How to cancel a synchronous IO operation? - multithreading

Question

I wrote this code to test how async IO cancellation works... But the read operation it's not canceled... When I call CancelSynchronousIo, the execution is blocked until thread finishes and then I get Element not found error. Do you have any idea what I did wrong ?
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;
end;
TForm1 = class(TForm)
BStartRead: TButton;
Memo1: TMemo;
BCancel: TButton;
procedure BStartReadClick(Sender: TObject);
procedure BCancelClick(Sender: TObject);
private
T1: TMyThread;
procedure LogMsg(var Msg: TMessage); message WM_USER;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TMyThread.Execute;
var Buff: TBytes;
hFile: THandle;
StrMsg, FileName: String;
N: Cardinal;
begin
SetLength(Buff, 200000000);
FileName:= '...some file...';
hFile:= CreateFile(PChar('\\?\'+FileName), GENERIC_READ, FILE_SHARE_READ, nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
if hFile <> INVALID_HANDLE_VALUE then begin
StrMsg:= 'Start reading...'; SendMessage(Form1.Handle, WM_USER, WPARAM(#StrMsg), 0);
if ReadFile(hFile, Buff[0], 200000000, N, nil)
then StrMsg:= 'Successfuly terminated.'
else StrMsg:= 'Error: canceled !';
SendMessage(Form1.Handle, WM_USER, WPARAM(#StrMsg), 0);
CloseHandle(hFile);
end
else begin
StrMsg:= 'Error: failed to open file !';
SendMessage(Form1.Handle, WM_USER, WPARAM(#StrMsg), 0);
end;
end;
//---- VCL -----
procedure TForm1.BStartReadClick(Sender: TObject);
begin
T1:= TMyThread.Create;
end;
procedure TForm1.BCancelClick(Sender: TObject);
begin
if CancelSynchronousIo(T1.Handle) then Memo1.Lines.Add('Cancel result: success')
else Memo1.Lines.Add('Cancel result: '+SysErrorMessage(GetLastError));
end;
procedure TForm1.LogMsg(var Msg: TMessage);
begin
case Msg.Msg of
WM_USER: Memo1.Lines.Add(PString(Msg.WParam)^.Substring(0));
end;
end;
end.