多线程编程(9) - 认识等待函数 WaitForSingleObject

一下子跳到等待函数 WaitForSingleObject, 是因为下面的 Mutex、Semaphore、Event、WaitableTimer 等同步手段都要使用这个函数; 不过等待函数可不止 WaitForSingleObject 它一个, 但它最简单.

function WaitForSingleObject(

  hHandle: THandle;      {要等待的对象句柄}

  dwMilliseconds: DWORD  {等待的时间, 单位是毫秒}

): DWORD; stdcall;       {返回值如下:}



WAIT_OBJECT_0  {等着了, 本例中是: 等的那个进程终于结束了}

WAIT_TIMEOUT   {等过了点(你指定的时间), 也没等着}

WAIT_ABANDONED {好不容易等着了, 但人家还是不让咱执行; 这一般是互斥对象}



//WaitForSingleObject 的第二个参数一般给常数值 INFINITE, 表示一直等下去, 死等.


 
   

WaitForSingleObject 等待什么? 在多线程里就是等待另一个线程的结束, 快来执行自己的代码; 不过它可以等待的对象可不止线程; 这里先来一个等待另一个进程结束的例子, 运行效果图:

---

代码文件:

---

unit Unit1;



interface



uses

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

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    procedure Button1Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  hProcess: THandle; {进程句柄}



{等待一个指定句柄的进程什么时候结束}

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

begin

  if WaitForSingleObject(hProcess, INFINITE) = WAIT_OBJECT_0 then

    Form1.Text := Format('进程 %d 已关闭', [hProcess]);

  Result := 0;

end;



{启动一个进程, 并建立新线程等待它的结束}

procedure TForm1.Button1Click(Sender: TObject);

var

  pInfo: TProcessInformation;

  sInfo: TStartupInfo;

  Path: array[0..MAX_PATH-1] of Char;

  ThreadID: DWORD;

begin

  {先获取记事本的路径}

  GetSystemDirectory(Path, MAX_PATH);

  StrCat(Path, '\notepad.exe');



  {用 CreateProcess 打开记事本并获取其进程句柄, 然后建立线程监视}

  FillChar(sInfo, SizeOf(sInfo), 0);

  if CreateProcess(Path, nil, nil, nil, False, 0, nil, nil, sInfo, pInfo) then

  begin

    hProcess := pInfo.hProcess;                           {获取进程句柄}

    Text := Format('进程 %d 已启动', [hProcess]); 

    CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); {建立线程监视}

  end;

end;



end.


 
   

窗体文件:

---

object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 124

  ClientWidth = 241

  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 = 88

    Top = 56

    Width = 75

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

end