[Delphi]多线程编程(8)多线程同步之CriticalSection(临.doc

先看一段程序, 代码文件: unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;type TForm1 = class(TForm) ListBox1: TListBox; Button1: TButton; procedure FormCreate(Sender: TObject); procedure Button1Click(Sender: TObject); end;var Form1: TForm1;implementation$R *.dfmfunction MyThreadFun(p: Pointer): DWORD; stdcall;var i: Integer;begin for i := 0 to 99 do Form1.ListBox1.Items.Add(IntToStr(i); Result := 0;end;procedure TForm1.Button1Click(Sender: TObject);var ID: DWORD;begin CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, nil, 0, ID);end;procedure TForm1.FormCreate(Sender: TObject);begin ListBox1.Align := alLeft;end;end.窗体文件: object Form1: TForm1 Left = 0 Top = 0 Caption = Form1 ClientHeight = 154 ClientWidth = 214 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = Tahoma Font.Style = OldCreateOrder = False OnCreate = FormCreate PixelsPerInch = 96 TextHeight = 13 object ListBox1: TListBox Left = 9 Top = 9 Width = 121 Height = 97 ItemHeight = 13 TabOrder = 0 end object Button1: TButton Left = 131 Top = 112 Width = 75 Height = 25 Caption = Button1 TabOrder = 1 OnClick = Button1Click endend在这段程序中, 有三个线程几乎是同时建立, 向窗体中的 ListBox1 中写数据, 最后写出的结果是这样的:能不能让它们别打架, 一个完了另一个再来? 这就要用到多线程的同步技术.前面说过, 最简单的同步手段就是 临界区.先说这个 同步(Synchronize), 首先这个名字起的不好, 我们好像需要的是 异步; 其实异步也不准确.管它叫什么名字呢, 它的目的就是保证不冲突、有次序、都发生.临界区(CriticalSection): 当把一段代码放入一个临界区, 线程执行到临界区时就独占了, 让其他也要执行此代码的线程先等等; 这和前面用的 Lock 和 UnLock 差不多; 使用格式如下:var CS: TRTLCriticalSection; 声明一个 TRTLCriticalSection 结构类型变量; 它应该是全局的InitializeCriticalSection(CS); 初始化EnterCriticalSection(CS); 开始: 轮到我了其他线程走开LeaveCriticalSection(CS); 结束: 其他线程可以来了DeleteCriticalSection(CS); 删除: 注意不能过早删除/也可用 TryEnterCriticalSection 替代 EnterCriticalSection.用上临界区, 重写上面的代码, 运行效果图:代码文件: unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;type TForm1 = class(TForm) ListBox1: TListBox; Button1: TButton; procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); procedure Button1Click(Sender: TObject); end;var Form1: TForm1;implementation$R *.dfmvar CS: TRTLCriticalSection;function MyThreadFun(p: Pointer): DWORD; stdcall;var i: Integer;begin EnterCriticalSection(CS); for i := 0 to 99 do Form1.ListBox1.Items.Add(IntToStr(i); LeaveCriticalSection(CS); Result := 0;end;procedure TForm1.Button1Click(Sender: TObject);var ID: DWORD;begin CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, nil, 0, ID);end;procedure TForm1.FormCreate(Sender: TObject);begin ListBox1.Align := alLeft; InitializeCriticalSection(CS);end;procedure TForm1.FormDestroy(Sender: TObject);begin DeleteCriticalSection(CS);end;end.Delphi 在 SyncObjs 单元给封装了一个 TCriticalSection 类, 用法差不多, 代码如下: unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;type TForm1 = class(TForm) ListBox1: TListBox; Button1: TButton; procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); procedure Button1Click(Sender: TObject); end;var Form1: TForm1;implementation$R *.dfmuses SyncObjs;var CS: TCriticalSection;function MyThreadFun(p: Pointer): DWORD; stdcall;var i: Integer;begin CS.Enter; for i := 0 to 99 do Form1.ListBox1.Items.Add(IntToStr(i); CS.Leave; Result := 0;end;procedure TForm1.Button1Click(Sender: TObject);var ID: DWORD;begin CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, nil, 0, ID); CreateThread(nil, 0, MyThreadFun, ni