CreateWaitableTimer和SetWaitableTimer函数

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用户感觉到软件的好用，就是可以定时地做一些工作，而不需要人参与进去。比如每天定时地升级病毒库，定时地下载电影，定时地更新游戏里的人物。要想实现这些功能，就可以使用定时器的API函数CreateWaitableTimer和SetWaitableTimer来实现了，这对API函数创建的时钟是比较精确的，可以达到100倍的10亿分之一秒。

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// CreateWaitableTimer
// C#
[DllImport("kernel32.dll")]
static extern IntPtr CreateWaitableTimer(IntPtr lpTimerAttributes, bool bManualReset, string lpTimerName);

[DllImport("kernel32.dll")]
public static extern IntPtr CreateWaitableTimer(IntPtr lpTimerAttributes, bool bManualReset,
                         string lpTimerName);

[DllImport("kernel32.dll")]
public static extern bool SetWaitableTimer(IntPtr hTimer, [In] ref long pDueTime,
                        int lPeriod, TimerAPCProc pfnCompletionRoutine,
                        IntPtr lpArgToCompletionRoutine, bool fResume);

[DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
public static extern Int32 WaitForSingleObject(IntPtr handle, int milliseconds);
public static uint INFINITE = 0xFFFFFFFF;

// SetWaitableTimer
[DllImport("kernel32.dll")]
static extern bool SetWaitableTimer(IntPtr hTimer, [In] ref long pDueTime,
   int lPeriod, TimerCompleteDelegate pfnCompletionRoutine,
   IntPtr lpArgToCompletionRoutine, bool fResume);

函数CreateWaitableTimer和SetWaitableTimer声明如下：

lpTimerAttributes是设置定时器的属性。

bManualReset是是否手动复位。

lpTimerName是定时器的名称。

hTimer是定时器的句柄。

lpDueTime是设置定时器时间间隔，当设置为正值是绝对时间；当设置为负数是相对时间。

lPeriod是周期。

pfnCompletionRoutine是设置回调函数。

lpArgToCompletionRoutine是传送给回调函数的参数。

fResume是设置系统是否自动恢复。

调用函数的例子如下：

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// CreateWaitableTimer
private IntPtr handle;

private void shutdownToolStripMenuItem_Click(object sender, EventArgs e)
{
     DateTime dt = DateTime.Now;
     dt = dt.AddSeconds(30.0);
     long duetime = dt.ToFileTime();

     handle = Win32.PowerManagement.CreateWaitableTimer(IntPtr.Zero, true, "");
     Win32.PowerManagement.SetWaitableTimer(handle, ref duetime, 0, null, IntPtr.Zero, true);

     Thread t = new Thread(new ThreadStart(this.NewThread));
     t.Start();
}

private void NewThread()
{
     int ret = Win32.PowerManagement.WaitForSingleObject(handle, (int)Win32.PowerManagement.INFINITE);
     MessageBox.Show("Wait object"); // ret = 0x00000000L here
}

// SetWaitableTimer
// Class that sets a WIN32 WaitableTimer. The timer will wake up the PC if the PC
// is in standby or hibernation mode.
class WaitableTimer
{
    public delegate void TimerSetDelegate();
    public delegate void TimerCompleteDelegate();

    public event TimerSetDelegate OnTimerSet;
    public event TimerCompleteDelegate OnTimerCompleted;

    [DllImport("kernel32.dll")]
    static extern IntPtr CreateWaitableTimer(IntPtr lpTimerAttributes, bool bManualReset, string lpTimerName);

    [DllImport("kernel32.dll")]
    static extern bool SetWaitableTimer(IntPtr hTimer, [In] ref long ft, int lPeriod, TimerCompleteDelegate pfnCompletionRoutine, IntPtr  pArgToCompletionRoutine, bool fResume);

    [DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
    static extern Int32 WaitForSingleObject(IntPtr Handle, uint Wait);

    [DllImport("kernel32.dll")]
    static extern bool CancelWaitableTimer(IntPtr hTimer);

    [DllImport("kernel32.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi, CharSet = CharSet.Auto)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool CloseHandle(IntPtr hObject);

    private IntPtr handle;
    private uint INFINITE = 0xFFFFFFFF;

    public void SetTimer(long Interval)
    {
        // Creating the timer delegate
        //
        TimerCompleteDelegate TimerComplete = new TimerCompleteDelegate(TimerCompleted);
        TimerSetDelegate TimerSet = new TimerSetDelegate(TimerIsSet);

        // Creating the timer
        //
        Console.WriteLine("Creating WaitableTimer");
        handle = CreateWaitableTimer(IntPtr.Zero, true, "WaitableTimer");
        Console.WriteLine("Last Error = " + Marshal.GetLastWin32Error().ToString());

        // Setting up the timer, the long Interval value needs to be negative if 
        // you want to set up a delay in milliseconds. ie 
        // if Interval = -60000000 the timer will expire in 1 minute. Once expired it runs the 
        // TimerComplete delegate
        //
        Console.WriteLine("Setting WaitableTimer");
        SetWaitableTimer(handle, ref Interval, 0, TimerComplete, IntPtr.Zero, true);
        Console.WriteLine("Last Error = " + Marshal.GetLastWin32Error().ToString()); // The error may be 1004 (Invalid flags), this is not critical
        Console.WriteLine("Timer set @ " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss"));

        // Starting a new thread which waits for the WaitableTimer to expire
        //
        Thread t_Wait = new Thread(new ThreadStart(WaitTimer));
        t_Wait.Start();

        // Raising Event Timer Set
        //
        if (OnTimerSet != null)
        {
            OnTimerSet();
        }
    }

    private void WaitTimer()
    {
        // Waiting for the timer to expire
        //
        if (WaitForSingleObject(handle, INFINITE) != 0)
        {
            Console.WriteLine("Last Error = " + Marshal.GetLastWin32Error().ToString());
        }
        else
        {
            Console.WriteLine("Timer expired @ " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss"));
        }

        // Closing the timer
        //
        CloseHandle(handle);

        // Raising event Timer Completed
        //
        if (OnTimerCompleted != null)
        {
            OnTimerCompleted();
        }
    }

    private void TimerCompleted()
    {
        // Routine executed once the timer has expired. This is executed independently of the 
        // program calling this class implementation of the OnTimerCompleted Event
        //
        Console.WriteLine("Timer is complete in the class");
    }

    private void TimerIsSet()
    {
        Console.WriteLine("Timer is set in the class");
    }
}