多线程编程(13) - 多线程同步之 Event (事件对象)

据说 Event(事件对象) 是多线程最原始的同步手段, 我觉得它是最灵活的一个.
Event 对象(的句柄表)中主要有两个布尔变量, 从它的建立函数中可以看得清楚:

function CreateEvent(

  lpEventAttributes: PSecurityAttributes; {安全设置}

  bManualReset: BOOL;                     {第一个布尔}

  bInitialState: BOOL;                    {第二个布尔}

  lpName: PWideChar                       {对象名称}

): THandle; stdcall;                      {返回对象句柄}



//第一个布尔为 False 时, 事件对象控制一次后将立即重置(暂停); 为 True 时可手动暂停.

//第二个布尔为 False 时, 对象建立后控制为暂停状态; True 是可运行状态.


 
   

和其他同类相比, 它的灵活性在于可随时 "启动运行"(SetEvent) 和 "暂停运行"(ResetEvent);
甚至还有个 PulseEvent 函数, 能控制执行一次后立即暂停, 很是方便.

---

本例效果图:

---

代码文件:

---

unit Unit1;



interface



uses

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

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    Button4: TButton;

    Button5: TButton;

    procedure FormCreate(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

    procedure Button4Click(Sender: TObject);

    procedure Button5Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  f: Integer;      {用这个变量协调一下各线程输出的位置}

  hEvent: THandle; {事件对象的句柄}



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

var

  i,y: Integer;

begin

  Inc(f);

  y := 20 * f;

  for i := 0 to 200000 do

  begin

    if WaitForSingleObject(hEvent, INFINITE) = WAIT_OBJECT_0 then

    begin

      Form1.Canvas.Lock;

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

      Form1.Canvas.Unlock;

    end;

  end;

  Result := 0;

end;



procedure TForm1.Button1Click(Sender: TObject);

begin

  Repaint; f := 0;

  CloseHandle(hEvent); {如果已经创建过}

  hEvent := CreateEvent(nil, True, True, nil);

end;



{创建线程}

procedure TForm1.Button2Click(Sender: TObject);

var

  ThreadID: DWORD;

begin

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

end;



{暂停}

procedure TForm1.Button3Click(Sender: TObject);

begin

  ResetEvent(hEvent);

end;



{启动}

procedure TForm1.Button4Click(Sender: TObject);

begin

  SetEvent(hEvent);

end;



{启动后执行一次立即暂停}

procedure TForm1.Button5Click(Sender: TObject);

begin

  PulseEvent(hEvent);

end;



procedure TForm1.FormCreate(Sender: TObject);

begin

  Button1.Caption := '创建 Event 对象';

  Button2.Caption := '创建线程';

  Button3.Caption := 'ResetEvent';

  Button4.Caption := 'SetEvent';

  Button5.Caption := 'PulseEvent';

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  CloseHandle(hEvent);

end;



end.


 
   

窗体文件:

---

object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 149

  ClientWidth = 228

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  OnCreate = FormCreate

  PixelsPerInch = 96

  TextHeight = 13

  object Button1: TButton

    Left = 8

    Top = 116

    Width = 129

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

  object Button3: TButton

    Left = 143

    Top = 12

    Width = 75

    Height = 25

    Caption = 'Button3'

    TabOrder = 1

    OnClick = Button3Click

  end

  object Button4: TButton

    Left = 143

    Top = 43

    Width = 75

    Height = 25

    Caption = 'Button4'

    TabOrder = 2

    OnClick = Button4Click

  end

  object Button5: TButton

    Left = 143

    Top = 74

    Width = 75

    Height = 25

    Caption = 'Button5'

    TabOrder = 3

    OnClick = Button5Click

  end

  object Button2: TButton

    Left = 143

    Top = 116

    Width = 75

    Height = 25

    Caption = 'Button2'

    TabOrder = 4

    OnClick = Button2Click

  end

end


 
   

和前面一样, 再用 SyncObjs 单元下的 TEvent 类实现一次; 不过它没有实现类似 PulseEvent 的功能:

---

unit Unit1;



interface



uses

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

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    Button4: TButton;

    Button5: TButton;

    procedure FormCreate(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

    procedure Button4Click(Sender: TObject);

    procedure Button5Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



uses SyncObjs;

var

  f: Integer;

  MyEvent: TEvent;



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

var

  i,y: Integer;

begin

  Inc(f);

  y := 20 * f;

  for i := 0 to 200000 do

  begin

    if MyEvent.WaitFor(INFINITE) = wrSignaled then

    begin

      Form1.Canvas.Lock;

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

      Form1.Canvas.Unlock;

    end;

  end;

  Result := 0;

end;



procedure TForm1.Button1Click(Sender: TObject);

begin

  Repaint; f := 0;

  if Assigned(MyEvent) then MyEvent.Free;

  MyEvent := TEvent.Create(nil, True, True, '');

end;



{创建线程}

procedure TForm1.Button2Click(Sender: TObject);

var

  ThreadID: DWORD;

begin

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

end;



{暂停}

procedure TForm1.Button3Click(Sender: TObject);

begin

  MyEvent.ResetEvent;

end;



{启动}

procedure TForm1.Button4Click(Sender: TObject);

begin

  MyEvent.SetEvent;

end;



{启动后执行一次立即暂停}

procedure TForm1.Button5Click(Sender: TObject);

begin

  ShowMessage('TEvent 类没有提供这个功能'); {我试过用 PulseEvent(MyEvent.Handle) 也不行}

end;



procedure TForm1.FormCreate(Sender: TObject);

begin

  Button1.Caption := '创建 Event 对象';

  Button2.Caption := '创建线程';

  Button3.Caption := 'ResetEvent';

  Button4.Caption := 'SetEvent';

  Button5.Caption := 'PulseEvent';

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  MyEvent.Free;

end;



end.