多线程编程(3) 多线程同步之 CriticalSection(临界区)

"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.
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 单元给封装了一个 TCriticalSection 类, 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;