I would like to add more delay in delay var while the execution waits
Example:
private System.Threading.Tasks.Task delayVar; //Delay var
private async void createDelay() //First function
{
delayVar = System.Threading.Tasks.Task.Delay(milliseconds);
await delayVar;
}
private void addDelay() //Second function
{
delayVar.Milliseconds +=5000;
}
Thanks.
You can't "reset" a Task.Delay, but you can reset a timer which makes it an ideal candidate to solve this problem.
Here's an example:
private System.Threading.Timer timer;
public void Start()
{
timer = new System.Threading.Timer(_ => fireMyCode());
restartTimer();
}
private void onFileChanged(object sender, EventArgs e)
{
restartTimer();
}
private void restartTimer()
{
timer.Change(TimeSpan.FromMinutes(5), TimeSpan.FromMinutes(5));
}
But you don't have to use timers, you can still use Task.Delay with an additional task: the idea is to wait on two tasks, the delay and waiting for the files to change (you can use TaskCompletionSource to "create" a task from an event). If the delay task completes first, fire your code.
Here's an example:
TaskCompletionSource<object> fileChanged = new TaskCompletionSource<object>();
private void onFileChanged(object sender, EventArgs e)
{
fileChanged.TrySetResult(null);
}
private async Task endlessLoop()
{
while (true)
{
await handleFilesNotChanged();
}
}
private async Task handleFilesNotChanged()
{
Task timeout = Task.Delay(TimeSpan.FromMinutes(5));
Task waitForFile = fileChanged.Task;
if (await Task.WhenAny(timeout, waitForFile) == timeout)
{
fireMyCode();
}
fileChanged = new TaskCompletionSource<object>();
}
Related
We have below class members for timer:
private Timer _activityTimer;
Instantiating this timer variable in one method:
_activityTimer =
new Timer(async (timerState) => await UpdateActivityAsync(_ipAddress), null, new Random().Next(1, 15000), 15000);
But this did not calling periodically when server has load.
It is showing below log in serilog:
Starting HttpMessageHandler cleanup cycle with {InitialCount} items
Ending HttpMessageHandler cleanup cycle after {ElapsedMilliseconds}ms - processed: {DisposedCount} items - remaining: {RemainingItems} items
To handle async periodic callback, I would use System.Threading.PeriodicTimer. This way the execution of the next UpdateActivityAsync will not begin until the last one is done. If you still face thread pool starvation issue, you could manually create an additional thread in which you run the timer.
class Example {
private PeriodicTimer _activityTimer;
private IPAddress _ipAddress = IPAddress.Parse("192.168.1.1");
public void StartTimer() {
// Starting the timer, but not awaiting to not block the calling thread
// If you still face thread pool starvation issue, you could manually create an additional thread here
StartTimerLoopAsync();
}
public void StopTimer() {
_activityTimer.Dispose();
}
private async Task StartTimerLoopAsync() {
_activityTimer = new PeriodicTimer(TimeSpan.FromMilliseconds(15000));
while (await _activityTimer.WaitForNextTickAsync()) {
await UpdateActivityAsync(_ipAddress);
}
}
private async Task UpdateActivityAsync(IPAddress ipAddress) {
await Task.Delay(500); // Simulate some IO
Console.WriteLine(ipAddress);
}
}
UPDATE for .NET Core 3.1
Instead of PeriodicTimer you could simply use Task.Delay (it's not very accurate, but good enough for your use case I believe):
class Example {
private CancellationTokenSource _cancellationTokenSource = new ();
private IPAddress _ipAddress = IPAddress.Parse("192.168.1.1");
public void StartTimer() {
// Starting the timer, but not awaiting to not block the calling thread
// If you still face thread pool starvation issue, you could manually create an additional thread here
StartTimerLoopAsync();
}
public void StopTimer() {
_cancellationTokenSource.Cancel();
}
private async Task StartTimerLoopAsync() {
await Task.Delay(new Random().Next(1, 15000)); // System.Threading.Timer first delay
while (!_cancellationTokenSource.IsCancellationRequested) {
// run the Delay and UpdateActivityAsync simultaneously and wait for both
var delayTask = Task.Delay(15000, _cancellationTokenSource.Token);
await UpdateActivityAsync(_ipAddress, _cancellationTokenSource.Token);
await delayTask;
}
}
private async Task UpdateActivityAsync(IPAddress ipAddress, CancellationToken cancellationToken) {
await Task.Delay(1500, cancellationToken); // Simulate some IO
Console.WriteLine(ipAddress);
}
}
UPDATE
You could also create your own async Timer:
class Example : IDisposable {
private AsyncTimer<Example>? _timer;
public IPAddress IpAddress = IPAddress.Parse("192.168.1.1");
public void StartTimer() {
if (_timer is not null) {
return;
}
_timer = new AsyncTimer<Example>(async (state, ct) => await UpdateActivityAsync(state.IpAddress, ct), this, new Random().Next(1, 15000), 15000);
}
public void StopTimer() {
_timer?.Stop();
}
private async Task UpdateActivityAsync(IPAddress ipAddress, CancellationToken cancellationToken) {
await Task.Delay(500, cancellationToken); // Simulate some IO
Console.WriteLine(ipAddress);
}
public void Dispose() {
_timer?.Dispose();
}
}
class AsyncTimer<T> : IDisposable {
public delegate Task AsyncTimerDelegate(T state, CancellationToken cancellationToken);
private readonly CancellationTokenSource _cancellationTokenSource = new();
private readonly AsyncTimerDelegate _timerCallback;
private readonly TimeSpan _dueTime;
private readonly TimeSpan _interval;
private readonly T _state;
public AsyncTimer(AsyncTimerDelegate timerCallback, T state, int dueTime, int interval) {
_timerCallback = timerCallback;
_state = state;
_dueTime = TimeSpan.FromMilliseconds(dueTime);
_interval = TimeSpan.FromMilliseconds(interval);
// Starting the timer, but not awaiting to not block the calling thread
// If you still face thread pool starvation issue, you could manually create an additional thread here
StartTimerLoopAsync();
}
public void Stop() {
_cancellationTokenSource.Cancel();
}
private async Task StartTimerLoopAsync() {
await Task.Delay(_dueTime);
while (!_cancellationTokenSource.IsCancellationRequested) {
// run the Delay and UpdateActivityAsync simultaneously and wait for both
var delayTask = Task.Delay(_interval, _cancellationTokenSource.Token);
await _timerCallback.Invoke(_state, _cancellationTokenSource.Token);
await delayTask;
}
}
public void Dispose() {
_cancellationTokenSource.Dispose();
}
}
I am creating a WPF app where I want to have a global bool im assuming, on the first button click I’ll set this bool to true and I want it to run a task (continuously call an API method) until I click the button again and it stops it. What would be the best way to do this?
private bool running = false;
private async void BtnTrade1_Buy_Click(object sender, RoutedEventArgs e)
{
if (!running)
{
running = true;
}
else
running = false;
if (running)
{
RunningNrunnin(running);
//tradeClient.GetTradeHistory();
}
}
public void RunningNrunnin(bool running)
{
if (running)
{
Task task = new Task(() =>
{
while (running)
{
GetTradeHistory();
Thread.Sleep(2000);
}
});
task.Start();
}
}
Added Below
I would like to call a method over and over until the user creates a cancel request on a thread in the background. I currently had it so I can call a action (a counter) and update the GUI each second but when I try to do this same thing with a method call it executes only once.
// Here is the method I want to call continously until canceled
private async void HistoryTest()
{
cancellationToken = new CancellationTokenSource();
task = Task.Factory.StartNew(async () =>
{
while (true)
{
cancellationToken.Token.ThrowIfCancellationRequested();
await Client2.GetHistory();
await Task.Delay(2000);
}
}, cancellationToken.Token);
}
public async Task GetHistory()
{
try
{
var response = await Client.Service.GetDataAsync
(
ProductType.BtcUsd,
5,
1
);
}
catch(Exception)
{
throw;
}
}
I made a little console test app to test this so I had to change the method signatures (static) and can't use ButtonClick on a console. I simulated the button click by putting as sleep between the programatic "button click".
This might get you started.
private static bool isRunning = false;
private static int clickCounter = 0;
private static int iterationsCounter = 0;
static void Main(string[] args)
{
Console.WriteLine(“Start”);
for(int i = 0; i < 7; i++)
{
BtnTrade1_Buy_Click();
System.Threading.Thread.Sleep(1000);
}
Console.WriteLine(“END”);
}
private static async Task BtnTrade1_Buy_Click()
{
iterationsCounter = 0;
isRunning = !isRunning;
Console.WriteLine($"Ha: {isRunning} {clickCounter++}");
await RunningNrunnin();
}
private static async Task RunningNrunnin()
{
await Task.Run(() => Runit());
}
private static void Runit()
{
while (isRunning)
{
GetTradeHistory();
System.Threading.Thread.Sleep(100);
}
}
private static void GetTradeHistory()
{
Console.WriteLine($"Hello Test {iterationsCounter++}");
}
Of course you wouldn't need all the counters and the Console.WriteLine() stuff. They are there to allow you to visualize what is happening.
Let me know if you need more info.
You don't need to do anything else inside the BtnTrade1_Buy_Click event handler, beyond toggling the isRunning field:
private bool _isRunning;
private void BtnTrade1_Buy_Click(object sender, RoutedEventArgs e)
{
_isRunning = !_isRunning;
}
The Task that is getting the trade history in a loop, needs to be started only once. You could start it in the Window_Loaded event. Storing the Task in a private field is a good idea, in case you decide to await it at some point, but if you are handling the exceptions inside the task it's not necessary.
private void Window_Loaded(object sender, RoutedEventArgs e)
{
_ = StartTradeHistoryLoopAsync(); // Fire and forget
}
private async Task StartTradeHistoryLoopAsync()
{
while (true)
{
var delayTask = Task.Delay(2000);
if (_isRunning)
{
try
{
await Task.Run(() => GetTradeHistory()); // Run in the ThreadPool
//GetTradeHistory(); // Alternative: Run in the UI thread
}
catch (Exception ex)
{
// Handle the exception
}
}
await delayTask;
}
}
Don't forget to stop the task when the window is closed.
private void Window_Closed(object sender, EventArgs e)
{
_isRunning = false;
}
This will stop the calls to GetTradeHistory(), but will not stop the loop. You may need to add one more private bool field to control the loop itself:
while (_alive) // Instead of while (true)
I'm trying to find some solutions to my problem here, but with no result (or I just do not get them right) so if anyone could help / explain i will be really gratefull.
I'm just developing a tool for system administrators using Win Form and now I need to create a continuous ping on the selected machine which is running on the background. There is an indicator for Online status on UI which I need to edit with background ping. So right now I'm in this state:
Class A (Win form):
ClassB activeRelation = new ClassB();
public void UpdateOnline(Relation pingedRelation)
{
//There is many Relations at one time, but form shows Info only for one...
if (activeRelation == pingedRelation)
{
if (p_Online.InvokeRequired)
{
p_Online.Invoke(new Action(() =>
p_Online.BackgroundImage = (pingedRelation.Online) ? Properties.Resources.Success : Properties.Resources.Failure
));
}
else
{
p_Online.BackgroundImage = (pingedRelation.Online) ? Properties.Resources.Success : Properties.Resources.Failure;
}
}
}
//Button for tunring On/Off the background ping for current machine
private void Btn_PingOnOff_Click(object sender, EventArgs e)
{
Button btn = (sender is Button) ? sender as Button : null;
if (btn != null)
{
if (activeRelation.PingRunning)
{
activeRelation.StopPing();
btn.Image = Properties.Resources.Switch_Off;
}
else
{
activeRelation.StartPing(UpdateOnline);
btn.Image = Properties.Resources.Switch_On;
}
}
}
Class B (class thats represent relation to some machine)
private ClassC pinger;
public void StartPing(Action<Relation> action)
{
pinger = new ClassC(this);
pinger.PingStatusUpdate += action;
pinger.Start();
}
public void StopPing()
{
if (pinger != null)
{
pinger.Stop();
pinger = null;
}
}
Class C (background ping class)
private bool running = false;
private ClassB classb;
private Task ping;
private CancellationTokenSource tokenSource;
public event Action<ClassB> PingStatusUpdate;
public ClassC(ClassB classB)
{
this.classB = classB;
}
public void Start()
{
tokenSource = new CancellationTokenSource();
CancellationToken token = tokenSource.Token;
ping = PingAction(token);
running = true;
}
public void Stop()
{
if (running)
{
tokenSource.Cancel();
ping.Wait(); //And there is a problem -> DeadLock
ping.Dispose();
tokenSource.Dispose();
}
running = false;
}
private async Task PingAction(CancellationToken ct)
{
bool previousResult = RemoteTasks.Ping(classB.Name);
PingStatusUpdate?.Invoke(classB);
while (!ct.IsCancellationRequested)
{
await Task.Delay(pingInterval);
bool newResult = RemoteTasks.Ping(classB.Name);
if (newResult != previousResult)
{
previousResult = newResult;
PingStatusUpdate?.Invoke(classB);
}
}
}
So the problem is in deadlock when I cancel token and Wait() for task to complete -> it's still running, but While(...) in task is finished right.
You have a deadlock because ping.Wait(); blocks UI thread.
You should wait for task asynchronously using await.
So, if Stop() is event handler then change it to:
public async void Stop() // async added here
{
if (running)
{
tokenSource.Cancel();
await ping; // await here
ping.Dispose();
tokenSource.Dispose();
}
running = false;
}
If it is not:
public async Task Stop() // async added here, void changed to Task
{
if (running)
{
tokenSource.Cancel();
await ping; // await here
ping.Dispose();
tokenSource.Dispose();
}
running = false;
}
As mentioned by #JohnB async methods should have Async suffix so, the method should be named as StopAsync().
Similar problem and solution are explained here - Do Not Block On Async Code
You should avoid synchronous waiting on tasks, so you should always use await with tasks instead of Wait() or Result. Also, as pointed by #Fildor you should use async-await all the way to avoid such situations.
In an ASP Net Core 2 MVC app, I am using this BackGroundService (via IHostingService) with the below implementation to update singleton gauge objects for a real-time dashboard. However, I don't know of a good way to ensure I capture any exceptions thrown when the Update event is fired.
Note: I am aware of AppDomain.UnhandledException but find it to be more of a sledgehammer approach and would like something easier to maintain and scale.
Or, is there an entirely better way to periodically update data in a background task in ASP.NET Core 2?
public class GaugeUpdater : BackgroundService
{
private readonly List<IUpdateable> _updatables;
private Timer _timer;
public GaugeUpdater (IEnumerable<IUpdateable> updateables)
{
_updatables = updateables.ToList();
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
if (!stoppingToken.IsCancellationRequested)
{
await InitializeUpdateables();
SetTimer();
}
}
private void SetTimer()
{
const int intervalMilliseconds = 60_000;
var interval = new TimeSpan(0, 0, 0, 0, intervalMilliseconds);
_timer = new Timer(UpdateAll, null, interval, interval);
}
private async Task InitializeUpdateables()
{
var tasks = _updatables.Select(x => x.Initialize()).ToList();
await Task.WhenAll(tasks);
}
private async void UpdateAll(object state)
{
// TODO: Find way to handle exceptions, as awaiting async void makes it impossible for caller to catch.
// AppDomain.UnhandledException is possible but hard to maintain and handle in this scope.
_updatables.ForEach(async x => await x.Update());
}
}
async void can work for event handlers. Create and event and raise it with the timer. From there you should be able to await async tasks and handle exceptions
public class GaugeUpdater : BackgroundService {
private readonly List<IUpdateable> _updatables;
private Timer _timer;
public GaugeUpdater (IEnumerable<IUpdateable> updateables) {
_updatables = updateables.ToList();
Updating += OnUpdating; //Subscribe to event
}
private event EventHandler Updating = delegate { };
private async void OnUpdating(object sender, EventArgs args) {
try {
var tasks = _updatables.Select(x => x.Update());
await Task.WhenAll(tasks);
} catch {
//TODO: Logging???
}
}
private void UpdateAll(object state) {
Updating(this, EventArgs.Empty); //Raise event
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken) {
if (!stoppingToken.IsCancellationRequested) {
await InitializeUpdateables();
SetTimer();
}
}
private void SetTimer() {
const int intervalMilliseconds = 60_000;
var interval = new TimeSpan(0, 0, 0, 0, intervalMilliseconds);
_timer = new Timer(UpdateAll, null, interval, interval);
}
private async Task InitializeUpdateables() {
var tasks = _updatables.Select(x => x.Initialize()).ToList();
await Task.WhenAll(tasks);
}
}
I use awesomium to automate a site. I tried to use asynchronous programming, because I didn't want my GUI to freeze, but I have a problem at a event (a popup appear and I want to make some actions in this popup until I close it) when the application doesn't continue how I want. After the event is fired I want my application to continue with the event method (webc_ShowCreatedWebView and after with popupTwitter(method), but I find that when executing JavaScript code, the control returns in the While from the first method. How could I do that after the earnpoints method is called and the events is fired to finish the event and the method and after that the control return in the while.
private async void button4_Click(object sender, EventArgs e)
{
Twitter twitter = new Twitter(webView);
twitter.Login(webView);
webView.ShowCreatedWebView += webc_ShowCreatedWebView;
addmefast.Login(webView);
int i = 0;
while (i < 10)
{
Task earnpoints = EarnPoints(webView);
await earnpoints;
//Here i don't want to continue until EarnPoints method > webc_ShowCreatedWebView event > popupTwitter method it's finished.
i++;
}
}
public async Task EarnPoints(IWebView web)
{
web.Source = "http://addmefast.com/free_points/twitter".ToUri();
await Task.Delay(3000);
web.ExecuteJavascript("document.getElementsByClassName('single_like_button btn3-wrap')[0].click();"); //event fired: webc_ShowCreatedWebView
}
async void webc_ShowCreatedWebView(object sender, ShowCreatedWebViewEventArgs e)
{
WebView view = new WebView(e.NewViewInstance);
await popupTwitter(view);
}
async Task popupTwitter(WebView view)
{
Popupform FormTwitter = new Popupform(view);
FormTwitter.Show();
await Task.Delay(6000);
FormTwitter.Twitter();
await Task.Delay(2000);
FormTwitter.Close();
await Task.Delay(4000);
}
I also had problems implementing async methods with awesomium, but got it working.
First I made this wrapper. Have to be created on the main thread.
public class AsyncWebView
{
public static SynchronizationContext _synchronizationContext;
private readonly WebView _webView;
public AsyncWebView()
{
_synchronizationContext = SynchronizationContext.Current;
_webView = WebCore.CreateWebView(1024, 900);
}
public async Task Navigate(String url)
{
Debug.WriteLine("Navigating");
TaskCompletionSource<bool> tcs = new TaskCompletionSource<bool>();
FrameEventHandler handler = (sender, args) =>
{
Debug.WriteLine(args.Url);
if (!_webView.IsNavigating && !_webView.IsLoading)
tcs.SetResult(true);
};
_webView.LoadingFrameComplete += handler;
_synchronizationContext.Send(SetWebViewSource, url);
await tcs.Task;
_webView.LoadingFrameComplete -= handler;
Debug.WriteLine("Done");
}
private void SetWebViewSource(object url)
{
_webView.Source = new Uri((string)url);
}
}
Usage:
async Task test()
{
await webView.Navigate("http://www.nytimes.com");
Debug.WriteLine("All done");
}
Just make sure you have a SynchronizationContext where the AsyncWebView constructor is called from.