用訊號燈的方式，限制thread同時執行的數目

MainForm

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    FSemaphor: THandle;
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
uses Unit2;
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
  FSemaphor := CreateSemaphore( nil, 3, 3, nil );
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
  CloseHandle( FSemaphor );
end;
procedure TForm1.Button1Click(Sender: TObject);
var
  aIndex: Integer;
  aExchange: TExchange;
begin
  for aIndex := 1 to 20 do
  begin
    if ( WaitForSingleObject( FSemaphor, INFINITE ) = WAIT_OBJECT_0 ) then
    begin
      aExchange := TExchange.Create( True, FSemaphor );
      aExchange.FreeOnTerminate := True;
      aExchange.Resume;
    end;
  end;
end;
end.

Thread

type
  TExchange = class(TThread)
  private
    { Private declarations }
    FSemaphor: THandle;
  protected
    procedure Execute; override;
  public
    constructor Create(CreateSuspended:Boolean; ASemaphor: THandle); reintroduce;
  end;
implementation
{ TExchange }
constructor TExchange.Create(CreateSuspended: Boolean; ASemaphor: THandle);
begin
  inherited Create( CreateSuspended );
  FSemaphor := ASemaphor;
end;
procedure TExchange.Execute;
begin
  while not Self.Terminated do
  begin
    Sleep( 10000 );
    Break;
  end;
  ReleaseSemaphore( FSemaphor, 1, nil );
end;