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