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 程式師世界 >> 編程語言 >> 更多編程語言 >> Delphi >> 多線程編程(15) - 多線程同步之 WaitableTimer (等待定時器對象)[續]

多線程編程(15) - 多線程同步之 WaitableTimer (等待定時器對象)[續]

編輯:Delphi

本次專門研究下 SetWaitableTimer 的第二個參數(起始時間).

  它有正值、負值、0值三種情況, 前面已用過 0值.

  先學習負值(相對時間), 也就是從當前算起隔多長時間開始執行.

  這個相對時間是已 1/100 納秒為單位的, 譬如賦值 3*10000000 相當於 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(納秒);
1 s(秒) = 1,000,000,000,000 ps(皮秒);

  本例效果圖:

  多線程編程(15) - 多線程同步之 WaitableTimer (等待定時器對象)[續]

  代碼文件:

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秒鐘後執行}
 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.

窗體文件:

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

  當我們需要一個絕對時間時, 譬如 2009-2-18 13:10:5, 函數需要的 Int64 值應該是個 TFileTime 格式的時間.

  先看三種相關時間類型(TFileTime、TSystemTime、TDateTime)的定義:

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 相當於一個 Int64, 一般要通過給 TSystemTime 或 TDateTime 賦值, 然後轉換過去.
//在例子中我是通過下面過程轉過去的:
StrToDateTime -> DateTimeToSystemTime -> SystemTimeToFileTime -> LocalFileTimeToFileTime

下面程序指定在 2009年2月18號下午1點10分5秒時運行三個線程(窗體同上, 我已找了個合適的時間測試成功).

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); {從 TDateTime 到 TSystemTime}
 SystemTimeToFileTime(st, ft);           {從 TSystemTime 到 TFileTime}
 LocalFileTimeToFileTime(ft, UTC);         {從本地時間到國際標准時間 UTC}
 DueTime := Int64(UTC);              {函數需要的是 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.

 接下來該是 WaitableTimer 對象的回調函數了.


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