先看一段程序, 代码文件:
unit Unit1; interface uses 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 *.dfm} function 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 end end
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:
![](https://www.cnblogs.com/images/cnblogs_com/del/174185/o_0921201.png)
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:
![](https://www.cnblogs.com/images/cnblogs_com/del/174185/o_0921202.gif)
代码文件:
unit Unit1; interface uses 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 *.dfm} var 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; interface uses 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 *.dfm} uses 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, nil, 0, ID); end; procedure TForm1.FormCreate(Sender: TObject); begin ListBox1.Align := alLeft; CS := TCriticalSection.Create; end; procedure TForm1.FormDestroy(Sender: TObject); begin CS.Free; end; end.