.NET System.Timers.Timer的原理和使用(开发定时执行程序)

概述(来自MSDN)

Timer 组件是基于服务器的计时器，它使您能够指定在应用程序中引发 Elapsed 事件的周期性间隔。然后可以操控此事件以提供定期处理。例如，假设您有一台关键性服务器，必须每周 7 天、每天 24 小时都保持运行。可以创建一个使用 Timer 的服务，以定期检查服务器并确保系统开启并在运行。如果系统不响应，则该服务可以尝试重新启动服务器或通知管理员。

基于服务器的 Timer 是为在多线程环境中用于辅助线程而设计的。服务器计时器可以在线程间移动来处理引发的 Elapsed 事件，这样就可以比 Windows 计时器更精确地按时引发事件。

基于 Interval 属性的值，Timer 组件引发 Elapsed 事件。可以处理该事件以执行所需的处理。例如，假设您有一个联机销售应用程序，它不断向数据库发送销售订单。编译发货指令的服务分批处理订单，而不是分别处理每个订单。可以使用 Timer 每 30 分钟启动一次批处理。

注意

当 AutoReset设置为false时，Timer只在第一个Interval过后引发一次Elapsed事件。若要保持以Interval时间间隔引发 Elapsed 事件，请将AutoReset设置为true。 
Elapsed事件在ThreadPool线程上引发。如果Elapsed事件的处理时间比Interval长，在另一个hreadPool线程上将会再次引发此事件。因此，事件处理程序应当是可重入的。

注意

在一个线程调用 Stop 方法或将 Enabled 属性设置为 false 的同时，可在另一个线程上运行事件处理方法。这可能导致在计时器停止之后引发 Elapsed 事件。Stop 方法的示例代码演示了一种避免此争用条件的方法。 
如果和用户界面元素（如窗体或控件）一起使用 Timer，请将包含有 Timer 的窗体或控件赋值给SynchronizingObject 属性，以便将此事件封送到用户界面线程中。 Timer 在运行时是不可见的。

 

几点说明

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private System.Timers.Timer _TestTimerEvent= new Timer();

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1、默认的周期是0.1秒执行一次；

2、AutoReset的初始值为true.

3、它的timer机制和System.Threading.Timer 原理是一样的。

4、每次周期(Timer)运行一次会新起一个线程。

5、如果Elapsed事件的处理时间比Interval长，它每个周期执行都会新起一个线程，这个线程的执行时间不受interval的限定，可以比interval长，因为一个新周期执行，又会新起一个线程，Timer起的线程周期就是事件处理时间。

我们来看它的实现代码.（.net framework 提供的）.

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//------------------------------------------------------------------------------

// <copyright file="Timer.cs" company="Microsoft">

//     Copyright (c) Microsoft Corporation.  All rights reserved.

// </copyright>

//-----------------------------------------------------------------------------

 

namespace System.Timers {

  

    using System.Runtime.InteropServices;

    using System.Security;

    using System.Security.Permissions;

    using System.Threading;

    using System.ComponentModel;

    using System.ComponentModel.Design;

    using System;

    using Microsoft.Win32;

    using Microsoft.Win32.SafeHandles;

 

    /// <devdoc>

    ///    <para>Handles recurring events in an application.</para>

    /// </devdoc>

    [

    DefaultProperty("Interval"),

    DefaultEvent("Elapsed"),

    HostProtection(Synchronization=true, ExternalThreading=true)

    ]

    public class Timer : Component, ISupportInitialize {

        private double interval;

        private bool  enabled;

        private bool initializing;

        private bool delayedEnable;

        private ElapsedEventHandler onIntervalElapsed;

        private bool autoReset;

        private ISynchronizeInvoke synchronizingObject;

        private bool disposed;

        private System.Threading.Timer timer;

        private TimerCallback callback;

        private Object cookie;

 

        /// <devdoc>

        /// <para>Initializes a new instance of the <see cref='System.Timers.Timer'/> class, with the properties

        ///    set to initial values.</para>

        /// </devdoc>

        public Timer()

        :base() {

            interval = 100;

            enabled = false;

            autoReset = true;

            initializing = false;

            delayedEnable = false;

            callback = new TimerCallback(this.MyTimerCallback);

        }

  

        /// <devdoc>

        ///    <para>

        ///       Initializes a new instance of the <see cref='System.Timers.Timer'/> class, setting the <see cref='System.Timers.Timer.Interval'/> property to the specified period.

        ///    </para>

        /// </devdoc>

        public Timer(double interval)

        :this() {

            if (interval <= 0)

                throw new ArgumentException(SR.GetString(SR.InvalidParameter,"interval", interval));

 

            int i = (int)Math.Ceiling(interval);

            if( i < 0) {

                throw new ArgumentException(SR.GetString(SR.InvalidParameter,"interval", interval));

            }

  

            this.interval = interval;

        }

  

        /// <devdoc>

        /// <para>Gets or sets a value indicating whether the Timer raises the Tick event each time the specified

        /// Interval has elapsed,

        ///    when Enabled is set to true.</para>

        /// </devdoc>

        [Category("Behavior"),  TimersDescription(SR.TimerAutoReset), DefaultValue(true)]

        public bool AutoReset {

            get {

                return this.autoReset;

            }

  

            set {

                if (DesignMode)

                     this.autoReset = value;

                else if (this.autoReset != value) {

                     this.autoReset = value;

                    if( timer != null) {

                         UpdateTimer();

                    }

                }

            }

        }

 

        /// <devdoc>

        /// <para>Gets or sets a value indicating whether the <see cref='System.Timers.Timer'/>

        /// is able

        /// to raise events at a defined interval.</para>

        /// </devdoc>

        //[....] - The default value by design is false, don't change it.

        [Category("Behavior"), TimersDescription(SR.TimerEnabled), DefaultValue(false)]

        public bool Enabled {

            get {

                return this.enabled;

            }

  

            set {

                if (DesignMode) {

                    this.delayedEnable = value;

                    this.enabled = value;

                }

                else if (initializing)

                    this.delayedEnable = value;

                else if (enabled != value) {

                    if (!value) {

                        if( timer != null) {

                            cookie = null;

                            timer.Dispose();

                            timer = null;

                        }

                        enabled = value;

                    }

                    else {

                        enabled = value;

                        if( timer == null) {

                            if (disposed) {

                                throw new ObjectDisposedException(GetType().Name);

                            }

 

                            int i = (int)Math.Ceiling(interval);

                            cookie = new Object();

                            timer = new System.Threading.Timer(callback, cookie, i, autoReset? i:Timeout.Infinite);

                        }

                        else {

                            UpdateTimer();

                        }

                    }

 

                }

          }

        }

  

  

        private void UpdateTimer() {

            int i = (int)Math.Ceiling(interval);

            timer.Change(i, autoReset? i :Timeout.Infinite );

        }

 

        /// <devdoc>

        ///    <para>Gets or

        ///       sets the interval on which

        ///       to raise events.</para>

        /// </devdoc>

        [Category("Behavior"), TimersDescription(SR.TimerInterval), DefaultValue(100d), RecommendedAsConfigurable(true)]

        public double Interval {

            get {

                return this.interval;

            }

 

            set {

                if (value <= 0)

                    throw new ArgumentException(SR.GetString(SR.TimerInvalidInterval, value, 0));

  

                interval = value;

                if (timer != null) {

                    UpdateTimer();

                }

            }

        }

  

 

        /// <devdoc>

        /// <para>Occurs when the <see cref='System.Timers.Timer.Interval'/> has

        ///    elapsed.</para>

        /// </devdoc>

        [Category("Behavior"), TimersDescription(SR.TimerIntervalElapsed)]

        public event ElapsedEventHandler Elapsed {

            add {

                onIntervalElapsed += value;

            }

            remove {

                onIntervalElapsed -= value;

            }

        }

  

        /// <devdoc>

        ///    <para>

        ///       Sets the enable property in design mode to true by default.

        ///    </para>

        /// </devdoc>

        /// <internalonly/>

        public override ISite Site {

            set {

                base.Site = value;

                if (this.DesignMode)

                    this.enabled=true;

            }

 

            get {

                return base.Site;

            }

        }

  

 

        /// <devdoc>

        ///    <para>Gets or sets the object used to marshal event-handler calls that are issued when

        ///       an interval has elapsed.</para>

        /// </devdoc>

        [

        Browsable(false),

        DefaultValue(null),

        TimersDescription(SR.TimerSynchronizingObject)

        ]

        public ISynchronizeInvoke SynchronizingObject {

            get {

                if (this.synchronizingObject == null && DesignMode) {

                    IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));

                    if (host != null) {

                        object baseComponent = host.RootComponent;

                        if (baseComponent != null && baseComponent is ISynchronizeInvoke)

                            this.synchronizingObject = (ISynchronizeInvoke)baseComponent;

                    }

                }

  

                return this.synchronizingObject;

            }

 

            set {

                this.synchronizingObject = value;

            }

        }

  

        /// <devdoc>

        ///    <para>

        ///       Notifies

        ///       the object that initialization is beginning and tells it to stand by.

        ///    </para>

        /// </devdoc>

        public void BeginInit() {

            this.Close();

            this.initializing = true;

        }

 

        /// <devdoc>

        ///    <para>Disposes of the resources (other than memory) used by

        ///       the <see cref='System.Timers.Timer'/>.</para>

        /// </devdoc>

        public void Close() {

            initializing = false;

            delayedEnable = false;

            enabled = false;

 

            if (timer != null ) {

                timer.Dispose();

                timer = null;

            }

        }

 

        /// <internalonly/>

        /// <devdoc>

        /// </devdoc>

        protected override void Dispose(bool disposing) {

            Close();

            this.disposed = true;

            base.Dispose(disposing);

        }

 

        /// <devdoc>

        ///    <para>

        ///       Notifies the object that initialization is complete.

        ///    </para>

        /// </devdoc>

        public void EndInit() {

            this.initializing = false;

            this.Enabled = this.delayedEnable;

        }

  

        /// <devdoc>

        /// <para>Starts the timing by setting <see cref='System.Timers.Timer.Enabled'/> to <see langword='true'/>.</para>

        /// </devdoc>

        public void Start() {

            Enabled = true;

        }

  

        /// <devdoc>

        ///    <para>

        ///       Stops the timing by setting <see cref='System.Timers.Timer.Enabled'/> to <see langword='false'/>.

        ///    </para>

        /// </devdoc>

        public void Stop() {

            Enabled = false;

        }

  

        private void MyTimerCallback(object state) {

            // System.Threading.Timer will not cancel the work item queued before the timer is stopped.

            // We don't want to handle the callback after a timer is stopped.

            if( state != cookie) {

                return;

            }

 

            if (!this.autoReset) {

                enabled = false;

            }

  

            FILE_TIME filetime = new FILE_TIME();

            GetSystemTimeAsFileTime(ref filetime);

            ElapsedEventArgs elapsedEventArgs = new ElapsedEventArgs(filetime.ftTimeLow, filetime.ftTimeHigh);

            try {

                // To avoid ---- between remove handler and raising the event

                ElapsedEventHandler intervalElapsed = this.onIntervalElapsed;

                if (intervalElapsed != null) {

                    if (this.SynchronizingObject != null &&this.SynchronizingObject.InvokeRequired)

                        this.SynchronizingObject.BeginInvoke(intervalElapsed,new object[]{this, elapsedEventArgs});

                    else

                       intervalElapsed(this,  elapsedEventArgs);

                }

            }

            catch {

            }

        }

 

        [StructLayout(LayoutKind.Sequential)]

        internal struct FILE_TIME {

            internal int ftTimeLow;

            internal int ftTimeHigh;

        }

 

        [DllImport(ExternDll.Kernel32), SuppressUnmanagedCodeSecurityAttribute()]

        internal static extern void GetSystemTimeAsFileTime(ref FILE_TIME lpSystemTimeAsFileTime);      

    }

}

  

 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.  

在初始化的时候它的代码实现是这样的.

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public Timer()

:base() {

    interval = 100;

    enabled = false;

    autoReset = true;

    initializing = false;

    delayedEnable = false;

    callback = new TimerCallback(this.MyTimerCallback);

}

 

 

而如果你是这样的话

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public Timer(double interval)

       :this() {

           if (interval <= 0)

               throw new ArgumentException(SR.GetString(SR.InvalidParameter,"interval", interval));

 

           int i = (int)Math.Ceiling(interval);

           if( i < 0) {

               throw new ArgumentException(SR.GetString(SR.InvalidParameter,"interval", interval));

           }

 

           this.interval = interval;

       }

 

 

你就需要再设置下AutoReset = True;

 

我们加载事件的Elapsed的代码实现是这样的.

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/// <devdoc>

/// <para>Occurs when the <see cref='System.Timers.Timer.Interval'/> has

///    elapsed.</para>

/// </devdoc>

[Category("Behavior"), TimersDescription(SR.TimerIntervalElapsed)]

public event ElapsedEventHandler Elapsed {

    add {

        onIntervalElapsed += value;

    }

    remove {

        onIntervalElapsed -= value;

    }

}

 

 

对它的基本原理有一定了解后，我们开始写一个简单的实现程序。

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using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading;

using Timer = System.Timers.Timer;

using System.Timers;

 

namespace TestMultipleThread

{

 

    public class ThreadWork

    {

        private System.Timers.Timer _TestTimerEvent;

 

        public void StartWork()

        {

            _TestTimerEvent = new Timer();

            _TestTimerEvent.Elapsed += Sum;

            _TestTimerEvent.Start();

        }

 

        public static object lockobject = new object();

 

 

        private void Sum(object sender, ElapsedEventArgs e)

        {

            Console.WriteLine(string.Format("this is thread ID {0}  execute", Thread.CurrentThread.ManagedThreadId));

            for (int i = 0; i < 10000; i++)

            {

                Thread.Sleep(10);

            }

        }

    }

 

    class Program

    {

        public static void Main()

        {

            ThreadWork threadWork = new ThreadWork();

            ThreadStart myThreadDelegate = new ThreadStart(threadWork.StartWork);

            Thread myThread = new Thread(myThreadDelegate);

            myThread.Start();

 

            Thread.Sleep(1000000);

        }

    }

}

 

 

查看的运行结果是:

 

我们看下执行的线程数有多少

 

能说明的一个问题就是在timer每次执行时都会新起一个线程来执行。

 

作者：spring yang

出处：http://www.cnblogs.com/springyangwc/

本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。