public void WillNotDriftTooFarFromUtcNow()
{
ITimestampSource target = new PseudoHighResTimestampSource();
const int MAX_DRIFT_MS = 10;
// Average over 10000 iterations and get the average drift
decimal totalDrift = 0;
const int iterations = 10000;
for (int i = 0; i < iterations; i++)
{
DateTime current = DateTime.UtcNow;
DateTime result = target.GetUtcNow();
totalDrift += Convert.ToDecimal((result - current).TotalMilliseconds);
}
Decimal averageDrift = totalDrift / iterations;
if (averageDrift > MAX_DRIFT_MS)
{
output.WriteLine($"Expected times were more than {MAX_DRIFT_MS}ms apart. Instead they were {averageDrift}ms apart.");
Assert.True(false); // Force fail.
}
else
{
output.WriteLine($"Total Drift over {iterations} iterations: {totalDrift}ms. Average {averageDrift}ms");
}
}
public void WillGiveUtcDateTimeKind()
{
ITimestampSource target = new PseudoHighResTimestampSource();
DateTime result = target.GetUtcNow();
Assert.Equal(DateTimeKind.Utc, result.Kind);
}
public void CanSupplyHighResTimestamps()
{
const int iterations = 100000;
// Even if we call inside a very tight loop,
// we should get better (pseudo) resolution than just DateTime.UtcNow
long dateTimeCollisions = 0;
DateTime previousDateTime = DateTime.UtcNow;
for (int i = 0; i < iterations; i++)
{
// Attempt with date time directly
DateTime current = DateTime.UtcNow;
if (previousDateTime == current)
{
dateTimeCollisions++;
}
previousDateTime = current;
}
if (0 == dateTimeCollisions)
{
// Warn because we do expect that datetime.now has collisions in such a tight loop
output.WriteLine("Warning! Expected DateTime.UtcNow to have some collisions, but seemed to be high resolution already.");
}
// Now attempt to use our pseudo high precision provider that includes a sequence number to ensure that it
// never collides
ITimestampSource target = new PseudoHighResTimestampSource();
long highResTotalCollisions = 0;
previousDateTime = target.GetUtcNow();
for (int i = 0; i < iterations; i++)
{
// Attempt with date time directly
DateTime current = target.GetUtcNow();
if (previousDateTime == current)
{
highResTotalCollisions++;
}
previousDateTime = current;
}
Assert.Equal(0, highResTotalCollisions);
output.WriteLine($"No collisions detected with high resolution source, compared to {dateTimeCollisions} for DateTime.UtcNow.");
}
