asp.net 定時器

在使用WinForm編程中，我們可以使用定時器實現規定周期的定時工作進行操作，而在ASP.Net 如何操作，卻是個問題。

而在ASP.Net Forums中有很好的例子，定時器應用如下：
1. 更新論壇統計信息
2. 定時索引指定條數的帖子
3. 定時群發隊列中的郵件

Forums中對定時器的調用是放在自定義HttpModule的Init方法中（如果您沒有使用HttpModule，也可以在Globals.ASPx中的Application_OnStart 中調用定時器）。

      // 定時器 
        static Timer statsTimer; 
        static Timer emailTimer; 
 
        // 定時間隔 
        private long EmailInterval = ForumConfiguration.GetConfig().ThreadIntervalEmail * 60000; 
        private long StatsInterval = ForumConfiguration.GetConfig().ThreadIntervalStats * 60000; 
 
        public String ModuleName {  
            get { return "ForumsHttpModule"; }  
        }     
 
 
        // ********************************************************************* 
        //  ForumsHttpModule 
        // 
        /**//// <summary> 
        /// Initializes the HttpModule and performs the wireup of all application 
        /// events. 
        /// </summary> 
        /// <param name="application">Application the module is being run for</param> 
        public void Init(HttpApplication application) {  
 
            // Wire-up application events 
            // 
   &nbsp;        // 略去其他代碼 
             
            ForumConfiguration forumConfig = ForumConfiguration.GetConfig(); 
 
            // 如果使用定時器並且定時器還沒初始化 
            if( forumConfig != null 
            &&  forumConfig.IsBackgroundThreadingDisabled == false ) { 
                if (emailTimer == null) 
                    // 新建定時器 
                    // 新建一個TimerCallback委托，具體要執行的方法在ScheduledWorkCallbackEmailInterval中 
                    emailTimer = new Timer(new TimerCallback(ScheduledWorkCallbackEmailInterval), application.Context, EmailInterval, EmailInterval); 
 
                if( forumConfig.IsIndexingDisabled == false  
                &&    statsTimer == null ) { 
                    statsTimer = new Timer(new TimerCallback(ScheduledWorkCallbackStatsInterval), application.Context, StatsInterval, StatsInterval); 
            } 
        } 
        } 
 
        /**//// <summary> 
        /// 釋放定時器&nbsp;
        /// </summary> 
        public void Dispose() { 
            statsTimer = null; 
            emailTimer = null; 
        } 
 
        Timer Callbacks#region Timer Callbacks 
        /**//// <summary> 
        /// 定時發送隊列中待發送的郵件 
        /// </summary> 
        private void ScheduledWorkCallbackEmailInterval (object sender) { 
            try { 
                // 當處理郵件時暫停定時器 
                emailTimer.Change( System.Threading.Timeout.Infinite, EmailInterval ); 
 
                // 發送隊列中的郵件 
                // 
                Emails.SendQueuedEmails( (HttpContext) sender); 
 
 
                // 更新匿名用戶 
                // 
                Users.UpdateAnonymousUsers( (HttpContext) sender); 
            } 
            catch( Exception e ) {  
             

;  ForumException fe = new ForumException( ForumExceptionType.EmailUnableToSend, "Scheduled Worker Thread failed.", e ); 
                fe.Log(); 
            } 
            finally { 
                // 重新啟動定時器 
                emailTimer.Change( EmailInterval, EmailInterval ); 
            } 
        } 
 
        /**//// <summary> 
        /// 定時索引帖子和定時更新論壇統計信息 
        /// </summary> 
        private void ScheduledWorkCallbackStatsInterval(object sender) { 
            try { 
                // 休眠定時器 
                statsTimer.Change( System.Threading.Timeout.Infinite, StatsInterval ); 
 
                // 每次索引100篇帖子 
                // 
                Search.IndexPosts( (HttpContext) sender, 100); 
 
                // 更新論壇統計信息 
                SiteStatistics.LoadSiteStatistics( (HttpContext) sender, true, 1 ); 
            }

            catch( Exception e ) { 
                ForumException fe = new ForumException( ForumExceptionType.UnknownError, "Failure performing scheduled statistics maintenance.", e ); 
                fe.Log(); 
            } 
            finally { 
                // 喚醒定時器 
                statsTimer.Change( StatsInterval, StatsInterval); 
            } 
        } 
        #endregion