InnoSetup timer block all page - inno-setup-v6

Question

I need to get the output of the execution of my script and integrate it into the installer, everything works well, but I need to add a "cancel" button, it will not be difficult to add a button, but during the execution of the timer, the entire installer window is blocked, but I can not minimize to tray and press any button.
function SetTimer(
Wnd: LongWord; IDEvent, Elapse: LongWord; TimerFunc: LongWord): LongWord;
external 'SetTimer#user32.dll stdcall';
function KillTimer(hWnd: LongWord; uIDEvent: LongWord): BOOL;
external 'KillTimer#user32.dll stdcall';
var
ProgressFileName: string;
function BufferToAnsi(const Buffer: string): AnsiString;
var
W: Word;
I: Integer;
begin
SetLength(Result, Length(Buffer) * 2);
for I := 1 to Length(Buffer) do
begin
W := Ord(Buffer[I]);
Result[(I * 2)] := Chr(W shr 8); { high byte }
Result[(I * 2) - 1] := Chr(Byte(W)); { low byte }
end;
end;
procedure UpdateProgress;
var
S: AnsiString;
I, L, Max: Integer;
Buffer: string;
Stream: TFileStream;
Lines: TStringList;
begin
if not FileExists(ProgressFileName) then
begin
Log(Format('Progress file %s does not exist', [ProgressFileName]));
end
else
begin
try
Stream := TFileStream.Create(ProgressFileName, fmOpenRead or fmShareDenyNone);
try
L := Stream.Size;
Max := 100*2014;
if L > Max then
begin
Stream.Position := L - Max;
L := Max;
end;
SetLength(Buffer, (L div 2) + (L mod 2));
Stream.ReadBuffer(Buffer, L);
S := BufferToAnsi(Buffer);
finally
Stream.Free;
end;
except
Log(Format('Failed to read progress from file %s - %s', [
ProgressFileName, GetExceptionMessage]));
end;
end;
if S <> '' then
begin
Log('Progress len = ' + IntToStr(Length(S)));
Lines := TStringList.Create();
Lines.Text := S;
for I := 0 to Lines.Count - 1 do
begin
if I < ProgressListBox.Items.Count then
begin
ProgressListBox.Items[I] := Lines[I];
end
else
begin
ProgressListBox.Items.Add(Lines[I]);
end
end;
ProgressListBox.ItemIndex := ProgressListBox.Items.Count - 1;
ProgressListBox.Selected[ProgressListBox.ItemIndex] := False;
Lines.Free;
end;
ProgressPage.SetProgress(0, 1);
end;
procedure UpdateProgressProc(
H: LongWord; Msg: LongWord; Event: LongWord; Time: LongWord);
begin
UpdateProgress;
end;
procedure RunInstallBatInsideProgress;
var
ResultCode: Integer;
Timer: LongWord;
AppPath: string;
AppError: string;
Command: string;
begin
ProgressPage :=
CreateOutputProgressPage(
'Installing something', 'Please wait until this finishes...');
ProgressPage.Show();
ProgressListBox := TNewListBox.Create(WizardForm);
ProgressListBox.Parent := ProgressPage.Surface;
ProgressListBox.Top := 0;
ProgressListBox.Left := 0;
ProgressListBox.Width := ProgressPage.SurfaceWidth;
ProgressListBox.Height := ProgressPage.SurfaceHeight;
ProgressPage.ProgressBar.Top := -100;
try
Timer := SetTimer(0, 0, 250, CreateCallback(#UpdateProgressProc));
AppPath := ExpandConstant('{app}\installer.py');
ProgressFileName := ExpandConstant('{app}\tmp\installer-progress.log');
Log(Format('Expecting progress in %s', [ProgressFileName]));
Command := Format('""%s" > "%s""', [AppPath, ProgressFileName]);
if not Exec(ExpandConstant('{cmd}'), '/c ' + Command + ExpandConstant(' {app}\PIPE'), '', SW_HIDE, ewWaitUntilTerminated, ResultCode) then
begin
AppError := 'Cannot start app';
end
else
if ResultCode <> 0 then
begin
AppError := Format('App failed with code %d', [ResultCode]);
end;
UpdateProgress;
finally
KillTimer(0, Timer);
ProgressPage.Hide;
DeleteFile(ProgressFileName);
ProgressPage.Free();
end;
if AppError <> '' then
begin
RaiseException(AppError);
end;
end;
procedure CurStepChanged(CurStep: TSetupStep);
begin
if CurStep=ssPostInstall then
begin
RunInstallBatInsideProgress;
end
end;
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