C# Online Compiler | .NET Fiddle

using System;
using System.Threading;
using System.Threading.Tasks;
					
public class Program
{
	public static void Main()
	{
		Console.WriteLine("--- started ---");
		/*initialization is thread safe*/
		MyClass.MyClassInstance.Value.SomeFunction();
		MyClass.MyClassInstance.Value.SomeFunction();
		MyClass.MyClassInstance.Value.SomeFunction();
		
		//first batch with no locking
		/*After initilization , function calls are not thread safe. Response from below 3 tasks WILL NOT guarantee 1,2 and 3 response.*/
		Task task1 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(1);});
		Task task2 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(2);});
		Task task3 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(3);});
		
		//second batch with locking
		/*The object needs to be locked, to be thread safe. Response from below 3 tasks WILL guarantee 1,2 and 3 response.*/
		Task task4 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetValWithLock(1);});
		Task task5 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetValWithLock(2);});
		Task task6 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetValWithLock(3);});
	}
	
	public class MyClass{
		public static Lazy<MyClass> MyClassInstance = new Lazy<MyClass>(()=> new MyClass());
		public int val1 {get;set;}
		public int val2 {get;set;}
		
		private MyClass(){
			Console.WriteLine("instance created");
		}
		
		public void SomeFunction(){
			Console.WriteLine("inside some function");
		}
		
		public void SetVal(int i){
			val1 = i;
			Console.WriteLine(val1);
		}
		
		public void SetValWithLock(int i){
			
			lock(MyClassInstance.Value)
        	{
				val2 = i;
				Console.WriteLine(val2);
			}
		}
	}
	
}

 
using System;
using System.Threading;
using System.Threading.Tasks;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("--- started ---");
        /*initialization is thread safe*/
        MyClass.MyClassInstance.Value.SomeFunction();
        MyClass.MyClassInstance.Value.SomeFunction();
        MyClass.MyClassInstance.Value.SomeFunction();
        
        //first batch with no locking
        /*After initilization , function calls are not thread safe. Response from below 3 tasks WILL NOT guarantee 1,2 and 3 response.*/
        Task task1 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(1);});
        Task task2 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(2);});
        Task task3 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetVal(3);});
        
        //second batch with locking
        /*The object needs to be locked, to be thread safe. Response from below 3 tasks WILL guarantee 1,2 and 3 response.*/
        Task task4 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetValWithLock(1);});
        Task task5 = Task.Factory.StartNew(()=>{MyClass.MyClassInstance.Value.SetValWithLock(2);});