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 程式師世界 >> 編程語言 >> 更多編程語言 >> Delphi >> 多線程編程(8)-多線程同步之CriticalSection(臨界區)

多線程編程(8)-多線程同步之CriticalSection(臨界區)

編輯:Delphi

先看一段程序, 代碼文件: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.

窗體文件: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

在這段程序中, 有三個線程幾乎是同時建立, 向窗體中的 ListBox1 中寫數據, 最後寫出的結果是這樣的:

多線程編程(8)-多線程同步之CriticalSection(臨界區)

能不能讓它們別打架, 一個完了另一個再來? 這就要用到多線程的同步技術.

前面說過, 最簡單的同步手段就是 "臨界區".

先說這個 "同步"(Synchronize), 首先這個名字起的不好, 我們好像需要的是 "異步"; 其實異步也不准確...

管它叫什麼名字呢, 它的目的就是保證不沖突、有次序、都發生.

"臨界區"(CriticalSection): 當把一段代碼放入一個臨界區, 線程執行到臨界區時就獨占了, 讓其他也要執行此代碼的線程先等等; 這和前面用的 Lock 和 UnLock 差不多; 使用格式如下:

var CS: TRTLCriticalSection;  {聲明一個 TRTLCriticalSection 結構類型變量; 它應該是全局的}
InitializeCriticalSection(CS); {初始化}
EnterCriticalSection(CS);   {開始: 輪到我了其他線程走開}
LeaveCriticalSection(CS);   {結束: 其他線程可以來了}
DeleteCriticalSection(CS);   {刪除: 注意不能過早刪除}
//也可用 TryEnterCriticalSection 替代 EnterCriticalSection.

用上臨界區, 重寫上面的代碼, 運行效果圖:

多線程編程(8)-多線程同步之CriticalSection(臨界區)

代碼文件: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 單元給封裝了一個 TCriticalSection 類, 用法差不多, 代碼如下: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.

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