多线程编程(3)--从CreateThread说起（倒数第二个参数）

转载自：万一的博客

function CreateThread(
  lpThreadAttributes: Pointer;
  dwStackSize: DWORD;
  lpStartAddress: TFNThreadStartRoutine;
  lpParameter: Pointer;
  dwCreationFlags: DWORD; {启动选项}
  var lpThreadId: DWORD
): THandle; stdcall;

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

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

　　什么是挂起计数？

　　SuspendThread会个这个数+1， ResumeThread会给这个数-1；但是这个数最小是0。如果这个数是0，线程会运行； >0 时会挂起。所以如果被SuspendThread 多次，同样需要ResumeThread 多次才能恢复线程的运行

　　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 和SuspendThread这两个函数，运行效果图如下

　　代码如下

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
    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.

　　下面是窗体文件

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

　　接下来应该是 CreateThread的第四个参数了（也就是倒数第三个参数）