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