Exit the loop after specific time in C#

Question

I have a requirement in my project (C#, VS2010, .NET 4.0) that a particular for loop must finish within 200 milliseconds. If it doesn't then it has to terminate after this duration without executing the remaining iterations. The loop generally goes for i = 0 to about 500,000 to 700,000 so the total loop time varies.

I have read following questions which are similar but they didn't help in my case:

1. What is the best way to exit out of a loop after an elapsed time of 30ms in C++
2. How to execute the loop for specific time

So far I have tried using a Stopwatch object to track the elapsed time but it's not working for me. Here are 2 different methods I have tried so far:

Method 1. Comparing the elapsed time within for loop:

Stopwatch sw = new Stopwatch();
sw.Start();

for (i = 0; i < nEntries; i++) // nEntries is typically more than 500,000
{
      // Do some stuff
      ...
      ...
      ...

      if (sw.Elapsed > TimeSpan.FromMilliseconds(200))
          break;
}

sw.Stop();

This doesn't work because if (sw.Elapsed > TimeSpan.FromMilliseconds(200)) takes more than 200 milliseconds to complete. Hence useless in my case. I am not sure whether TimeSpan.FromMilliseconds() generally takes this long or it's just in my case for some reason.

Method 2. Creating a separate thread to compare time:

Stopwatch sw = new Stopwatch();
sw.Start();                    
bool bDoExit = false;
int msLimit = 200;

System.Threading.ThreadPool.QueueUserWorkItem((x) =>
{
     while (bDoExit == false)
     {
        if (sw.Elapsed.Milliseconds > msLimit)
        {
            bDoExit = true;
            sw.Stop();
         }

         System.Threading.Thread.Sleep(10);
      }

});

for (i = 0; i < nEntries; i++) // nEntries is typically more than 500,000
{
      // Do some stuff
      ...
      ...
      ...

      if (bDoExit == true)
          break;
}

sw.Stop();

I have some other code in the for loop that prints some statistics. It tells me that in case of Method 2, the for loop definitely breaks before completing all the iterations but the loop timing is still 280-300 milliseconds.

Any suggestions to break a for loop strictly with-in 200 milliseconds or less? Thanks.

Answer 1

Another option would be to use CancellationTokenSource:

CancellationTokenSource source = new CancellationTokenSource(100);

while(!source.IsCancellationRequested)
{
    // Do stuff
}

Answer 2

Using cancellation token:

 var cancellationToken = new CancellationTokenSource(TimeSpan.FromSeconds(15)).Token;

 while (!cancellationToken.IsCancellationRequested)
 {
     //Do stuff...
 }