多线程编程(3) - 从 CreateThread 说起[续]

function CreateThread(

  lpThreadAttributes: Pointer;

  dwStackSize: DWORD;

  lpStartAddress: TFNThreadStartRoutine;

  lpParameter: Pointer;

  dwCreationFlags: DWORD; {启动选项}

  var lpThreadId: DWORD

): THandle; stdcall;


 
   

CreateThread 的倒数第二个参数 dwCreationFlags(启动选项) 有两个可选值:
0: 线程建立后立即执行入口函数;
CREATE_SUSPENDED: 线程建立后会挂起等待.

可用 ResumeThread 函数是恢复线程的运行; 可用 SuspendThread 再次挂起线程.
这两个函数的参数都是线程句柄, 返回值是执行前的挂起计数.

什么是挂起计数?
SuspendThread 会给这个数 +1; ResumeThread 会给这个数 -1; 但这个数最小是 0.
当这个数 = 0 时, 线程会运行; > 0 时会挂起.
如果被 SuspendThread 多次, 同样需要 ResumeThread 多次才能恢复线程的运行.

在下面的例子中, 有新线程不断给一个全局变量赋随机值;
同时窗体上的 Timer 控件每隔 1/10 秒就把这个变量写在窗体标题;
在这个过程中演示了 ResumeThread、SuspendThread 两个函数.

运行效果图:

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代码文件:

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unit Unit1;



interface



uses

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

  Dialogs, StdCtrls, ExtCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    Timer1: TTimer;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

    procedure FormCreate(Sender: TObject);

    procedure Timer1Timer(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  hThread: THandle; {线程句柄}

  num: Integer;     {全局变量, 用于记录随机数}



{线程入口函数}

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

begin

  while True do {假如线程不挂起, 这个循环将一直循环下去}

  begin

    num := Random(100);

  end;

  Result := 0;

end;



{建立并挂起线程}

procedure TForm1.Button1Click(Sender: TObject);

var

  ID: DWORD;

begin

  hThread := CreateThread(nil, 0, @MyThreadFun, nil, CREATE_SUSPENDED, ID);

  Button1.Enabled := False;

end;



{唤醒并继续线程}

procedure TForm1.Button2Click(Sender: TObject);

begin

  ResumeThread(hThread);

end;



{挂起线程}

procedure TForm1.Button3Click(Sender: TObject);

begin

  SuspendThread(hThread);

end;



{下面是窗体代码}

procedure TForm1.FormCreate(Sender: TObject);

begin

  Timer1.Interval := 100;

end;



procedure TForm1.Timer1Timer(Sender: TObject);

begin

  Text := IntToStr(num);

end;



end.


 
   

窗体文件:

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object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 86

  ClientWidth = 269

  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 = 16

    Top = 24

    Width = 75

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

  object Button2: TButton

    Left = 97

    Top = 24

    Width = 75

    Height = 25

    Caption = 'Button2'

    TabOrder = 1

    OnClick = Button2Click

  end

  object Button3: TButton

    Left = 178

    Top = 24

    Width = 75

    Height = 25

    Caption = 'Button3'

    TabOrder = 2

    OnClick = Button3Click

  end

  object Timer1: TTimer

    OnTimer = Timer1Timer

  end

end


 
   

ResumeThread 和 SuspendThread 分别对应 TThread 的 Resume 和 Suspend 方法, 很好理解.

接下来应该是 CreateThread 的第四个参数了.

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