MathDel (obj.Add );
            md+=obj.Sub ;md +=obj.Mul ;md +=obj.Div ;
            md(100,25);
            Console .WriteLine ();
            md(600,30);
            Console .WriteLine ();
            md -=obj.Mul ;
            md(450,50);
            Console .ReadLine ();
            
        }

    }
}

Delegates in C#

It is also an user defined type which is used for invoking or calling the methods of a class.

A method that is defined under a class can be called in 2 different ways

• With the help of object of a class if it is non static or name of a class if it is static.
• By using the delegate also we can call  the method of a class even if it is static or non static.

Note: Calling the method in the 1st process is different than calling the method in the 2nd process.

Calling a method using a Delegate

       If we want to call a method using a delegate we need to adopt the following process

• Defining a delegate:   

[<modifiers>] delegate <void/type> <Name> ([<Parameter Definition's>])

The definition of a delegate is similar to a method definition where a method will have body whereas a delegate will not have any body where we use these delegates for calling these methods.

Note: While defining a delegate make sure the I/O parameters of Delegates are same as the I/O parameters of the method we want to call with the help of a delegate.

• As the delegate is a type, after defining a delegate to consume it we need to create an object of it and while creating the object, the method we want to call using the delegate should be passed as a parameter to the delegates constructor.

• Now call the delegate by passing the required parameter value so that the method gets executed internally.

Delegate Example

using System;
namespace CSharpConsole
{
    class DelDemo
    {
        public void Add(int x, int y)
        {
            Console.WriteLine(x + y);
        }
        public static string SayHello(string name)
        {
            return "Hello " + name;
        }
        public delegate void AddDel(int a, int b);
        public delegate string SayDel(string name);

        static void Main()
        {
            DelDemo obj = new DelDemo();
            AddDel ad = new AddDel(obj.Add);
            SayDel  sd = new SayDel (DelDemo.SayHello);
            ad(100, 50); ad(234, 434); ad(672, 157);
            Console.WriteLine(sd("AAA"));
            Console.WriteLine(sd("BBB"));
            Console.WriteLine(sd("CCC"));
            Console.ReadLine();
                   
        }
    }
}