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:

---

代码文件:

---

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:

---

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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