unit Main;

interface

uses

 Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,

 StdCtrls;

type

 TMainForm = class(TForm)

  Button1: TButton;

  procedure Button1Click(Sender: TObject);

 private

  { Private declarations }

 public

  { Public declarations }

 end;

var

 MainForm: TMainForm;

implementation

{$R *.DFM}

{ NOTE: Change GlobalStr from var to threadvar to see difference }

var

 //threadvar

 GlobalStr: string;

type

 TTLSThread = class(TThread)

 private

  FNewStr: string;

 protected

  procedure Execute; override;

 public

  constructor Create(const ANewStr: string);

 end;

procedure SetShowStr(const S: string);

begin

 if S = '' then

  MessageBox(0, PChar(GlobalStr), 'The string is...', MB_OK)

 else

  GlobalStr := S;

end;

constructor TTLSThread.Create(const ANewStr: string);

begin

 FNewStr := ANewStr;

 inherited Create(False);

end;

procedure TTLSThread.Execute;

begin

 FreeOnTerminate := True;

 SetShowStr(FNewStr);

 SetShowStr('');

end;

procedure TMainForm.Button1Click(Sender: TObject);

begin

 SetShowStr('Hello world');

 SetShowStr('');

 TTLSThread.Create('Dilbert');

 Sleep(100);

 SetShowStr('');

end;

end.