C# 的timer 与线程

有一次面试，面试官说卡顿怎么处理，我说多线程。多线程比timer好读。

好了，现在看看timer和线程的关系。

timer有3种

1.winform 下的timer。就是拖控件到UI上的那个timer.   

源文件在这个路径下C:\Windows\Microsoft.NET\Framework64\v4.0.30319

namespace System.Windows.Forms
{
    // 摘要:    实现按用户定义的时间间隔引发事件的计时器。 此计时器最宜用于 Windows 窗体应用程序中，并且必须在窗口中     使用。
    [DefaultEvent("Tick")]
    [DefaultProperty("Interval")][SRDescriptionAttribute("DescriptionTimer")][ToolboxItemFilter("System.Windows.Forms")]
    public class Timer : Component
}

 启动timer代码如下：  

[SRCategory("CatBehavior")]
    [DefaultValue(false)]
    [SRDescription("TimerEnabledDescr")]
    public virtual bool Enabled
    {
        get
        {
            if (this.timerWindow == null)
            {
                return this.enabled;
            }
            return this.timerWindow.IsTimerRunning;
        }
        set
        {
            lock (this.syncObj)
            {
                if (this.enabled != value)
                {
                    this.enabled = value;
                    if (!base.DesignMode)
                    {
                        if (value)
                        {
                            if (this.timerWindow == null)
                            {
                                this.timerWindow = new TimerNativeWindow(this);
                            }
                            this.timerRoot = GCHandle.Alloc(this);
                            this.timerWindow.StartTimer(this.interval);
                        }
                        else
                        {
                            if (this.timerWindow != null)
                            {
                                this.timerWindow.StopTimer();
                            }
                            if (this.timerRoot.IsAllocated)
                            {
                                this.timerRoot.Free();
                            }
                        }
                    }
                }
            }
        }
    }

 最终调用了this.timerWindow.StartTimer(this.interval); 源码如下。可见，最终调用的是系统的timer?系统是有定时器的。Ucos上，就有32个定时器，当然也可以开线程。他们是不同的概念。windows 也差不多吧。这些定时器应该与CPU有关。

public void StartTimer(int interval)
    {
        if (this._timerID == 0 && !this._stoppingTimer && this.EnsureHandle())
        {
            this._timerID = (int)SafeNativeMethods.SetTimer(new HandleRef(this, base.Handle), TimerNativeWindow.TimerID++, interval, IntPtr.Zero);
        }
    }

2.  public sealed class Timer : MarshalByRefObject, IDisposable    System.Threading.Timer

	public Timer(TimerCallback callback)
	{
		int dueTime = -1;
		int period = -1;
		StackCrawlMark stackCrawlMark = StackCrawlMark.LookForMyCaller;
		this.TimerSetup(callback, this, (uint)dueTime, (uint)period, ref stackCrawlMark);
	}

	[SecurityCritical]
	private void TimerSetup(TimerCallback callback, object state, uint dueTime, uint period, ref StackCrawlMark stackMark)
	{
		if (callback == null)
		{
			throw new ArgumentNullException("TimerCallback");
		}
		this.m_timer = new TimerHolder(new TimerQueueTimer(callback, state, dueTime, period, ref stackMark));
	}

	[SecurityCritical]
	internal static void Pause()
	{
		TimerQueue.Instance.Pause();
	}

	[SecurityCritical]
	internal static void Resume()
	{
		TimerQueue.Instance.Resume();
	}

这里是TimerQueue 队列的操作。既然在Threading 命名空间下，可能与线程有关。他在的dll 是 mscorlib.

3.  System.Timers.Timer，  在system.dll中。  只是对 System.Threading.Timer的封装。

	[TimersDescription("TimerEnabled")]
	[DefaultValue(false)]
	public bool Enabled
	{
		get
		{
			return this.enabled;
		}
		set
		{
			if (base.DesignMode)
			{
				this.delayedEnable = value;
				this.enabled = value;
			}
			else if (this.initializing)
			{
				this.delayedEnable = value;
			}
			else if (this.enabled != value)
			{
				if (!value)
				{
					if (this.timer != null)
					{
						this.cookie = null;
						this.timer.Dispose();
						this.timer = null;
					}
					this.enabled = value;
				}
				else
				{
					this.enabled = value;
					if (this.timer == null)
					{
						if (this.disposed)
						{
							throw new ObjectDisposedException(base.GetType().Name);
						}
						int num = (int)Math.Ceiling(this.interval);
						this.cookie = new object();
						this.timer = new System.Threading.Timer(this.callback, this.cookie, num, this.autoReset ? num : (-1));
					}
					else
					{
						this.UpdateTimer();
					}
				}
			}
		}
	}

4.使用：

void Application_Start(object sender, EventArgs e)
    {
        // 在应用程序启动时运行的代码
        if (timer != null)
        {
            timer.Stop();
            timer.Close();
            timer = null;
        }
        int Interval = 3600000;//6 hours 
        timer = new System.Timers.Timer(Interval);//十分钟  
        timer.Elapsed += SendSMS.Send_ticker;
        timer.Interval = Interval;
        timer.Enabled = true;
        timer.Start();
    }