多线程编程(17) - 多线程同步之 WaitableTimer (等待定时器对象)[续三]

根据 WaitableTimer 的主要功用, 现在再把它放在 "线程同步" 的话题中讨论有点不合适了, 就要结束它.

//重新看看那个 APC 回调函数的格式:
procedure TimerAPCProc(
  lpArgToCompletionRoutine: Pointer;
  dwTimerLowValue, dwTimerHighValue: DWORD
); stdcall;

TimerAPCProc 的后两个参数其实是在传递一个值, 使用时要把它们合并为一个 TFileTime 类型的时间.
这个时间是 APC 函数被调用的时间, 稍稍修改上面一个例子看一下:

---

代码文件:

---

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  hTimer: THandle;

{APC 函数}
procedure TimerAPCProc(lpArgToCompletionRoutine: Pointer; dwTimerLowValue: DWORD;
  dwTimerHighValue: DWORD); stdcall;
var
  UTCFileTime,LocalFileTime: TFileTime;
  SystemTime: TSystemTime;
  DateTime: TDateTime;
begin
  {把 dwTimerLowValue 与 dwTimerHighValue 和并为一个 TFileTime 格式的时间}
  UTCFileTime.dwLowDateTime := dwTimerLowValue;
  UTCFileTime.dwHighDateTime := dwTimerHighValue;

  FileTimeToLocalFileTime(UTCFileTime, LocalFileTime); {从世界标准计时到本地时间}
  FileTimeToSystemTime(LocalFileTime, SystemTime);     {转到系统格式时间}
  DateTime := SystemTimeToDateTime(SystemTime);        {再转到 TDateTime}

  Form1.Text := DateTimeToStr(DateTime);
  SleepEx(INFINITE, True);
end;

{线程入口函数}
function MyThreadFun(p: Pointer): Integer; stdcall;
var
  DueTime: Int64;
begin
  DueTime := 0;
  if SetWaitableTimer(hTimer, DueTime, 1000, @TimerAPCProc, nil, False) then
  begin
    SleepEx(INFINITE, True);
  end;
  Result := 0;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ID: DWORD;
begin
  if hTimer = 0 then  hTimer := CreateWaitableTimer(nil, True, nil);
  CreateThread(nil, 0, @MyThreadFun, nil, 0, ID);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  CancelWaitableTimer(hTimer);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  CloseHandle(hTimer);
end;

end.

窗体文件:

---

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 86
  ClientWidth = 256
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 23
    Top = 32
    Width = 97
    Height = 25
    Caption = #21551#21160#23450#26102#22120
    TabOrder = 0
    OnClick = Button1Click
  end
  object Button2: TButton
    Left = 134
    Top = 32
    Width = 97
    Height = 25
    Caption = #21462#28040#23450#26102#22120
    TabOrder = 1
    OnClick = Button2Click
  end
end

SetWaitableTimer 中回调函数后面的指针参数, 将被传递给 APC 函数的第一个参数;
作为指针它可以携带任何数据, 这里让它携带了一个坐标点(鼠标点击窗体的位置), 下例效果图:

---

代码文件:

---

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    procedure FormDestroy(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  hTimer: THandle;
  pt: TPoint;

{APC 函数}
procedure TimerAPCProc(lpArgToCompletionRoutine: Pointer; dwTimerLowValue: DWORD;
  dwTimerHighValue: DWORD); stdcall;
var
  UTCFileTime,LocalFileTime: TFileTime;
  SystemTime: TSystemTime;
  DateTime: TDateTime;
  pt2: TPoint;
begin
  UTCFileTime.dwLowDateTime := dwTimerLowValue;
  UTCFileTime.dwHighDateTime := dwTimerHighValue;

  FileTimeToLocalFileTime(UTCFileTime, LocalFileTime);
  FileTimeToSystemTime(LocalFileTime, SystemTime);
  DateTime := SystemTimeToDateTime(SystemTime);

  pt2 := PPoint(lpArgToCompletionRoutine)^; {接受指针参数}
  Form1.Canvas.Lock;
  Form1.Canvas.TextOut(pt2.X, pt2.Y, DateTimeToStr(DateTime));
  Form1.Canvas.Unlock;

  SleepEx(INFINITE, True);
end;

{线程入口函数}
function MyThreadFun(p: Pointer): Integer; stdcall;
var
  DueTime: Int64;
begin
  DueTime := 0;
  {参数 @pt 在这里是鼠标点击窗体时的坐标结构的指针, 它将传递给 APC 函数的第一个参数}
  if SetWaitableTimer(hTimer, DueTime, 1000, @TimerAPCProc, @pt, False) then
  begin
    SleepEx(INFINITE, True);
  end;
  Result := 0;
end;

{建立 WaitableTimer 对象和线程}
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  ID: DWORD;
begin
  pt := Point(X,Y); {在这里个全局的坐标点赋值}
  if hTimer = 0 then  hTimer := CreateWaitableTimer(nil, True, nil);
  CreateThread(nil, 0, @MyThreadFun, nil, 0, ID);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  CloseHandle(hTimer);
end;

end.

窗体文件:

---

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 135
  ClientWidth = 195
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  OnMouseDown = FormMouseDown
  PixelsPerInch = 96
  TextHeight = 13
end