Re: [Audacity-devel] TrackArtist::UpdatePrefs() race

[Leland <le...@au...>]

Martyn Shaw wrote:
> Hi
> 
> I see problem with TrackArtist::UpdatePrefs() not being called soon 
> enough when I close the prefs dialog after changing the Spectrogram size.
> 
> Calls from TrackArtist::DrawClipSpectrum to clip->GetSpectrogram rely 
> on TrackArtist::UpdatePrefs() having updated mWindowSize, which it 
> hasn't yet done.  clip->GetSpectrogram reads the pref directly so has 
> the 'current' size.  Mismatch of sizes causes a crash if you are 
> increasing the windowSize and an incorrect drawing if you aren't.
> 
> Obviously I could fix this specific case, but there may be others, so 
> I looked further.
> 
> 'OK' on the AudacityProject::OnPreferences() dialog causes an onPaint 
> event which does the drawing of the spectrogram, 
> AudacityProject::UpdatePrefs() (which calls 
> TrackArtist::UpdatePrefs()) comes after that.  Should we be calling 
> AudacityProject::OnPreferences() from PrefsDialog::OnOK?  Maybe that 
> would be safer?
> 
Safer, yes, and corrected.

But, what I'd really go for is a "registration and update notification"
kind of system where classes that need to know when specific (or 
wildcarded) keys get updated, they simply register a function callback 
with a Preferences class.  When the value for the indicated key gets 
updated, the registered function is called.

In a way, we've already done this...sort of.  That's what all of the 
UpdatePrefs() functions are for.  Unfortunately, it's a really manual 
sort of process right now.

Leland