Timer in C#(1)

There are 3 different Timers in C#

1. System.Windows.Forms.Timer
2. System.Threading.Timer
3. System.Timers.Timer

I will introduce them separately

1. System.Windows.Forms.Timer

A Timer is used to raise an event at user-defined intervals. This Windows timer is designed for a single-threaded environment where UI threads are used to perform processing. It requires that the user code have a UI message pump available and always operate from the same thread, or marshal the call onto another thread.

When you use this timer, use the Tick event to perform a polling operation or to display a splash screen for a specified period of time. Whenever the Enabled property is set to true and the Interval property is greater than zero, the Tick event is raised at intervals based on the Interval property setting.

This class provides methods to set the interval, and to start and stop the timer.

2. System.Threading.Timer

Use a TimerCallback delegate to specify the method you want the Timer to execute. 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.

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). You can change these values, or disable the timer, using the Change method.

3. System.Timers.Timer
The Timer component is a server-based timer, which allows you to specify a recurring interval at which the Elapsed event is raised in your application. You can then handle this event to provide regular processing. For example, suppose you have a critical server that must be kept running 24 hours a day, 7 days a week. You could create a service that uses a Timer to periodically check the server and ensure that the system is up and running. If the system is not responding, the service could attempt to restart the server or notify an administrator.

The server-based Timer is designed for use with worker threads in a multithreaded environment. Server timers can move among threads to handle the raised Elapsed event, resulting in more accuracy than Windows timers in raising the event on time. For more information on server-based timers, see Introduction to Server-Based Timers[last part of this article].

The Timer component raises the Elapsed event, based on the value of the Interval property. You can handle this event to perform the processing you need. For example, suppose that you have an online sales application that continuously posts sales orders to a database. The service that compiles the instructions for shipping operates on a batch of orders rather than processing each order individually. You could use a Timer to start the batch processing every 30 minutes.

Server Timers, Windows Timers, and Thread Timers

 

There are three timer controls in Visual Studio and the .NET Framework:

• A server-based timer, which you can add to the Toolbox
• A Windows-based timer, which is always in the Toolbox
• A thread timer, which is available programmatically

The Windows-based timer is optimized for use in Windows Forms applications. The server-based timer is an update of the traditional timer that has been optimized to run in a server environment. The thread timer is a simple, lightweight timer that uses callback methods instead of events and is served by thread-pool threads.

There are two types of threads in Win32 architecture: UI threads, and worker threads. UI threads sit idle most of the time and wait for messages to arrive in their message loops. Once they receive a message, they handle it and then wait for the next message to arrive. Alternatively, worker threads are used to perform background processing and do not use message loops. Both the Windows timer and the server-based timer run using an Interval property. The interval of the thread timer is set in the Timer constructor. The timers are designed for different purposes, as evidenced by their handling of threads:

The Windows timer is designed for a single-threaded environment where UI threads are used to perform processing. The accuracy of Windows timers is limited to 55 milliseconds. These traditional timers require that the user code have a UI message pump available and always operate from the same thread, or marshal the call onto another thread. For a COM component, this would be detrimental to performance.

The server-based timer is designed for use with worker threads in a multi-threaded environment. Because they use a different architecture, server-based timers have the potential to be much more accurate than Windows timers. Server timers can move among threads to handle the raised events.

The thread timer is useful in scenarios where messages are not pumped on the thread. For example, the Windows-based timer relies on operating-system timer support, and if you are not pumping messages on the thread, the event associated with your timer will not occur. The thread timer is more useful in this case.

 

Ref:http://msdn.microsoft.com/en-us/magazine/cc164015.aspx

转载于:https://www.cnblogs.com/whyandinside/archive/2009/08/07/1541331.html