[NumLock]

На форме 5 меток и кнопка. При нажатии на кнопку стартует поток с незанятой меткой. После завершения потока метка снова освобождается.

Код:

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TMyThread = class(TThread)
  protected
    procedure Execute; override;
  public
    FLabel: TLabel;
    constructor Create(ALabel: TLabel); overload;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    Label5: TLabel;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    procedure ThreadTerminate(Sender: TObject);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TMyThread }

constructor TMyThread.Create(ALabel: TLabel);
begin
  FLabel:=ALabel;
  FreeOnTerminate:=True;
  inherited Create(False);
end;

procedure TMyThread.Execute;
var
  TickCount: Integer;
begin
  TickCount:=Random(10)+1;

  Synchronize(procedure
    begin
      FLabel.Caption:=IntToStr(TickCount);
    end);

  (* do it *)
  while TickCount>0 do
  begin
    Synchronize(procedure
      begin
        FLabel.Caption:=IntToStr(TickCount);
      end);
    Dec(TickCount);
    Sleep(1000);
  end;

  Synchronize(procedure
    begin
      FLabel.Tag:=0;
      FLabel.Caption:='stoped';
    end);
end;

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  Randomize;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i: Integer;
  lbl: TLabel;
  rslt: Boolean;
begin
  rslt:=False;
  for i:=1 to 5 do
  begin
    lbl:=TLabel(FindComponent('Label'+IntToStr(i)));
    if lbl.Tag=0 then
    begin
      lbl.Tag:=$7FFFFFFF;
      Button1.Tag:=Button1.Tag+1;
      Button1.Caption:=IntToStr(Button1.Tag);
      with TMyThread.Create(lbl) do OnTerminate:=ThreadTerminate;
      rslt:=True;
      Break;
    end;
  end;
  if not rslt then ShowMessage('Oops');
end;

procedure TForm1.ThreadTerminate(Sender: TObject);
begin
  Button1.Tag:=Button1.Tag-1;
  Button1.Caption:=IntToStr(Button1.Tag);
end;

end.