多线程编程(15) - 多线程同步之 WaitableTimer (等待定时器对象)[续]

本次专门研究下 SetWaitableTimer 的第二个参数(起始时间).
它有正值、负值、0值三种情况, 前面已用过 0值.
先学习负值(相对时间), 也就是从当前算起隔多长时间开始执行.

这个相对时间是以 1/100 纳秒为单位的, 譬如赋值 3*10000000 相当于 3 秒.

1 s(秒) = 1,000             ms(毫秒);

1 s(秒) = 1,000,000         µs(微妙);

1 s(秒) = 1,000,000,000     ns(纳秒);

1 s(秒) = 1,000,000,000,000 ps(皮秒);


 
   

本例效果图:

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代码文件:

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    procedure Button1Click(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  f: Integer;

  hWaitableTimer: THandle;



function MyThreadFun(p: Pointer): DWORD; stdcall;

var

  i,y: Integer;

begin

  Inc(f);

  y := 20 * f;



  if WaitForSingleObject(hWaitableTimer, INFINITE) = WAIT_OBJECT_0 then

  begin

    for i := 0 to 1000 do

    begin

      Form1.Canvas.Lock;

      Form1.Canvas.TextOut(20, y, IntToStr(i));

      Form1.Canvas.Unlock;

      Sleep(1);

    end;

  end;

  Result := 0;

end;



procedure TForm1.Button1Click(Sender: TObject);

var

  ThreadID: DWORD;

  DueTime: Int64;

begin

  hWaitableTimer := CreateWaitableTimer(nil, True, nil);

  DueTime := -3*10000000; {3秒钟后执行}

  SetWaitableTimer(hWaitableTimer, DueTime, 0, nil, nil, False);



  Repaint; f := 0;

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  CloseHandle(hWaitableTimer);

end;



end.


 
   

窗体文件:

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object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 116

  ClientWidth = 179

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  OnDestroy = FormDestroy

  PixelsPerInch = 96

  TextHeight = 13

  object Button1: TButton

    Left = 96

    Top = 83

    Width = 75

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

end


 
   

当我们需要一个绝对时间时, 譬如 2009-2-18 13:10:5, 函数需要的 Int64 值应该是个 TFileTime 格式的时间.

先看三种相关时间类型(TFileTime、TSystemTime、TDateTime)的定义:

---

TFileTime(又名 FILETIME 或 _FILETIME)

_FILETIME = record

  dwLowDateTime: DWORD;

  dwHighDateTime: DWORD;

end;



TSystemTime(又名 SYSTEMTIME 或 _SYSTEMTIME)

_SYSTEMTIME = record

  wYear: Word;

  wMonth: Word;

  wDayOfWeek: Word;

  wDay: Word;

  wHour: Word;

  wMinute: Word;

  wSecond: Word;

  wMilliseconds: Word;

end;



TDateTime = type Double;



//TFileTime 相当于一个 Int64, 一般要通过给 TSystemTime 或 TDateTime 赋值, 然后转换过去.

//在例子中我是通过下面过程转过去的:

StrToDateTime -> DateTimeToSystemTime -> SystemTimeToFileTime -> LocalFileTimeToFileTime


 
   

下面程序指定在 2009年2月18号下午1点10分5秒时运行三个线程(窗体同上, 我已找了个合适的时间测试成功).

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    procedure Button1Click(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  f: Integer;

  hWaitableTimer: THandle;



function MyThreadFun(p: Pointer): DWORD; stdcall;

var

  i,y: Integer;

begin

  Inc(f);

  y := 20 * f;



  if WaitForSingleObject(hWaitableTimer, INFINITE) = WAIT_OBJECT_0 then

  begin

    for i := 0 to 1000 do

    begin

      Form1.Canvas.Lock;

      Form1.Canvas.TextOut(20, y, IntToStr(i));

      Form1.Canvas.Unlock;

      Sleep(1);

    end;

  end;

  Result := 0;

end;



procedure TForm1.Button1Click(Sender: TObject);

const

  strTime = '2009-2-18 13:10:5';

var

  ThreadID: DWORD;

  DueTime: Int64;

  st: TSystemTime;

  ft,UTC: TFileTime;

  dt: TDateTime;

begin

  DateTimeToSystemTime(StrToDateTime(strTime), st); {从 TDateTime 到 TSystemTime}

  SystemTimeToFileTime(st, ft);                     {从 TSystemTime 到 TFileTime}

  LocalFileTimeToFileTime(ft, UTC);                 {从本地时间到国际标准时间 UTC}

  DueTime := Int64(UTC);                            {函数需要的是 Int64}



  hWaitableTimer := CreateWaitableTimer(nil, True, nil);

  SetWaitableTimer(hWaitableTimer, DueTime, 0, nil, nil, False);



  Repaint; f := 0;

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

  CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID);

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  CloseHandle(hWaitableTimer);

end;



end.


 
   

接下来该是 WaitableTimer 对象的回调函数了.

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