[cairo] fixing Cairo's FreeType multi-threaded usage
Behdad Esfahbod
behdad at behdad.org
Thu Apr 5 09:05:49 PDT 2007
On Thu, 2007-04-05 at 03:08 -0400, David Turner wrote:
> Hello everyone,
>
> I would *really* appreciate if you could review or even integrate my
> patch into the main Cairo git tree. Of course, I'm open to suggestions
> or changes if needed.
>
> I know this is quite a large patchset, but I plan even more improvements
> and bugfixes to Cairo's font/glyph handling; however it's probably better
> to submit them later, to avoid making the patchset even more complex that
> it currently is.
Hi David,
As I said in the meeting thread, I want to land this soon after 1.4.4 is
out, targeting 1.6.0 in July.
behdad
> Regards, and thanks in advance,
>
> - David Turner
>
>
> On Wed, 4 Apr 2007 19:00:52 +0200 (CEST), "Jan Slupski" <jslupski at juljas.net> said:
> >
> > Next issue:
> >
> > After brief looking at 1.4.2 it seems that David patches weren't merged.
> > Are there any plans to do so?
> >
> > Without this fix, heavy multithread testing still fails after few hours
> > (at least used to fail at Cairo 1.3.16).
> >
> > Thanks,
> > Jan
> >
> > Link to final version of the patch:
> > http://lists.freedesktop.org/archives/cairo/2007-March/009924.html
> >
> >
> > On Wed, 28 Feb 2007, David Turner wrote:
> >
> > > Hello,
> > >
> > > here's the first version of my patches to fix Cairo's usage of FreeType with multiple
> > > threads. It's rather big, so I'll summarize things here a little:
> > >
> > > - it's more or less a complete rewrite of the functionality, but it is
> > > API and ABI compatible with the original code.
> > >
> > > - there is no need to modify any client code, except the one using the broken
> > > cairo_ft_scaled_font_lock_face() and cairo_ft_scaled_font_unlock_face(),
> > > which probably means only Pango at the moment.
> > >
> > > normal users of Cairo should now be lock-free in all FreeType-related operations.
> > > no need for thread-specific list and other hacks like that by the way.
> > >
> > > - even if you use cairo_ft_scaled_font_lock_face() and cairo_ft_scaled_font_unlock_face(),
> > > you should be free from deadlocks with the rest of Cairo. that's because the returned
> > > FT_Face objects are allocated into a different library instance than the one used by
> > > the rest of the library.
> > >
> > > Of course, all hell breaks loose if two threads use FT_Face objects returned by
> > > cairo_ft_scaled_font_lock_face() at the same time, even if they're not the same
> > > FT_Face.
> > >
> > > The upgrade path to sanity is to use the functions named:
> > >
> > > cairo_freetype_state_lock()
> > > cairo_freetype_state_get_face()
> > > cairo_freetype_state_get_size()
> > > cairo_freetype_state_unlock()
> > >
> > > defined and documented in the new file cairo-freetype-state.c
> > >
> > >
> > > - there are now two backends: a FreeType-specific one, and a FontConfig-specific one.
> > > the only difference is that the FontConfig one is capable of implementing the
> > > toy interface, and is thus still the default on Unix.
> > >
> > > the idea is to be able to compile the FreeType backend on platforms where FontConfig
> > > is not available or desirable. Of course, the toy interface would then be implemented
> > > by the default backend for the platform, or simply not at all.
> > >
> > > - there are thus two additionnal public header files: "cairo-freetype.h" and
> > > "cairo-fontconfig.h", with corresponding functions using the surprisingly long
> > > "cairo_freetype_" and "cairo_fontconfig_" prefixes
> > >
> > > - this was done to avoid any conflict with the existing code and public headers.
> > > "cairo-ft.h" is still there and its functions are fully supported even if we
> > > can't make thread-safety guarantees for "locked" FT_Face usage.
> > >
> > > - the source code "cairo-ft-font.c" is still there, but is not compiled anymore.
> > > this is essentially for comparison purposes.
> > >
> > > - there are quite a few new source files as well:
> > >
> > > cairo-freetype-state.c (thread-safe FT_Face/FT_Size management)
> > > cairo-freetype-font.c (FreeType font backend)
> > > cairo-freetype-glyph.c (glyph loading + rendering + filtering)
> > > cairo-freetype.h (public FreeType backend APIs)
> > > cairo-freetype-private.h (guess what)
> > > cairo-fontconfig.h (public FontConfig backend APIs)
> > > cairo-fontconfig.c (tiny FontConfig font backend)
> > > cairo-ft.c (stubs to implement original cairo_ft_ functions)
> > >
> > > - I'd be happy to use shorter prefixes like "cairo_ft_" and "cairo_fc_" once
> > > Carl is happy with the implementation provided here. I wanted to be able to
> > > easily compare the new and the old code, and the different prefixes just
> > > makes things a lot easier there.
> > >
> > > - the cairo_ft_ functions do implement the current Cairo behaviour regarding
> > > font options (i.e. the FontConfig backend ignores user-provided options for
> > > antialiased setting, extracting those from the original FcPattern instead)
> > >
> > > since I still don't understand why this is a good thing, the cairo_freetype_
> > > and cairo_fontconfig_ equivalent functions to do implement this "feature",
> > > but this can easily be changed.
> > >
> > > (I plan to make a different email to discuss this issue in more details)
> > >
> > > - there is also a RATIONALE file that explains how certain things are implemented,
> > > that should make understanding the changes easier
> > >
> > > Finally, all test cases pass, except the ft-text-vertical-layout-* ones, but
> > > I believe it's because I don't have the relevant font files installed on my
> > > machine. Will check later.
> > >
> > > There has been a lot of shuffle during the intermediate commits that led to this
> > > patchset, so I recommend only studying the final changes, instead of the individual
> > > ones.
> > >
> > > Voila, you can find all this here:
> > >
> > > http://david.freetype.org/cairo/fix-freetype-usage-1.patchset.bz2
> > > http://david.freetype.org/cairo/RATIONALE
> > >
> > >
> > > Hope this helps,
> > >
> > > - David Turner
> > > - The FreeType Project (www.freetype.org)
> > > _______________________________________________
> > > cairo mailing list
> > > cairo at cairographics.org
> > > http://cairographics.org/cgi-bin/mailman/listinfo/cairo
> > >
> >
> > _ _ _ _ _____________________________________________
> > | |_| |\ | S L U P S K I jslupski at juljas.net
> > |_| | | | \| http://juljas.net/
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--
behdad
http://behdad.org/
"Those who would give up Essential Liberty to purchase a little
Temporary Safety, deserve neither Liberty nor Safety."
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