Good change in general, but why don't you simply start the timer at the place where showProgress() was emitted before, in case it's not running yet? Then you wouldn't need the "toggled on/off" state for the timer.

You mean make the timer single shot and change to this in updateProgress?

if (!m_progressTimer.isActive()) {
    m_progressTimer.start();
}

Yes, that sounds good to me.

In D3110#65004, @brauch wrote:

Since this patch, I frequently see the background parser idle but the progress bar displaying "0%" like it's doing something. Did anybody else see this?

I'm see this annoying progress bar too. Should be fixed.

Maybe we need to move this check

//We don't hide the progress-bar in updateProgressBar, so it doesn't permanently flash when a document is reparsed again and again.
if(m_doneParseJobs == m_maxParseJobs
    || (m_neededPriority == BackgroundParser::BestPriority && m_weaver.queueLength() == 0))
{
    emit m_parser->hideProgress(m_parser);
}

to updateProgressBar().

Can you try this out and push it if it fixes the issue? Thanks :)

Submitted D3537.