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C# Continuously / uninterrupted reading data (from third party SDK)

Intro:
I am developing software that uses motion trackers to analyse human motor systems. Currently I am implementing hardware from xsens and using their SDK to receive data from their wireless sensors.
The SDK offers a COM interface with a "getData" method which you call to receive the currently available xyz axis data (simplified). If you do not call getData, you skip that "beat" so you will be missing data, there is no caching in their hardware/SDK.
Problem:
My problem is that I need to get data at a rate of at least 75Hz, preferably a bit more, but 75 would be acceptable, but I am currently quickly dropping to just 20 signals per second...
If I remove the processing bit (see the sample below) I get perfect sample rates, so I think either the dequeue is causing the enqueue to pause. Or the "heavy" CPU load is causing all threads to wait. I have no idea how to figure out what is actually causing it, the profiler (EQATEC) just shows my "GetData" method is taking longer after a while.
Question:
What is the best technique to use to accomplish this? Why would my "reading" thread be interrupted/blocked? There must be more cases where people need to read from something without being interrupted, but I have been Googleing for 2 weeks now and apparently I can't find the correct words.
Please advise.
Thanks
Simplified code sample, version 4, using a MultiMedia timer (http://www.codeproject.com/Articles/5501/The-Multimedia-Timer-for-the-NET-Framework) and a BackgroundWorker
public class Sample
{
private MultiMediaTimer _backgroundGetData;
private bool _backgroundGettingData;
private BackgroundWorker _backgroundProcessData;
private ConcurrentQueue<double> _acceleration = new ConcurrentQueue<double>();
private void StartProcess()
{
if (_backgroundGetData == null)
{
_backgroundGetData = new MultiMediaTimer {Period = 10, Resolution = 1, Mode = TimerMode.Periodic, SynchronizingObject = this};
_backgroundGetData.Tick += BackgroundGetDataOnTick;
}
_backgroundProcessData = new BackgroundWorker {WorkerReportsProgress = false, WorkerSupportsCancellation = true};
_backgroundProcessData.DoWork += BackgroundProcessDataOnDoWork;
_backgroundGetData.Start();
}
private void BackgroundProcessDataOnDoWork(object sender, DoWorkEventArgs doWorkEventArgs)
{
double value;
if (!_acceleration.TryDequeue(out value)) value = 0;
//Do a lot of work with the values collected so far,
//this will take some time and I suspect it's the cause of the delays?
}
private void BackgroundGetDataOnTick(object sender, EventArgs eventArgs)
{
if (_backgroundGettingData) return;
_backgroundGettingData = true;
//123 represents a value I am reading from the sensors using the SDK
double value = 123;
if (value == -1)
{
Thread.Sleep(5);
continue;
}
_acceleration.Enqueue(value);
if (_acceleration.Count < 5) continue;
if (!_backgroundProcessData.IsBusy)
{
_backgroundProcessData.RunWorkerAsync();
}
_backgroundGettingData = false;
}
}

I am seeing the problem here
_backgroundProcessDataThread.Start();
while (!_backgroundProcessDataThread.IsAlive){}
_backgroundGetDataThread.Start();
while (!_backgroundGetDataThread.IsAlive) {}
Well, you can see here that you are having infinite loop here and the second thread starts only after first has finished its work. i.e. first thread is done. This is in no way an ideal model.
Sorry, I recognized the issue later.
The problem is, _backgroundGetDataThread will start only after _backgroundProcessDataThread has done its work.

Using Timer and colour to display morse code

Hi Guys i'm trying to let my Screen blink a morse code out using timer , but no luck, can you spot any problem?
Sry but i feel sad for those who cant think out of the box and just mark a -2 without even understanding the situation.
Anyway, found about using await Task.Delay(100) but gridHalfFront.Opacity = 1; isnt being "activated" when its being read. not sure why.
async public void RunMorseCode()
{
foreach (char c in word.ToCharArray())
{
string rslt = Codes[c.ToString()].Trim();
foreach (char c2 in rslt.ToCharArray())
{
if (c2 == '.')
{
gridHalfFront.Opacity = 0;
await Task.Delay(100);
}
else
{
gridHalfFront.Opacity = 0;
await Task.Delay(1000);
}
gridHalfFront.Opacity = 1;
}
}
}

use System.Threading.Thread.Sleep(1000) and/or System.Threading.Thread.Sleep(3000) inside yr loop to make yr screen blink on and off
gridHalfFront.Opacity = 1;
if (c2 == '.')
{
System.Threading.Thread.Sleep(1000);
}
else
{
System.Threading.Thread.Sleep(3000);
}
gridHalfFront.Opacity = 0;
change it to the way it best for you, but dont use those timers

Your code is missing the Timer event handler. After calling Start() and after the elapsed time a Tick event from the Timer will be raised. There you have to change the opacity.

I think you are misunderstanding the use of a Timer. If you put the following code at the top of StartTimer you will see what I mean.
Console.WriteLine("Started {0}", inputTiming);
When you run you will get a bunch of timers are being created immediately. This is not what you want for two reasons. Firstly, they are all assigned to the same variable, so the second is 'logically' killing off the first, etc. Secondly, you don't want them created all at once, as all of the 1 second ones will all run at the same time after 1 second, and all of the 3 second ones will run together after 3 seconds. And, as already mentioned, to run code after the timer expires you need to hook up the event.
BIG EDITS Sorry didn't realise you were looking at Metro. What I have said above still holds, but I will back away from providing a solution.
Given the comments about Sleep() not working on Metro, I think you need to so all the code inside the timer for one character, and then set the interval for the next character from within the timer. Will provide some code in a few minutes...

Have MessageBox appear once (code inside timer)

UPDATE: I've managed to fix my problem. Using the code below, I moved my MessageBox AFTER my XML saving and changed the Timer from 100ms to 400ms. I now have 1 box appear, thank god. Although If anyone has a short cut to updating a single value (ActReminded) in the List array(ActListTask), that'd be great to know.
I'm having a little issue with displaying the MessageBox. Show inside a timer without it spamming me. Here's the part of the code I've been working with:
public class ActiveTasks
{
//Properties here
}
public List<ActiveTasks> ActTaskList = new List<ActiveTasks>();
for (int i = 0; i < ListActive.Items.Count; i++)
{
if (DTime.Date == newDateTime.Date)
{
if (newDateTimeLeft.CompareTo(TimeSpan.Zero) <= 0 && ActTaskList[i].ActReminded != "true")
{
MessageBox.Show("!!!!");
ActTaskList.Add(new ActiveTasks()
{
ActTitle = ActTaskList[i].ActTitle,
ActDesc = ActTaskList[i].ActDesc,
ActDate = ActTaskList[i].ActDate,
ActTime = ActTaskList[i].ActTime,
ActStatus = ActTaskList[i].ActStatus,
ActReminded = "true",
ActRepeat = ActTaskList[i].ActRepeat
});
ListActive.Items.RemoveAt(i);
ActTaskList.RemoveAt(i);
XDocument XmlActTasks = GenerateActiveListToXML(ActTaskList);
}
}
}
I actually decided I may want to hold onto the reminder status, whether it has been shown or not as I wouldn't want a repeated reminder every time the program is opened. Since I don't know of a way to update an individual part of ActTaskList I just re-added it, and then deleted the original. This code manages to recognise that if it happens, it will change the reminder status from false, to true; after I've Ok'ed all the spam. So it will stop the MessageBox once I've managed to closed all the Messageboxes. However, it doesn't stop the spam. Would it be anything to do with the fact I've set the timer to 100ms? Or could their be an alternative way to make the messagebox appear without it being inside the timer?

The odds of the current time lining up exactly to the second what is happening in your loop is small. Why not treat newDateTime as a cut off point and just set a flag?
//Declare this outside of the loop
bool hasDisplayed = false;
//Inside the timer event handler
if (!hasDisplayed && DateTime.Now >= newDateTime)
{
hasDisplayed = true;
MessageBox.Show("!!!!!!!!!!!!!");
}

Can you do something like this?
Action message = () => MessageBox.Show("!!!!!!!!!!!!!"));
object lockOb = new object();
void timer_Elapsed(object sender, ElapsedEventArgs e)
{
lock(lockOb)
if(null != message)
{
message();
message = null;
}
}

You say you've already tried a boolean indicating the message has already been shown, I'm assuming because the code probably looked like it did below.
void TimerLoop()
{
bool msgAlreadyShown;
if(!msgAlreadyShown)
{
MessageBox.Show("!!!!!!!");
}
// Other work in your timer function
}
The problem with that code is that the bool will be set to false each time the function is called by the timer. You haven't posted much code, but you've at least stated what you're trying to accomplish, a timer that checks if a reminder should be presented to the user.
I'm about to make some wild guesses about how you've put together your software, there's a good chance it's way off, but I hope it might point you in the right direction. You could have some sort of reminder class like this:
public class Reminder
{
string Message { get; set;}
DateTime Alarm { get; set; }
bool IsDismissed { get; set; }
}
I'm assuming you might want to have multiple reminders that can be checked for in the timer loop, so your timer loop could look something like:
private List<Reminder> _activeReminders; // A list of reminders
void TimerLoop(object s, ElapsedEventArgs e)
{
lock(_activeReminders)
{
var now = DateTime.Now;
foreach(var reminder in _activeReminders)
{
// only run this code if the time has passed and it hasn't already
// been shown
if(now.CompareTo(reminder.Alarm) >= 0 && !reminder.IsDismissed)
{
MessageBox.Show(reminder.Message);
reminder.IsDismissed = true;
}
}
}
}
This is a pretty naive implementation, since you probably don't want to hold onto the reminders for forever and the reminders are never removed from the _activeReminders list, but you essentially just need to add some sort of state to determine if the reminder has already been shown.
Of course, this isn't a complete example either, since I never new up the _activeReminders field or add anything to it, but I think this might help get the idea of what you need to do across. Also, you might not care about multiple reminders, and your timer code could look nothing like this. The main idea was to show you how you can keep track of the state of a reminder, and tailor it to your own code. The above was just an example.
Also, I haven't actually tested it, so treat it more like pseudocode than anything else. However, the logic is sound, and should it should only cause the message box to appear once.

how to execute certain class method no more than once per 100ms?

I'm writing trading software and need to QoS one method that should not be executed more often than 10 times per second. As I'm begginer in C# and almost not familar with libraries I would like to double-check if my code is "optimal". I'm using Stopwatch because I don't know any other timers in C#.
Stopwatch updateStopwatch = Stopwatch.StartNew();
private void update()
{
if (updateStopwatch.ElapsedMilliseconds < 100)
{
Console.WriteLine("!skip update " + updateStopwatch.ElapsedMilliseconds);
return;
} else
{
Console.WriteLine("!update");
updateStopwatch.Restart();;
}
// do work here
}
upd Now it seems that Stopwatch is pretty good for this task. However probably it would be too slow, if so probably DateTime would be better. sell also Stopwatch vs. using System.DateTime.Now for timing events

Your technique of using Stopwatch is the best solution to prevent the code from executing more frequently. As others have said, using a Timer is a better solution if you want to make sure that the method is executed on a schedule.
Any approach based on DateTime is fundamentally broken because it will fail when the date changes. This is especially noticeable during the Daylight Saving Time switches. When we "spring ahead", there's the potential of the update running twice in quick succession because the code thinks that it's been an hour since the previous update. That's not too bad. But when we "fall back", the update will be suspended for a full hour because the last update time is set an hour ahead.
The same kind of thing can happen, although not as severely, if your computer is set to update its time periodically from an NTP server. If the time is set ahead, then there is the potential for two updates to happen in quick succession. If the time is set back, there's the potential for updates not to happen for the amount of time the clock was set back.
There are ways around the problem (such as using the absolute value of the number of milliseconds), but then you're just putting a bandage on a broken solution. You shouldn't depend on DateTime for intervals like this because your program isn't in control of the system clock--it can change at any time.
Stopwatch is the only reasonable solution here because it depends on the CPU's performance counter, which only increases. You don't have the problems of somebody setting the counter back, and you don't have the rollover problems you would encounter with something like Environment.TickCount.
There's some idea that Stopwatch incurs a performance penalty that DateTime doesn't. My testing shows that to be untrue.

Stopwatches and timers are fairly expensive objects to use. You could simply hold a DateTime object as a variable and perform a comparison.
DateTime lastCheck = DateTime.Now;
private void update()
{
// DateTime.Subtract returns a TimeSpan
int elapsed = DateTime.Now.Subtract(lastCheck).Milliseconds;
if (elapsed < 100)
{
Console.WriteLine("!skip update " + elapsed.ToString());
return;
} else
{
Console.WriteLine("!update");
lastCheck = DateTime.Now;
}
// do work here
}

I would not use a Stopwatch or anything other Timer-like. Instead just store the time of the method call and only execute the subsequent calls if the difference between the current and the stored time is bigger than 100ms.
You could implement a helper class to do this in a more general way:
public class TimedGate
{
private DateTime m_Last;
private TimeSpan m_Gap;
public TimedGate(TimeSpan gap)
{
m_Gap = gap;
}
public bool TryEnter()
{
DateTime now = DateTime.UtcNow;
if (now.Subtract(m_Last) > m_Gap)
{
m_LastEntered = now;
return true;
}
return false;
}
}
Use it like this:
TimedGate m_UpdateGate = new TimedGate(TimeSpan.FromMilliseconds(100));
private void Update()
{
if (m_UpdateGate.TryEnter())
{
Console.WriteLine("!update");
// do work here
}
else
{
Console.WriteLine("!skip update");
}
}

There is always the System.Timer timer.
That is probably easier to work with than the Stopwatch (which normally is used to measure how long time things take).
Code:
var timer = new System.Timers.Timer();
// Hook up the Elapsed event for the timer using a lambda
timer.Elapsed += (o, e) => Console.WriteLine("Timer elapsed");
// Set the Interval to 100 ms
timer.Interval = 100;
// Start the timer.
timer.Enabled = true;
MSDN docs: http://msdn.microsoft.com/en-us/library/system.timers.timer(v=VS.100).aspx

"Atomically" changing a System.Threading.Timer

Let's say I have an existing System.Threading.Timer instance and I'd like to call Change on it to push it's firing time back:
var timer = new Timer(DelayCallback, null, 10000, Timeout.Infinite);
// ... (sometime later but before DelayCallback has executed)
timer.Change(20000, Timeout.Infinite);
I'm using this timer to perform an "idle callback" after a period of no activity. ("Idle" and "no activity" are application-defined conditions in this case...the specifics aren't terribly important.) Every time I perform an "action", I want to reset the timer so that it is always set to fire 10 seconds after that.
However, there is an inherent race condition because when I call Change, I can't tell if the Timer has already fired based on its old settings. (I can, of course, tell if my callback has happened but I can't tell if the CLR's internal timer thread has queued my callback to the threadpool and its execution is imminent.)
Now I know I can call Dispose on the timer instance and re-create it each time I need to "push it back". but this seems less efficient than just changing the existing timer. Of course it may not be...I'll run some micro-benchmarks in a bit and let you all know.
Alternatively, I can always keep track of the expected firing time (via DateTime.Now.AddSeconds(10)) and, if the original Timer fires, ignore it by checking DateTime.Now in the callback. (I have a nagging concern that this may not be 100% reliable on account of the Timer using TimeSpan and my check using DateTime...this may not be an issue but I'm not completely comfortable with it for some reason...)
My questions are:
Is there a good way for me to call Timer.Change and be able to know whether I managed to change it before the callback was queued to the threadpool? (I don't think so, but it doesn't hurt to ask...)
Has anyone else implemented (what I term) a "pushback timer" like this? If so, I'd love to hear how you tackled the problem.
This question is somewhat hypothetical in nature since I already have a couple of working solutions (based on Dispose and based on DateTime.Now)...I'm mainly interested in hearing performance-related suggestions (as I'll be "pushing back" the Timer VERY frequently).
Thanks!

it sounds like what you really want is the application-idle event
System.Windows.Forms.Application.Idle

Im interpreting your questions as a request for an implementatation of the IdleNotifier interface specified below. Also you state that ActionOccured() needs to be fast.
public delegate void IdleCallback();
public interface IdleNotifier
{
// Called by threadpool when more than IdleTimeSpanBeforeCallback
// has passed since last call on ActionOccured.
IdleCallback Callback { set; }
TimeSpan IdleTimeSpanBeforeCallback { set; }
void ActionOccured();
}
I provide an implementation with System.Threading.Timer below.
Important points about the implementation:
We accept that the timer can wake up at any time and make sure this is ok.
Since we assume the timer wakes relatively seldom we can do expensive work at these times.
Since we can do all logic in the timer callback all we need to do to "push the timer" is to remeber when last we pushed it.
Implementation:
public class IdleNotifierTimerImplementation : IdleNotifier
{
private readonly object SyncRoot = new object();
private readonly Timer m_Timer;
private IdleCallback m_IdleCallback = null;
private TimeSpan m_IdleTimeSpanBeforeEvent = TimeSpan.Zero;
// Null means there has been no action since last idle notification.
private DateTime? m_LastActionTime = null;
public IdleNotifierTimerImplementation()
{
m_Timer = new Timer(OnTimer);
}
private void OnTimer(object unusedState)
{
lock (SyncRoot)
{
if (m_LastActionTime == null)
{
m_Timer.Change(m_IdleTimeSpanBeforeEvent, TimeSpan.Zero);
return;
}
TimeSpan timeSinceLastUpdate = DateTime.UtcNow - m_LastActionTime.Value;
if (timeSinceLastUpdate > TimeSpan.Zero)
{
// We are no idle yet.
m_Timer.Change(timeSinceLastUpdate, TimeSpan.Zero);
return;
}
m_LastActionTime = null;
m_Timer.Change(m_IdleTimeSpanBeforeEvent, TimeSpan.Zero);
}
if (m_IdleCallback != null)
{
m_IdleCallback();
}
}
// IdleNotifier implementation below
public void ActionOccured()
{
lock (SyncRoot)
{
m_LastActionTime = DateTime.UtcNow;
}
}
public IdleCallback Callback
{
set
{
lock (SyncRoot)
{
m_IdleCallback = value;
}
}
}
public TimeSpan IdleTimeSpanBeforeCallback
{
set
{
lock (SyncRoot)
{
m_IdleTimeSpanBeforeEvent = value;
// Run OnTimer immediately
m_Timer.Change(TimeSpan.Zero, TimeSpan.Zero);
}
}
}
}
There are many straight-forward performance improvements on this code.
If anyone would be intrested in my first thoughts on this just ask me.

I've actually had to build my own "Timing" class for an MMORPG I've made. It could keep track of over 100,000 "entities" that had timers for processing AI, and other tasks. Based on different actions that could be taken, I would have to momentarily delay an event.
Now, my timing class was completely hand written, so it won't be exactly what you're looking for. But something that you could do that would be similar to the solution I came up with is to do a sort of:
while (sleepyTime > 0)
{
int temp = sleepyTime;
sleepyTime = 0;
Thread.Sleep(temp);
}
// here's where your actual code is.
Then, you can make a "Delay" method that basically just ads to sleepyTime.