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.