Simple C# concurrency / multithreading

Simple C# concurrency / multithreading

I'm probably missing something basic here, but still would appreciate your
kind help in understanding this. So I have the following simple
multithreaded program I wrote:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
// List<int> outcome = new List<int>();
Test t = new Test();
Thread thread1 = new Thread(new ThreadStart(t.call1));
Thread thread2 = new Thread(new ThreadStart(t.call2));
thread1.Start();
thread2.Start();
Thread.Sleep(3000); //Give enough time for threads to end
Console.Write("{0},", t.mSum);
t.mSum = 0;
}
}
class Test
{
public int mSum = 0;
public void call1()
{
//lock (this)
//{
for (int i = 0; i < 100; i++)
{
Console.WriteLine("Hello Thread 1, mSum value: {0}", mSum);
mSum = mSum + 1;
Console.WriteLine("Goodbye Thread 1, mSum value: {0}", mSum);
}
//}
// Console.WriteLine(mSum);
}
public void call2()
{
for (int i = 0; i < 100 ; i++)
{
Console.WriteLine("Hello Thread 2, mSum value: {0}",mSum);
mSum = mSum + 1;
Console.WriteLine("Goodbye Thread 2, mSum value: {0}",mSum);
}
}
}
}
So I would expect this output to be nondetermenistic because context
switching can occur anytime right? But when I run the program, I get the
following output (only a part of the output, malformed due to my poor
stackoverflow.com question posting skills):
Hello Thread 1, mSum value: 62 Goodbye Thread 1, mSum value: 63
Hello Thread 1, mSum value: 63 Goodbye Thread 1, mSum value: 64
Hello Thread 2, mSum value: 59 Goodbye Thread 2, mSum value: 65
Hello Thread 2, mSum value: 65 Goodbye Thread 2, mSum value: 66
So, assuming I wrote this right, and mSum is indeed shared between the
threads (looks like it...) - how can I explain line no. 3? Thread 2 reads
59, adds 1 and then we get 65!
Did I discover a new kind of math? :)
Thanks in advance.