unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    ProgressBar1: TProgressBar;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    Thread: TThread;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  Thread.Resume;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Thread.Suspend;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.Caption := 'start';
  Button2.Caption := 'stop';
  ProgressBar1.Max := 1000;

  Thread := TThread.CreateAnonymousThread(
    procedure
    begin
      while ProgressBar1.Position < ProgressBar1.Max do
      begin
        ProgressBar1.Position := ProgressBar1.Position + 1;

        Form1.Caption := ProgressBar1.Position.ToString;
      end;
    end);
end;

end.

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Thread.Suspend;
  Thread.Terminate;
end;