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C#: How to implement keep alive timers for many objects in a proper and efficient way? [closed]

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What I want to realize is easily explained, but because there are so many different possibilities I'm not really aware of the pro and cons for each possible approach:
In my application there are plenty (say some thousands of communication objects).
When such object is idle for some while (meaning that certain methods are not called), it shall simply be closed (what this means in detail is not relevant here).
I'm thinking of a "timer", associated with each object, which is re-triggered every time I "use" the object. Like:
public void ReTrigger()
{
lock (_some_locking)
{
//Reset the timer
_timer.Stop();
_timer.Start();
}
}
}
Note, my application is heavily using async/await and I would like to use a solution which fits best into this concept. I want to avoid a lot of additional threads just for running a lot of timers.
There are many different timers available:
System.Timers.Timer
System.Threading.Timer
System.Windows.Forms.Timer
System.Web.UI.Timer
System.Windows.Threading.DispatcherTimer
So, which one "fits" best into my concept of using asyncio ?
To put an alternative, would it be better to rely on a background task like
while (true)
{
try
{
await Task.Delay(timeout, _cancellationToken)
... some action when expired ...
}
catch (TaskCanceledException)
{
// we have been re-triggered by "using" the object
}
}
This fits better in my concept, however, in this case I need a new cancellation token after each re-trigger, which is not really nice.
What is the "golden way" way to solve my problem; preferably using async tasks?
Another solution would be a housekeeping task, which cyclically polls all active objects for being expired or not. This would work with just one running timer, but is also not very nice.

Here is a way to keep track of the expiration status of an object passively, without using timers. The last time that each object was used is stored in a private double field, and this field is updated every time the object is used. In case the object has not been used for a long time, the field will take the value double.MaxValue which means "expired", and will keep this value forever. The GetExpired method below handles the complexity of comparing and updating the field atomically and with thread-safety:
public static bool GetExpired(ref double lastUsed, TimeSpan slidingExpiration,
bool touch)
{
// Magic values, 0: Not initialized, double.MaxValue: Expired
double previous = Volatile.Read(ref lastUsed);
if (previous == double.MaxValue) return true;
// Get current timestamp in seconds
double now = (double)Stopwatch.GetTimestamp() / Stopwatch.Frequency;
if (previous == 0D || now - previous < slidingExpiration.TotalSeconds)
{
// Not expired (unless preempted)
if (!touch) return false;
var original = Interlocked.CompareExchange(ref lastUsed, now, previous);
return original == double.MaxValue;
// In any other case that original != previous we've lost the race to update
// the field, but its value should be very close to 'now'. So not expired.
}
else
{
// Expired (unless preempted)
var original = Interlocked.CompareExchange(ref lastUsed, double.MaxValue,
previous);
return original == double.MaxValue || original == previous;
}
}
Usage example:
public class MyComObject
{
private readonly TimeSpan _slidingExpiration = TimeSpan.FromSeconds(60);
private double _lastUsed;
public MyComObject() // Constructor
{
GetExpired(ref _lastUsed, default, touch: true); // Start expiration "timer"
}
public bool IsExpired => GetExpired(ref _lastUsed, _slidingExpiration, touch: false);
public bool TryDoSomething()
{
if (GetExpired(ref _lastUsed, _slidingExpiration, touch: true)) return false;
//...
return true; // The job was done
}
}

Autoclicker calculation

I'm making autoclicker program and I already have an issue. I want my program to be able to change the clicks per second field just how the user wants it. So I made this.
private void textBoxCps_TextChanged(object sender, EventArgs e)
{
try
{
time = Convert.ToDouble(textBoxCps.Text);
time = 1000 / time;
Math.Round(time);
}
catch (Exception)
{
}
}
The math is right(I think...)
while (IsRunning)
{
if ((Control.ModifierKeys & Keys.Alt) != 0)
{
DoMouseClicks();
Thread.Sleep(Convert.ToInt32(time));
}
else
{
}
}
When I try to put 1 CPS into the textbox it does 1 click per second, the same for 2 and 3 but when it's 4 and higher I'm getting 3.80 and lower CPS.

So the operator types some text that should represent a period of time (TimeSpan), and after running is started, you want to call method DoMouseClicks every TimeSpan, until running is stopped.
One of the problems is, that while you are doing this procedure you want your user input to be responsive.
Instead of Sleep, you should use one of the windows timers. There are several of them, and each have their advantages and disadvantages. In your case, the timer that you use depends on the accuracy that you need. See this article for a comparison between the various timers
Is it a problem if the clicks are a bit delayed if the user thread is busy? If not, the easiest is a System.Timers.Timer
System.Timers.Timer timer = new System.Timers.Timer()
timer.Elapsed += TimerElapsed;
private void TimerElapsed(object sender, ...)
{
DoMouseClicks();
}
To change the interval:
TimeSpan TimerInterval
{
get => TimeSpan.FromMilliseconds(this.timer.Interval);
set => this.Timer.Interval = value.TotalMilliseconds;
}
I decided to use a TimeSpan as interval time. This way you code changes are minimal if in future versions you decide to let the operator type his interval times in seconds, or in time format ("01:00")
To start and stop the timer:
private bool IsTimerStarted
{
get => this.timer.Enable;
set => this.timer.Enabled = value;
}
Now we are ready to react on operator input. You decided to act on TextBoxChanged. Are you sure you want this? What happens if an operator wants to type "1000", to indicate one second time interval. He starts by typing "1", you immediately start the mouse clicks with a frequency of 1 msec. Is this what you want?
Another problem: if the operator makes a typing error: "10)0", instead of "1000"?
A proper user interface would let the operator indicate that he finished typing the interval by pressing a button. When the button is pressed you read the text. If there is an error, you notify the operator, if not, you start the timer.
An alternative is to disable the button as long as the text box contains invalid text. Although this seems nice, the disadvantage is that the operator does not know why his button is not enabled.
private void OnButtonStart_Clicked(object sender, ...)
{
TimeSpan intervalTime = this.ReadTextBoxInterval();
this.TimerInterval = intervalTime;
this.IsTimerStarted = true;
// if desired: show the operator that the action is running
}
private void OnButtonStop_Clicked(object sender, ...)
{
this.IsTimerStarted = false;
// if the timer was handling event Elapsed, it is finished neatly.
// if desired show the operator that the action is stopped.
}
I decided to separate the action from the interpretation of the operator input. This way, code changes are minimal if you decide to change the operator input from msec to seconds, or even time format ("00:01"). Or if you decide to use a ComboBox instead of an edit box.
TimeSpan ReadTextBoxInterval()
{
string textBoxText = this.TextBoxInterval.Text;
return IntervalFromMsecText(textBoxText);
}
TimeSpan IntervalFromMsecText(string intervalText)
{
if (Double.TryParse(intervalText, NumberStyles.Any, CultureInfo.CurrentCulture,
out double msecInterval))
{
// input is a proper double
return TimeSpan.FromMilliseconds(msecInterval);
}
else
{
// invalid input. Notify the operator?
}
}

How to handle the TextChanged event only when the user stops typing?

I have a TextBox with a TextChanged event wired up. In the end it is making a query to a SQL database, so I want to limit the number of queries.
I only want to make the query if the user hasn't pressed a key in say .. 300 milliseconds or so. If for some reason the previous query is still executing, I would need to cancel that, and then issue a new query.

Create a System.Windows.Forms.Timer and reset it (e.g. stop then start it) after every keypress. If the timer event is triggered, disable the timer.

Use the Reactive Framework to trigger on a sequence of events. I'm not sure exactly how this would work, but you can read up on it here (Reactive Extensions for .NET) and see if it will fulfill your needs. There are a bunch of examples here too: Examples. The "Throttling" example may be what you're looking for.

1) Create a timer.
2) Create a handler for the Tick event of your timer. On each tick, check to see if enough idle time has elapsed, and if it has, STOP the timer and execute the query.
3) Whenever a keypress occurs on that textbox, RESTART the timer.

Add a second actionlistener that gets called whenever the user presses any key and when it gets called save the current time to a global variable. Then whenver your TextChanged event gets called it checks to see the time difference between the global variable and the current time.
If the difference is less than 300 milliseconds then start a timer to execute the query after 300 milliseconds. Then if the user presses another key it resets the timer first.

Thanks to #Brian's idea and this answer , I came up with my own version of using a timer to handle this issue. This worked fine for me. I hope it helps the others as well:
private Timer _tmrDelaySearch;
private const int DelayedTextChangedTimeout = 500;
private void txtSearch_TextChanged(object sender, EventArgs e)
{
if (_tmrDelaySearch != null)
_tmrDelaySearch.Stop();
if (_tmrDelaySearch == null)
{
_tmrDelaySearch = new Timer();
_tmrDelaySearch.Tick += _tmrDelaySearch_Tick;
_tmrDelaySearch.Interval = DelayedTextChangedTimeout;
}
_tmrDelaySearch.Start();
}
void _tmrDelaySearch_Tick(object sender, EventArgs e)
{
if (stcList.SelectedTab == stiTabSearch) return;
string word = string.IsNullOrEmpty(txtSearch.Text.Trim()) ? null : txtSearch.Text.Trim();
if (stcList.SelectedTab == stiTabNote)
FillDataGridNote(word);
else
{
DataGridView dgvGridView = stcList.SelectedTab == stiTabWord ? dgvWord : dgvEvent;
int idType = stcList.SelectedTab == stiTabWord ? 1 : 2;
FillDataGrid(idType, word, dgvGridView);
}
if (_tmrDelaySearch != null)
_tmrDelaySearch.Stop();
}

Problem While receiving events from a thread

I'm Doing a project on FileTransfer in which i have a listview , i will get events from one of my class file for updating the percentage of the file sent so far,after receiving it i will place the percentage in my listview ,while doing that the listview got
a flickering effect how to avoid it.i used application.doevents() but it doesnt works. i have seen in torrents while updating the percent the list doesnt get flickered
how to achieve this .
void Sender_Progress(int CurrentValue, string Ip) // here im receiving Events
{
try
{
//if (CurrentValue == 1)
// UpdateTimer.Enabled = true;
//list_send.Items[CurrentValue].SubItems[4].Text = Ip.ToString();
//Application.DoEvents();
obj = new object[] {CurrentValue, Ip };
list_send.Invoke(new UpdateList(UpList), obj);
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}
}
public void UpList(int Val, string ind) // here im updating the listview
{
Application.DoEvents();
int index = 0;
index = Convert.ToInt32(ind);
index = index - 1;
list_send.Items[index].SubItems[4].Text = Val.ToString();
if (Val == 100)
{
list_send.Items[index].SubItems[2].Text = "Completed.";
//UpdateTimer.Enabled = false;
}
//Application.DoEvents();
}

Firstly, you don't need the DoEvents, since you are already correctly working on two threads. Remove that. After that, I expect the problem is simply doing too much too quickly. Is it possible to batch updates, and only send an update, say, every 20? 50? times? It isn't clear what the control is, but many have multiple-update modes; for example with ListView:
theList.BeginUpdate();
try {
// make multiple updates here...
} finally {
theList.EndUpdate();
}
I would then see about passing over a list of updates, say, every 20 times (unless each takes a considerable time) [note it must be a different list per Invoke, and you need to remember to send any remaining items at the end, too].

Use worker thread - it's available from the toolbox and has two events that are invoked in the main (UI) thread.
The Progress event can be used to signal the listbox that it need to refresh or that the task was completed.

i overcome the flickering effect succesfully,im getting events frequently ,i will get an integer everytime, i will store it in a variable and compare it with next variable received by the event if it matches i wont invoke the listview,otherwise i will invoke it.now the flickering goes away. thanks all.

C# WinForms: Waiting for a button press inside an infinite loop

I'm making a simple Guess-The-Number game with a GUI. I need to wait on a loop waiting for the user to input a number in a text box and press "OK". How do I wait for an event inside a loop?
Note: I don't want message boxes. This is done in the main window, hence the need to wait for input.
EDIT: I should have explained myself better. I know that there's a loop inside the GUI. What I want is another loop inside a method. Maybe there's a better way to do this. I could code stuff inside the button's event handler, now that I think about it. Although I'd need global variables. Whataver, I'll think about it, but I hope my question is clearer now.
EDIT 2: Sorry that my question wasn't clear and the edit didn't do much help. First of all, the code is too big to be posted here. I'd probably have to post a screenshot of the GUI, so it wouldn't be of much use. Basically, I have two fields, "Max number" and "Number of allowed guesses". The user enters these two and clicks "Play". A new panel becomes available, with a text box and a "Guess" button. The user enters a guess, and the program checks to see if it's correct.
The purpose of the second infinite loop is to avoid global variables. See, each time the user clicks "Play", the game has to generate a new random number as the correct guess. If everything is done inside a method, no problem. But if the "Guess" button's event handler is called multiple times, the number has to be stored as an instance variable of the Form. Sure, it's not big deal, but I think the number should be a property of the method directing the current game, not of the Form.
I'd also have to keep track of the remaining number of guesses outside of the method. Again, it's no big deal. I just want to avoid globals if I can.
Again, I'm sorry that my question wasn't too clear. I'm kind of tired, and I didn't feel like writing too much. If this still isn't clear, then don't bother. I'll think of something.

C# automatically loops infinitely waiting for events until your form is closed. You just need to respond to the button click event.

Jason Down's suggestion is wise, create a new GuessingGame class and add it to your project. I know you're worried about "global variables" (which everyone is taught in school never to use unless you absolutely have to), but think about your design specifications for a minute.
But if the "Guess" button's event handler is called multiple times, the number has to be stored as an instance variable of the Form. Sure, it's not big deal, but I think the number should be a property of the method directing the current game, not of the Form.
As an alternative, store an instance of your GuessingGame class in the form. This is not a global variable! You said so yourself, the point of the game is keep track of the guesses and generate new numbers to guess every time "Play" is clicked. If you store an instance of the game in the form then open another form (e.g. a Help or About box), then the game's instance would not be available (thus, not global).
The GuessingGame object is going to look something like:
public class GuessingGame
{
private static Random _RNG = new Random();
private bool _GameRunning;
private bool _GameWon;
private int _Number;
private int _GuessesRemaining;
public int GuessesRemaining
{
get { return _GuessesRemaining; }
}
public bool GameEnded
{
get { return !_GameRunning; }
}
public bool GameWon
{
get { return _GameWon; }
}
public GuessingGame()
{
_GameRunning = false;
_GameWon = false;
}
public void StartNewGame(int numberOfGuesses, int max)
{
if (max <= 0)
throw new ArgumentOutOfRangeException("max", "Must be > 0");
if (max == int.MaxValue)
_Number = _RNG.Next();
else
_Number = _RNG.Next(0, max + 1);
_GuessesRemaining = numberOfGuesses;
_GameRunning = true;
}
public bool MakeGuess(int guess)
{
if (_GameRunning)
{
_GuessesRemaining--;
if (_GuessesRemaining <= 0)
{
_GameRunning = false;
_GameWon = false;
return false;
}
if (guess == _Number)
{
_GameWon = true;
return true;
}
else
{
return false;
}
}
else
{
throw new Exception("The game is not running. Call StartNewGame() before making a guess.");
}
}
}
This way, all the data related to the game is encapsulated within the class. Hooking up the events is easy in the codebehind of the form:
GuessingGame game = new GuessingGame();
private void btnPlay_Click(object sender, EventArgs e)
{
int numberOfGuesses = Convert.ToInt32(txtNumberOfGuesses.Text);
int max = Convert.ToInt32(txtMax.Text);
game.StartNewGame(numberOfGuesses, max);
}
private void btnGuess_Click(object sender, EventArgs e)
{
int guess = Convert.ToInt32(txtGuess.Text);
bool correct = game.MakeGuess(guess);
if (correct)
lblWin.Visible = true;
if (game.GameEnded)
{
// disable guess button, show loss label
}
}

You should probably look for a book to actually learn windows programming.
The very basics:
1) There is already an infinite loop deep down in the windows code somewhere. Any windows program is constantly looping and scanning for input.
2) Once input is found, this loop fires off an Event.
3) Your mission, should you choose to accept it, is to write event handlers to handle those events.

you are most likely doing it wrong as it has already been pointed out, but you can use this
Application.DoEvents();
to process events when you are on an actual loop
to do it the right way
- don't use a loop
- use an edit box for the input, then a button
- implement the button onclick event

Yes, and What if I am waiting for Speech events, it could happen anytime event when a function is running, I need to handle that without recursively call a function