多線程編程(3) – 多線程同步之 CriticalSection(臨界區)

"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佔了, 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 結構類型變數; 它應該是全域的}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.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;
Delphi 在 SyncObjs 單元給封裝了一個 TCriticalSection 類, 用法差不多
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;