Why such a short run time? - asynchronous

Question

I implemented a solution to the dining philosophers problem in C# (some time ago, can't remember when, can't remember where) and I recently reopened it and added some timing output. The test appears to run for only a few milliseconds when the actual test run takes many, many seconds. In fact, I can force it to run for minutes, though the test still shows less than 500 milliseconds.
In short, I'm creating a collection of Tasks, having them run (on and off) for a few seconds each, looping in the main execution until they complete and writing out the difference between the start and end time.
Here is the NUnit unit test being used to run the solution:
[Test]
public void DoesEveryOneEat_WaitsForAllToFinish()
{
// arrange
var start = DateTime.Now;
// act
foreach (var philosopher in Thinkers)
{
philosopher.StartEating();
}
// wait
bool someoneIsHungry = true;
while (someoneIsHungry)
{
someoneIsHungry = false;
foreach (var philosopher in Thinkers)
{
if (!someoneIsHungry && philosopher.IsHungry)
someoneIsHungry = true;
}
}
Console.WriteLine(DateTime.Now.Subtract(start).Milliseconds);
// assert
Assert.AreEqual(false, Thinkers[0].IsHungry, "Philosopher 0 is hungry and ate for only " + Thinkers[0].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[1].IsHungry, "Philosopher 1 is hungry and ate for only " + Thinkers[1].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[2].IsHungry, "Philosopher 2 is hungry and ate for only " + Thinkers[2].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[3].IsHungry, "Philosopher 3 is hungry and ate for only " + Thinkers[3].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[4].IsHungry, "Philosopher 4 is hungry and ate for only " + Thinkers[4].AteForMillis + " milliseconds.");
}
philosopher.StartEating(); starts a task which runs until a satisfactory outcome has arrived and then exits:
public async void StartEating()
{
await Task.Factory.StartNew(Run);
}
public void Run()
{
while (_totalRunTime < MaxEatMillis)
{
if (Monitor.TryEnter(Left))
{
if (Monitor.TryEnter(Right))
{
Eat();
Monitor.Exit(Right);
}
Monitor.Exit(Left);
}
}
}
While I would welcome constructive comments on this code, my question is: Why does the unit test console output only 582 milliseconds when the test itself does not complete for easily 9 seconds or more?
(I would surmise that this is because the time taken for the actual unit test code to run is only 582 milliseconds but that the NUnit library is not allowing the assertions to run until all tasks started by the test to complete. However, this does not vibe in my head properly, as if writing code which would rely on that fact would fail.)
Full listing:
public class ChopStick
{
public int Index { get; set; }
}
public class Philosopher
{
protected ChopStick Left { get; set; }
protected ChopStick Right { get; set; }
private int _totalRunTime = 0;
private readonly int MaxEatMillis = 3000;
private readonly int MaxRunMillis = 1000;
public Philosopher(ChopStick left, ChopStick right)
{
Left = left;
Right = right;
}
public async void StartEating()
{
await Task.Factory.StartNew(Run);
}
public void Run()
{
while (_totalRunTime < MaxEatMillis)
{
if (Monitor.TryEnter(Left))
{
if (Monitor.TryEnter(Right))
{
Eat();
Monitor.Exit(Right);
}
Monitor.Exit(Left);
}
}
}
private void Eat()
{
var eatTime = new Random().Next(1, MaxRunMillis);
Thread.Sleep(eatTime);
_totalRunTime += eatTime;
}
public bool IsHungry => _totalRunTime < MaxEatMillis;
public int AteForMillis => _totalRunTime;
}
[Test]
public void DoesEveryOneEat_WaitsForAllToFinish()
{
// arrange
var start = DateTime.Now;
Console.WriteLine(DateTime.Now.Subtract(start).Milliseconds);
// act
foreach (var philosopher in Thinkers)
{
philosopher.StartEating();
}
// wait
bool someoneIsHungry = true;
while (someoneIsHungry)
{
someoneIsHungry = false;
foreach (var philosopher in Thinkers)
{
if (!someoneIsHungry && philosopher.IsHungry)
someoneIsHungry = true;
}
}
Console.WriteLine(DateTime.Now.Subtract(start).Milliseconds);
// assert
Assert.AreEqual(false, Thinkers[0].IsHungry, "Philosopher 0 is hungry and ate for only " + Thinkers[0].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[1].IsHungry, "Philosopher 1 is hungry and ate for only " + Thinkers[1].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[2].IsHungry, "Philosopher 2 is hungry and ate for only " + Thinkers[2].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[3].IsHungry, "Philosopher 3 is hungry and ate for only " + Thinkers[3].AteForMillis + " milliseconds.");
Assert.AreEqual(false, Thinkers[4].IsHungry, "Philosopher 4 is hungry and ate for only " + Thinkers[4].AteForMillis + " milliseconds.");
Console.WriteLine(DateTime.Now.Subtract(start).Milliseconds);
}

Answer 1

In your timing code, you should use TotalMilliseconds rather than Milliseconds.
Or just output the TimeSpan directly:
Console.WriteLine(DateTime.Now.Subtract(start));
As a side note, Stopwatch is generally used for timings rather than DateTime.Now.