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.NET interview questions: -Elaborate the term Volatile Keyword?

By Shiv Prasad Koirala in ASP.NET
Oct 4th, 2011
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Volatile Keyword: - The Volatile keyword ensures that whichever the variable data you are accessing currently is up to date or is sinking with main memory which is being updated.

In other words you will use Volatile Keyword in scenarios when you are doing multi-threading applications and especially when you are accessing data which is being updated concurrently by multiple threads.

Now, let's see a scenario where the actual use of the Volatile Keyword exists.

In order to see it practically and understand the concept and the use of the Volatile Keyword just follow the following steps.

Step1: - create a simple Console Application for that just go to >> File >> New >> Project >> Windows >> Select Console Application.

Step2: - Import the below Namespace.

using System.Threading;

Step3: - Now, just simply add the below code snippet in to yourProgram.cs file of Console Application.

class Program

private bool _loop = true;
static void Main(string[] args)

//Calling the SomeThread method in
//MultiThreaded Manner.
Program test1 = new Program();
Thread obj = new Thread(SomeThread);
obj.Start(test1);
//Pauses for 20 ms
Thread.Sleep(20);
//Setting the loop value to false.
test1._loop = false;
Console.WriteLine("Step2 :- The Value is Set To False");
}
//Simple Method called SomeThread.
private static void SomeThread(object o1)

Program o = (Program)o1;
Console.WriteLine("Step1 :- Entered The Loop");
//This will run untill the _loop value is true.
while (o._loop)
 
}
Console.WriteLine("Step3 :- Exited The Loop");
Console.ReadLine();
}

Let me just explain flow of the program, when you execute your program first the below code line will get executed.

Program test1 = new Program();
Thread obj = new Thread(SomeThread);
obj.Start(test1);
Thread.Sleep(20);

Once the above line of thread is executed it should display us the below code of line which is inside the SomeThread Method.

Program o = (Program)o1;
Console.WriteLine("Step1 :- Entered The Loop");

Now the below while loop will run continuously until the _loop value is set to false.

while (o._loop)
 
}

Now, the below line of code will get executed and the value of the _loop will be set to false.

test1._loop = false;
Console.WriteLine("Step2 :- The Value is Set To False");

Once the value of the _loop is set to false, now the while loop will get terminated and the below line of code will get executed.

Console.WriteLine("Step3 :- Exited The Loop");

Step4: - now, just run the Console Application and you will see the result like below diagram.

Note: - Please run your application in Release mode.

In the above diagram of output you can clearly see that the step3 has not been executed.

Step5: - Now, just make necessary changes to the program.cs file like below code snippet.

class Program

private volatile bool _loop = true;
static void Main(string[] args)

//Calling the SomeThread method in
//MultiThreaded Manner.
Program test1 = new Program();
Thread obj = new Thread(SomeThread);
obj.Start(test1);
//Pauses for 20 ms
Thread.Sleep(20);
//Setting the loop value to false.
test1._loop = false;
Console.WriteLine("Step2 :- The Value is Set To False");
}
//Simple Method called SomeThread.
private static void SomeThread(object o1)

Program o = (Program)o1;
Console.WriteLine("Step1 :- Entered The Loop");
//This will run untill the _loop value is true.
while (o._loop)
 
}
Console.WriteLine("Step3 :- Exited The Loop");
Console.ReadLine();
}

Now, just your application and will find result like below diagram.

Also see the following video on volatile keyword in C# and .NET: -