Limit DRI2Drawable reference leak

[Ville Syrjälä]

On Sat, Feb 21, 2015 at 10:52:49PM +0000, Chris Wilson wrote:
> On Sun, Feb 22, 2015 at 12:13:38AM +0200, Ville Syrjälä wrote:
> > On Sat, Feb 21, 2015 at 09:31:07PM +0000, Chris Wilson wrote:
> > > With the current protocol and implementations, we have to often call
> > > DRI2CreateDrawable but can never call DRI2DestroyDrawable. This ends up
> > > with us leaking references to DRI2Drawables based on the assumption that
> > > the references have identical lifetimes to the Drawable going astray.
> > > This was spotted by Daniel Drake as the mali driver would create a new
> > > reference to the DRI2Drawable on every GetBuffers, but it can also be
> > > observed in mesa when running synthetic benchmarks (creating lots of
> > > contexts/glxdrawables for each window) and to a lesser extent with
> > > normal composited operation.
> > > 
> > > The first two patches implement the capping of the unnamed internal
> > > reference used by DRI2CreateDrawable to just one per Client.
> > 
> > IIRC we had many issues around the dri2 reference stuff during the
> > Maemo days. Pauli fixed tons of problems in the dri2 code but some
> > of the patches never made it in.
> > 
> > These seem somewhat relevant:
> > http://lists.x.org/archives/xorg-devel/2010-November/014783.html
> > http://lists.x.org/archives/xorg-devel/2010-November/014782.html
> 
> Indeed. Same problem, similar solution. I was a bit dubious as to
> whether we could hook up DRI2DestroyDrawable after all this time (for
> example mesa ignores it except for GLXPixmaps) and feared there was some
> corner case that was going to explode.

Yeah dunno. This code did ship in the N9/N950 and our client side did
issue these protocol requests appropriately. But then again, Pauli did
a boatload of additional work on the dri2 code after these that didn't
make it into upstream either.

As I recall one of the issues was clients getting BadDrawables from
DRI2DestroyDrawable if the X drawable already went away. And the
solution was to decouple the lifetimes of the two.

I've probably forgotten most of what we did back then, but interested
parties may go dig through
https://www.gitorious.org/meego-w40/xserver-xorg if they wish.

-- 
Ville Syrjälä
syrjala at sci.fi
http://www.sci.fi/~syrjala/