I am making an XNA game and it's time to make daytime system and for that I need some kind of clock. I tried to use GameTime.TotalGameTime.Milliseconds == 0 to add one second to the second counter of my custom clock class, but it turned out that GameTime doesn't always run through zero milliseconds. Using TimeSpan prevUpdate to compare to TotalGameTime.TotalSeconds doesn't give enough precision, and the time is noticeably slower than the real time somehow.
What XNA or .Net component can I use to base my clock on so that it doesn't cost too much resources or deviates noticeably from real time?
Use Stopwatch for high-precision timing (reference).
Use XNA's GameTime for rendering and frame-to-frame timing logic. XNA's timer does not match "wall clock" time exactly. It is able to drift in order to better line up with frame rendering, giving you smoother animation (this is behaviour is provided by the Game class). Over time it will deviate from real time slightly, but for most games this is not a problem.
Use DateTime for measuring longer time spans accurately (eg: minutes, hours).
Note that you shouldn't compare Milliseconds == 0, because you cannot know exactly when XNA will call your Update method, so you could have Milliseconds == 999 on one frame, and then Milliseconds == 15 the next - wrapping around and skipping past 0, so your condition never triggers.
So you need to determine when the timer crosses the threshold. There are many ways to do this. You could track a threshold (useful if you are tracking some "total" time), incrementing it after each trigger. Personally I prefer to accumulate time like so:
seconds += gameTime.ElapsedTime.TotalSeconds;
if(seconds > 1.0)
{
seconds -= 1.0;
DoSomething(); // Triggered each second
}
What should be the best way to calculate the time diff which is accurate upto the level of Microseconds. currently I am doing as follows:
((TimeSpan)(DateTime.Now - _perfClock)).TotalMilliseconds
Note: perfClock is DateTime (set prior to task)
Which is suppose to give accuracy upto Milliseconds, but in my case it is showing values ends with "000". like 8000,9000 etc...
This is forcing me to think that is just converting seconds to Milliseconds somewhere, instead of calculating diff in Milliseconds. (Possibly I am wrong somewhere in code above).
But what should be the recommended mechanism for accurate Time Diff calculation?
-Sumeet
The issue is not with TimeSpan, that is accurate down to ticks, which is 100 nanoseconds.
The issue is you are using DateTime.Now for your timer.
DateTime.Now is accurate to about 16ms i believe. as mentioned by V4Vendetta, you want to use Stopwatch if you need "high resolution" results. Stopwatch can provide you with ticks (long) or TimeSpan. use Timespan for easy manipulation (in your case, add/subtract).
Note also that Stopwatch provides a .IsHighResolution property, to see if you have a better accuracy than Datetime.Now (it's always true on PC iirc)
I don't know the context in which you are measuring time but it would be good to start of with Stopwatch and check your results.
Also worth a read Precise Measurement
Have you tried:
TimeSpan diff = DateTime.Now.Subtract(_perfClock);
In C++ I am able to get the current time when my application starts I can use
time_t appStartTime = time(null);
then to find the difference in seconds from when it started I can just do the same thing, then find the difference. It looks like I should be using "System.DateTime" in C# net, but the MSDN is confusing in its explanation.
How can I use System.DateTime to find the difference in time (in seconds) between when my application starts, and the current time?
Use Now property
DateTime startTime = DateTime.Now;
//work
DateTime currentTime = DateTime.Now;
and then just simply calculate the difference.
currentTime - startTime;
If you would like to measure the performance consider using Stopwatch.
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
//work
stopWatch.Stop();
As everyone suggested... But they were a little wrong :-) Use DateTime.UtcNow, because
It's faster (DateTime.Now calls DateTime.UtcNow)
It works around change of DST on/off.
OR
As #Shekhar_Pro suggested (yes, he was right!), use the Stopwatch
var sw = Stopwatch.StartNew()
.... your code
sw.Stop();
var ms = sw.ElapsedMilliseconds;
or
var ticks = sw.ElapsedTicks;
Oh... and I was forgetting... What you are doing is probably worthless in certain situation... You know, 2011 processors are multicore (and even 2010 :-) )... If you app is vaguely multithread you are probably better measuring:
Process.GetCurrentProcess().TotalProcessorTime
This include the use of all the cores used by your app... So on a dual core, using both cores, it will "gain" 2 seconds for every "real time" second.
If you are using this for checking performance and time taken to Execute code then you Best bet is to use StopWatch.
otherwise System.DateTime has a Subtract function which can be used to get a TimeSpan object or even a simple - (subtract) operator will do it.
Then that TimeSpan object has a property of TotalSeconds which you can use.
Several ways to do this:
Use DateTime.Now. Subtracting produces a TimeSpan. Takes 8 bytes of storage, times up to 8000 years, resolution of 1 millisecond but accurate to 1/64 second on most machines.
Use Environment.TickCount. Similar to time_t but relative from machine boot time. Takes 4 bytes of storage, times up to 24 days (49 with a cast), resolution and accuracy same as DateTime.
Use Stopwatch. Stored on the heap, resolution is machine dependent but almost always well below a microsecond. Accuracy isn't usually good but repeats decently, assume +/- 5%. Best used to measure small intervals for comparison.
Use timeGetTime. This requires pinvoke to use this multimedia timer. Similar to Environment.TickCount, you can get 1 msec accuracy by using timeBeginPeriod. This is not cheap since it has system-wide effects. Best avoided.
Keep in mind that process execution is subject to the vagaries of overall operating system load, your program is sharing resources with the other 70-odd processes that are running. Either DateTime or TickCount has plenty of accuracy for that.
DateTime startTime = DateTime.Now;
//some code
TimeSpan difference = DateTime.Now - startTime;
int seconds = difference.TotalSeconds.Truncate();
I need to format the day time using QueryPerformanceCounter Win32 API.
The format, is: HH:mm:ss.ffffff , containing hours minuts seconds and microseconds.
I need to use THIS function, because another process (written in C) is using this function and the purpose is using the same function in both places.
Thanks
The System.Diagnostics.Stopwatch class uses QueryPerformanceCounter(), saves you from having to P/Invoke it.
You should not use QueryPerformanceCounter to determine time of day. It can only be used to determine an elapsed interval with a very high resolution as it returns the number of ticks that passed since the computer was last restarted.
As such, at best, you may only determine how many hours, minutes, and seconds have passed since a previous reading of QueryPerformanceCounter which must not have happened too long in the past.
In order to convert from ticks to seconds you need to determine the frequency (using QueryPerformanceFrequency) of the ticks on the computer you're running the QueryPerformanceCounter function and then divide your reading by that frequency:
// obtain frequency
long freq;
QueryPerformanceFrequency(freq);
// then obtain your first reading
long start_count;
long end_count;
QueryPerformanceCounter(start_count)
// .. do some work
// obatin your second reading
QueryPerformanceCounter(end_count);
// calculate time elapsed
long milliseconds_elapsed = (long)(((double)(end_count - start_count) / freq) * 1000);
// from here on you can format milliseconds_elapsed any way you need to
An alternative to the above example would be to use the TimeSpan structure available in .Net which has a constructor that takes ticks like so:
// then obtain your first reading
long start_count;
long end_count;
QueryPerformanceCounter(start_count)
// .. do some work
// obatin your second reading
QueryPerformanceCounter(end_count);
TimeSpan time_elapsed = new TimeSpan(end_count - start_count);
Console.WriteLine("Time Elapsed: " + time_elapsed.ToString());
Can use :
1) The System.Diagnostics.Stopwatch class uses QueryPerformanceCounter(), saves you from having to P/Invoke it.
2) Can use directly by importing from the Win32 dll . [DLLImport(Win32)] and the name ofthe function
Possibly I misunderstand the question, as for me none of the previous answers are relevant at all.
I had the problem (which sent me here): Given a value from QueryPerformanceCounter, because something out of my control specifies timestamps using that function, how can I convert these values to a normal date / time?
I figured that QueryPerformanceCounter returns the number of seconds since the system booted, multiplied (and extended in resolution) depending on QueryPerformanceFrequency.
Thus, the most simple solution is to get the current date/time, subtract the amount of seconds returned by QueryPerformanceCounter/QueryPerformanceFrequency, and then add the values you like to format as time of day.
Up until now I used DateTime.Now for getting timestamps, but I noticed that if you print DateTime.Now in a loop you will see that it increments in descrete jumps of approx. 15 ms. But for certain scenarios in my application I need to get the most accurate timestamp possible, preferably with tick (=100 ns) precision. Any ideas?
Update:
Apparently, StopWatch / QueryPerformanceCounter is the way to go, but it can only be used to measure time, so I was thinking about calling DateTime.Now when the application starts up and then just have StopWatch run and then just add the elapsed time from StopWatch to the initial value returned from DateTime.Now. At least that should give me accurate relative timestamps, right? What do you think about that (hack)?
NOTE:
StopWatch.ElapsedTicks is different from StopWatch.Elapsed.Ticks! I used the former assuming 1 tick = 100 ns, but in this case 1 tick = 1 / StopWatch.Frequency. So to get ticks equivalent to DateTime use StopWatch.Elapsed.Ticks. I just learned this the hard way.
NOTE 2:
Using the StopWatch approach, I noticed it gets out of sync with the real time. After about 10 hours, it was ahead by 5 seconds. So I guess one would have to resync it every X or so where X could be 1 hour, 30 min, 15 min, etc. I am not sure what the optimal timespan for resyncing would be since every resync will change the offset which can be up to 20 ms.
The value of the system clock that DateTime.Now reads is only updated every 15 ms or so (or 10 ms on some systems), which is why the times are quantized around those intervals. There is an additional quantization effect that results from the fact that your code is running in a multithreaded OS, and thus there are stretches where your application is not "alive" and is thus not measuring the real current time.
Since you're looking for an ultra-accurate time stamp value (as opposed to just timing an arbitrary duration), the Stopwatch class by itself will not do what you need. I think you would have to do this yourself with a sort of DateTime/Stopwatch hybrid. When your application starts, you would store the current DateTime.UtcNow value (i.e. the crude-resolution time when your application starts) and then also start a Stopwatch object, like this:
DateTime _starttime = DateTime.UtcNow;
Stopwatch _stopwatch = Stopwatch.StartNew();
Then, whenever you need a high-resolution DateTime value, you would get it like this:
DateTime highresDT = _starttime.AddTicks(_stopwatch.Elapsed.Ticks);
You also may want to periodically reset _starttime and _stopwatch, to keep the resulting time from getting too far out of sync with the system time (although I'm not sure this would actually happen, and it would take a long time to happen anyway).
Update: since it appears that Stopwatch does get out of sync with the system time (by as much as half a second per hour), I think it makes sense to reset the hybrid DateTime class based on the amount of time that passes between calls to check the time:
public class HiResDateTime
{
private static DateTime _startTime;
private static Stopwatch _stopWatch = null;
private static TimeSpan _maxIdle =
TimeSpan.FromSeconds(10);
public static DateTime UtcNow
{
get
{
if ((_stopWatch == null) ||
(_startTime.Add(_maxIdle) < DateTime.UtcNow))
{
Reset();
}
return _startTime.AddTicks(_stopWatch.Elapsed.Ticks);
}
}
private static void Reset()
{
_startTime = DateTime.UtcNow;
_stopWatch = Stopwatch.StartNew();
}
}
If you reset the hybrid timer at some regular interval (say every hour or something), you run the risk of setting the time back before the last read time, kind of like a miniature Daylight Savings Time problem.
To get a high-resolution tick-count, please, use the static Stopwatch.GetTimestamp()-method:
long tickCount = System.Diagnostics.Stopwatch.GetTimestamp();
DateTime highResDateTime = new DateTime(tickCount);
just take a look at the .NET Source Code:
public static long GetTimestamp() {
if(IsHighResolution) {
long timestamp = 0;
SafeNativeMethods.QueryPerformanceCounter(out timestamp);
return timestamp;
}
else {
return DateTime.UtcNow.Ticks;
}
}
Source Code here: http://referencesource.microsoft.com/#System/services/monitoring/system/diagnosticts/Stopwatch.cs,69c6c3137e12dab4
[The accepted answer does not appear to be thread safe, and by its own admission can go backwards in time causing duplicate timestamps, hence this alternative answer]
If what you really care about (per your comment) is in fact, a unique timestamp that is allocated in strict ascending order and which corresponds as closely as possible to the system time, you could try this alternative approach:
public class HiResDateTime
{
private static long lastTimeStamp = DateTime.UtcNow.Ticks;
public static long UtcNowTicks
{
get
{
long orig, newval;
do
{
orig = lastTimeStamp;
long now = DateTime.UtcNow.Ticks;
newval = Math.Max(now, orig + 1);
} while (Interlocked.CompareExchange
(ref lastTimeStamp, newval, orig) != orig);
return newval;
}
}
}
These suggestions all look too hard! If you're on Windows 8 or Server 2012 or higher, use GetSystemTimePreciseAsFileTime as follows:
[DllImport("Kernel32.dll", CallingConvention = CallingConvention.Winapi)]
static extern void GetSystemTimePreciseAsFileTime(out long filetime);
public DateTimeOffset GetNow()
{
long fileTime;
GetSystemTimePreciseAsFileTime(out fileTime);
return DateTimeOffset.FromFileTime(fileTime);
}
This has much, much better accuracy than DateTime.Now without any effort.
See MSDN for more info: http://msdn.microsoft.com/en-us/library/windows/desktop/hh706895(v=vs.85).aspx
It does return the most accurate date and time known to the operating system.
The operating system also provides higher resolution timing through QueryPerformanceCounter and QueryPerformanceFrequency (.NET Stopwatch class). These let you time an interval but do not give you date and time of day. You might argue that these would be able to give you a very accurate time and day, but I am not sure how badly they skew over a long interval.
1). If you need high resolution absolute accuracy: you can't use DateTime.Now
when it is based on a clock with a 15 ms interval (unless it
is possible "slide" the phase).
Instead, an external source of better resolution absolute
accuracy time (e.g. ntp), t1 below, could be combined with the high
resolution timer (StopWatch / QueryPerformanceCounter).
2). If you just need high resolution:
Sample DateTime.Now (t1) once together with a value from the
high resolution timer (StopWatch / QueryPerformanceCounter)
(tt0).
If the current value of the high resolution timer is tt then the
current time, t, is:
t = t1 + (tt - tt0)
3). An alternative could be to disentangle absolute time and
order of the financial events: one value for absolute time
(15 ms resolution, possibly off by several minutes) and one
value for the order (for example, incrementing a value by one each
time and store that). The start value for the order can be
based on some system global value or be derived from the
absolute time when the application starts.
This solution would be more robust as it is not dependent on
the underlying hardware implementation of the clocks/timers
(that may vary betweens systems).
This is too much work for something so simple. Just insert a DateTime in your database with the trade. Then to obtain trade order use your identity column which should be an incrementing value.
If you are inserting into multiple databases and trying to reconcile after the fact then you will be mis-calculating trade order due to any slight variance in your database times (even ns increments as you said)
To solve the multiple database issue you could expose a single service that each trade hits to get an order. The service could return a DateTime.UtcNow.Ticks and an incrementing trade number.
Even using one of the solutions above anyone conducting trades from a location on the network with more latency could possibly place trades first (real world), but they get entered in the wrong order due to latency. Because of this the trade must be considered placed at the database, not at users' consoles.
The 15 ms (actually it can be 15-25 ms) accuracy is based on the Windows 55 Hz/65 Hz timer resolution. This is also the basic TimeSlice period. Affected are Windows.Forms.Timer, Threading.Thread.Sleep, Threading.Timer, etc.
To get accurate intervals you should use the Stopwatch class. It will use high-resolution if available. Try the following statements to find out:
Console.WriteLine("H = {0}", System.Diagnostics.Stopwatch.IsHighResolution);
Console.WriteLine("F = {0}", System.Diagnostics.Stopwatch.Frequency);
Console.WriteLine("R = {0}", 1.0 /System.Diagnostics.Stopwatch.Frequency);
I get R=6E-08 sec, or 60 ns. It should suffice for your purpose.
I'd add the following regarding MusiGenesis Answer for the re-sync timing.
Meaning: What time should I use to re-sync ( the _maxIdle in MusiGenesis answer's)
You know that with this solution you are not perfectly accurate, thats why you re-sync.
But also what you implicitly want is the same thing as Ian Mercer solution's:
a unique timestamp that is allocated in strict ascending order
Therefore the amount of time between two re-sync ( _maxIdle Lets call it SyncTime) should be function of 4 things:
the DateTime.UtcNow resolution
the ratio of accuracy you want
the precision level you want
An estimation of the out-of-sync ratio of your machine
Obviously the first constraint on this variable would be :
out-of-sync ratio <= accuracy ratio
For example : I dont want my accuracy to be worst than 0.5s/hrs or 1ms/day etc... (in bad English: I dont want to be more wrong than 0.5s/hrs=12s/day).
So you cannot achieve a better accuracy than what the Stopwatch offer you on your PC. It depends on your out-of-sync ratio, which might not be constant.
Another constraint is the minimum time between two resync:
Synctime >= DateTime.UtcNow resolution
Here accuracy and precision are linked because if you using a high precision (for example to store in a DB) but a lower accuracy, You might break Ian Mercer statement that is the strict ascending order.
Note: It seems DateTime.UtcNow may have a bigger default Res than 15ms (1ms on my machine) Follow the link:
High accuracy DateTime.UtcNow
Let's take an example:
Imagine the out-of-sync ratio commented above.
After about 10 hours, it was ahead by 5 seconds.
Say I want a microsec precision. My timer res is 1ms (see above Note)
So point by point:
the DateTime.UtcNow resolution : 1ms
accuracy ratio >= out-of-sync ratio,
lets take the most accurate possible so : accuracy ratio = out-of-sync ratio
the precision level you want : 1 microsec
An estimation of the out-of-sync ratio of your machine : 0.5s/hour (this is also my accuracy)
If you reset every 10s, imagine your at 9.999s, 1ms before reset.
Here you make a call during this interval. The time your function will plot is ahead by : 0.5/3600*9.999s eq 1.39ms.
You would display a time of 10.000390sec. After UtcNow tick, if you make a call within the 390micro sec, your will have a number inferior to the previous one. Its worse if this out-of-sync ratio is random depending on CPU Load or other things.
Now let's say I put SyncTime at its minimum value > I resync every 1ms
Doing the same thinking would put me Ahead of time by 0.139 microsec < inferior to the precision I want. Therefore if I call the function at 9.999 ms, so 1microsec before reset I will plot 9.999. And just after I will plot 10.000. I will have a good order.
So here the other constraint is : accuracy-ratio x SyncTime < precision level , lets say to be sure because number can be rounded up that accuracy-ratio x SyncTime < precision level/2 is good.
The issue is resolved.
So a Quick recap would be :
Retrieve your timer resolution.
Compute an estimate of the out-of-sync ratio.
accuracy ratio >= out-of-sync ratio estimate , Best accuracy = out-of-sync ratio
Choose your Precision Level considering the following:
timer-resolution <= SyncTime <= PrecisionLevel/(2*accuracy-ratio)
The best Precision you can achieve is timer-resolution*2*out-of-sync ratio
For the above ratio (0.5/hr) the correct SyncTime would be 3.6ms, so rounded down to 3ms.
With the above ratio and the timer resolution of 1ms. If you want a one-tick Precision level (0.1microsec), you need an out-of-sync ratio of no more than : 180ms/hour.
In its last answer to its own answer MusiGenesis state:
#Hermann: I've been running a similar test for the last two hours (without the reset correction), and the Stopwatch-based timer is only running about 400 ms ahead after 2 hours, so the skew itself appears to be variable (but still pretty severe). I'm pretty surprised that the skew is this bad; I guess this is why Stopwatch is in System.Diagnostics. – MusiGenesis
So the Stopwatch accuracy is close to 200ms/hour, almost our 180ms/hour. Is there any link to why our number and this number are so close ? Dont know. But this accuracy is enough for us to achieve Tick-Precision
The Best PrecisionLevel: For the example above it is 0.27 microsec.
However what happen if I call it multiple times between 9.999ms and the re-sync.
2 calls to the function could end-up with the same TimeStamp being returned the time would be 9.999 for both (as I dont see more precision). To circumvent this, you cannot touch the precision level because it is Linked to SyncTime by the above relation. So you should implement Ian Mercer solution's for those case.
Please don't hesitate to comment my answer.
If need the timestamp to perform benchmarks use StopWatch which has much better precision than DateTime.Now.
I think this is the best way to solve this issue:
long timestamp = DateTimeOffset.Now.ToUnixTimeMilliseconds();