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timers.md

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title description ms.date dev_langs helpviewer_keywords ms.assetid author
Timers
Learn what .NET timers to use in a multithreaded environment.
07/03/2018
csharp
vb
cpp
threading [.NET], timers
timers, about timers
7091500d-be18-499b-a942-95366ce185e5
pkulikov

Timers

.NET provides three timers to use in a multithreaded environment:

  • xref:System.Threading.Timer?displayProperty=nameWithType, which executes a single callback method on a xref:System.Threading.ThreadPool thread at regular intervals.
  • xref:System.Timers.Timer?displayProperty=nameWithType, which by default raises an event on a xref:System.Threading.ThreadPool thread at regular intervals.
  • xref:System.Threading.PeriodicTimer?displayProperty=nameWithType, which allows the caller to perform work after awaiting individual ticks of the timer.

Note

Some .NET implementations may include additional timers:

  • xref:System.Windows.Forms.Timer?displayProperty=nameWithType: a Windows Forms component that fires an event at regular intervals. The component has no user interface and is designed for use in a single-threaded environment.
  • xref:System.Web.UI.Timer?displayProperty=nameWithType: an ASP.NET component that performs asynchronous or synchronous web page postbacks at a regular interval.
  • xref:System.Windows.Threading.DispatcherTimer?displayProperty=nameWithType: a timer that is integrated into the xref:System.Windows.Threading.Dispatcher queue which is processed at a specified interval of time and at a specified priority.

The System.Threading.Timer class

The xref:System.Threading.Timer?displayProperty=nameWithType class enables you to continuously call a delegate at specified time intervals. You can also use this class to schedule a single call to a delegate in a specified time interval. The delegate is executed on a xref:System.Threading.ThreadPool thread.

When you create a xref:System.Threading.Timer?displayProperty=nameWithType object, you specify a xref:System.Threading.TimerCallback delegate that defines the callback method, an optional state object that is passed to the callback, the amount of time to delay before the first invocation of the callback, and the time interval between callback invocations. To cancel a pending timer, call the xref:System.Threading.Timer.Dispose%2A?displayProperty=nameWithType method.

The following example creates a timer that calls the provided delegate for the first time after one second (1000 milliseconds) and then calls it every two seconds. The state object in the example is used to count how many times the delegate is called. The timer is stopped when the delegate has been called at least 10 times.

[!code-cppSystem.Threading.Timer#2] [!code-csharpSystem.Threading.Timer#2] [!code-vbSystem.Threading.Timer#2]

For more information and examples, see xref:System.Threading.Timer?displayProperty=nameWithType.

The System.Timers.Timer class

Another timer that can be used in a multithreaded environment is xref:System.Timers.Timer?displayProperty=nameWithType that by default raises an event on a xref:System.Threading.ThreadPool thread.

When you create a xref:System.Timers.Timer?displayProperty=nameWithType object, you may specify the time interval in which to raise an xref:System.Timers.Timer.Elapsed event. Use the xref:System.Timers.Timer.Enabled%2A property to indicate if a timer should raise an xref:System.Timers.Timer.Elapsed event. If you need an xref:System.Timers.Timer.Elapsed event to be raised only once after the specified interval has elapsed, set the xref:System.Timers.Timer.AutoReset%2A to false. The default value of the xref:System.Timers.Timer.AutoReset%2A property is true, which means that an xref:System.Timers.Timer.Elapsed event is raised regularly at the interval defined by the xref:System.Timers.Timer.Interval%2A property.

For more information and examples, see xref:System.Timers.Timer?displayProperty=nameWithType.

The System.Threading.PeriodicTimer class

The xref:System.Threading.PeriodicTimer?displayProperty=nameWithType class enables you to await individual ticks of a specified interval, performing work after calling xref:System.Threading.PeriodicTimer.WaitForNextTickAsync%2A?displayProperty=nameWithType.

When you create a xref:System.Threading.PeriodicTimer?displayProperty=nameWithType object, you specify a xref:System.TimeSpan that determines the length of time between each tick of the timer. Instead of passing a callback or setting an event handler as in the previous timer classes, you perform work directly in scope, awaiting xref:System.Threading.PeriodicTimer.WaitForNextTickAsync%2A to advance the timer by the specified interval.

The xref:System.Threading.PeriodicTimer.WaitForNextTickAsync%2A method returns a ValueTask<bool>; true upon successful firing of the timer, and false when the timer has been canceled by calling xref:System.Threading.PeriodicTimer.Dispose%2A?displayProperty=nameWithType. xref:System.Threading.PeriodicTimer.WaitForNextTickAsync%2A optionally accepts a xref:System.Threading.CancellationToken, which results in a xref:System.Threading.Tasks.TaskCanceledException when a cancellation has been requested.

For more information, see xref:System.Threading.PeriodicTimer?displayProperty=nameWithType.

See also

  • xref:System.Threading.Timer?displayProperty=nameWithType
  • xref:System.Timers.Timer?displayProperty=nameWithType
  • xref:System.Threading.PeriodicTimer?displayProperty=nameWithType
  • Threading Objects and Features