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Definition

Provides a mechanism for executing a method on a thread pool thread at specified intervals. This class cannot be inherited.

Attributes

Examples

The following example defines a StatusChecker class that includes a CheckStatus method whose signature is the same as the TimerCallback delegate. The state argument of the CheckStatus method is an AutoResetEvent object that is used to synchronize the application thread and the thread pool thread that executes the callback delegate. The StatusChecker class also includes two state variables:

invokeCount
Indicates the number of times the callback method has been invoked.

maxCount
Determines the maximum number of times the callback method should be invoked.

The application thread creates the timer, which waits one second and then executes the CheckStatus callback method every 250 milliseconds. The application thread then blocks until the AutoResetEvent object is signaled. When the CheckStatus callback method executes maxCount times, it calls the AutoResetEvent.Set method to set the state of the AutoResetEvent object to signaled. The first time this happens, the application thread calls the Change(Int32, Int32) method so that the callback method now executes every half second. It once again blocks until the AutoResetEvent object is signaled. When this happens, the timer is destroyed by calling its Dispose method, and the application terminates.

Remarks

Use a TimerCallback delegate to specify the method you want the Timer to execute. The signature of the TimerCallback delegate is:

The timer delegate is specified when the timer is constructed, and cannot be changed. The method does not execute on the thread that created the timer; it executes on a ThreadPool thread supplied by the system.

Tip

.NET includes several timer classes, each of which offers different functionality:

• System.Timers.Timer, which fires an event and executes the code in one or more event sinks at regular intervals. The class is intended for use as a server-based or service component in a multithreaded environment; it has no user interface and is not visible at runtime.
• System.Threading.Timer, which executes a single callback method on a thread pool thread at regular intervals. The callback method is defined when the timer is instantiated and cannot be changed. Like the System.Timers.Timer class, this class is intended for use as a server-based or service component in a multithreaded environment; it has no user interface and is not visible at runtime.
• System.Windows.Forms.Timer (.NET Framework only), a Windows Forms component that fires an event and executes the code in one or more event sinks at regular intervals. The component has no user interface and is designed for use in a single-threaded environment; it executes on the UI thread.
• System.Web.UI.Timer (.NET Framework only), an ASP.NET component that performs asynchronous or synchronous web page postbacks at a regular interval.
• System.Windows.Threading.DispatcherTimer, a timer that's integrated into the Dispatcher queue. This timer is processed with a specified priority at a specified time interval.

When you create a timer, you can specify an amount of time to wait before the first execution of the method (due time), and an amount of time to wait between subsequent executions (period). The Timer class has the same resolution as the system clock. This means that if the period is less than the resolution of the system clock, the TimerCallback delegate will execute at intervals defined by the resolution of the system clock, which is approximately 15 milliseconds on Windows 7 and Windows 8 systems. You can change the due time and period, or disable the timer, by using the Change method.

Note

As long as you are using a Timer, you must keep a reference to it. As with any managed object, a Timer is subject to garbage collection when there are no references to it. The fact that a Timer is still active does not prevent it from being collected.

When a timer is no longer needed, use the Dispose method to free the resources held by the timer. Note that callbacks can occur after the Dispose() method overload has been called, because the timer queues callbacks for execution by thread pool threads. You can use the Dispose(WaitHandle) method overload to wait until all callbacks have completed.

The callback method executed by the timer should be reentrant, because it is called on ThreadPool threads. The callback can be executed simultaneously on two thread pool threads if the timer interval is less than the time required to execute the callback, or if all thread pool threads are in use and the callback is queued multiple times.

Note

System.Threading.Timer is a simple, lightweight timer that uses callback methods and is served by thread pool threads. It is not recommended for use with Windows Forms, because its callbacks do not occur on the user interface thread. System.Windows.Forms.Timer is a better choice for use with Windows Forms. For server-based timer functionality, you might consider using System.Timers.Timer, which raises events and has additional features.

Task Timer App

Constructors

Properties

Free Task Timer

Task Timer For Kids

Methods

Extension Methods

Applies to

Intermatic Astronomical Time Clock Manual

Thread Safety

This type is thread safe.

Task Timer Chrome

See also