Why Task canceled run again with new Task? - task-parallel-library

Question

I have a example about Task. I start a new Task to do a LongTask and after I cancel the Task and after start a new Task to do a LongTask again. But the TaskA is run not normally. It run the work of Task canceled and new Task.
How to run a new Task immediately and the Task canceled don't run again ?
Here my codes:
class Program
{
private static CancellationTokenSource tokenSource = new CancellationTokenSource();
static void Main(string[] args)
{
Program a = new Program();
Task.Factory.StartNew(() => a.LongTask(), tokenSource.Token);
Console.ReadLine();
//After enter
tokenSource.Cancel();
//Create new CancellationTokenSource to make Task continue run
tokenSource = new CancellationTokenSource();
Task.Factory.StartNew(() => a.LongTask(), tokenSource.Token);
Console.ReadLine();
}
public void LongTask()
{
StringBuilder display = new StringBuilder();
while (!tokenSource.IsCancellationRequested)
{
display.Append("1");
Console.WriteLine(display);
Thread.Sleep(1000);
}
}
}

Answer 1

I will visualize what happens when the first task is sleeping
while (!tokenSource.IsCancellationRequested)
{
display.Append("1");
Console.WriteLine(display);
Thread.Sleep(1000);
// tokenSource.Cancel();
// tokenSource = new CancellationTokenSource();
// Task.Factory.StartNew second task
}
then after sleeping timeout, task #1 continues its loop to check tokenSource.IsCancellationRequested which is false (because this token is the new one).
Now you understand why two tasks are running that way. Let's try my code:
static void Main(string[] args)
{
var a = new Program();
var token = new CancellationTokenSource();
Task t1 = Task.Factory.StartNew(() => a.LongTask("#1", token1.Token), token1.Token);
Console.ReadLine();
token1.Cancel();
token = new CancellationTokenSource();
Task.Factory.StartNew(() => a.LongTask("#2", token2.Token), token2.Token);
Console.ReadLine();
}
public void LongTask(string name, CancellationToken killer)
{
var display = new StringBuilder();
while (!killer.IsCancellationRequested)
{
display.Append("1");
Console.WriteLine("{0} says: {1}",name, display);
Thread.Sleep(1000);
}
}
The trick here is to give each task a different token other than share same static token instance.