[cairo] fixing Cairo's FreeType multi-threaded usage

[David Turner]

Hello,

here's a second version of my patchset that fixes the bug described early
(incorrect behaviour of the FreeType-backed implementation of the toy font
interface). It needed a few tricky internal changes, but all sems good know.

  http://david.freetype.org/cairo/fix-freetype-usage-2.patchset

note that it was generated against a recent clone of the Cairo git repository,
you should *not* apply the first patchset before this one.

All test cases pass, except the ones that already failed with the original
sources.

As usual, all comments are welcomed :-)

- David



On Sat, 03 Mar 2007 19:22:34 +0100, "David Turner" <david at freetype.org> said:
> Hi again,
> 
> I found the bug, it only affects the implementation of the toy font
> interface,
> which is why I couldn't see it with my desktop (which uses Pango
> instead).
> 
> Simple profiling shows that all the slowdown comes from calling
> FontConfig
> matching algorithm in each iteration, while the original code cached the
> result correctly.
> 
> Basically, cairo_freetype_scaled_font_create_toy doesn't reference the
> parent
> toy font_face, but instead a new freetype font face that is created from
> the
> corresponding FontConfig pattern. As a consequence, the toy font face is
> destroyed when the function exits.
> 
> This shouldn't happen; I'll provide a new patchset shortly that fixes
> this
> issue.
> 
> Thanks a lot
> 
> - David
> 
> 
> On Sat, 3 Mar 2007 04:23:33 +0100 (CET), "Jan Slupski"
> <jslupski at juljas.net> said:
> > On Sat, 3 Mar 2007, David Turner wrote:
> > 
> > > no, this is not normal at all; I'm running my desktop on this patch and
> > > haven't seen any regression in performance. Are you sure your merge happened
> > > without conflicts ?
> > 
> > No, no conflicts. Only few 'fuzz'.
> > 
> > Except makefiles these are:
> > 
> > $ bzcat ../fix-freetype-usage-1.patchset.bz2 | patch -p1
> > (...)
> > patching file src/cairo-debug.c
> > Hunk #1 succeeded at 66 with fuzz 2.
> > (...)
> > patching file src/cairoint.h
> > Hunk #1 succeeded at 623 (offset 4 lines).
> > Hunk #3 succeeded at 1214 (offset 2 lines).
> > 
> > Should I try any earlier cairo snapshot?
> > 
> > > the long story is that some of the intermediate commits in the patchset do
> > > produce correct behaviour and very poor performance, but this is normally
> > > fixed in later ones.
> > >
> > > In the event your merge didn't work correctly, you could be left in one of
> > > these hideously slow cases. I've just checked the patchset file, and the
> > > changes described there seem ok.
> > >
> > > Could you give more details about your test cases ? it may be interesting.
> > 
> > Seems that I am able to reproduce these on my simple cairo threads test
> > case
> > I used before to hunt previous problems. (attached)
> > 
> > Cairo-git:
> > real    0m2.551s
> > user    0m2.530s
> > sys     0m0.020s
> > 
> > Cairo-git + fix-freetype-usage-1.patchset:
> > real    0m12.956s
> > user    0m12.950s
> > sys     0m0.010s
> > 
> > Command used: time ./threads 1 10000 
> > (one thread, 10K loops)
> > 
> > 
> > Before I used two samples (against some external library that calls
> > cairo) on two Linux machines. Slowdown with patch applied was:
> > - between 2x (x86_64 dual) and 6x (i386) - first sample
> > - between 6x (x86_64 dual) and 60x+ (i386) really! - another sample
> > 
> > I'm sure about these results, but if you find them unbelivable
> > and cannot reproduce, I'll repeat tests from scratch to make it 200%
> > sure...
> > 
> > 
> > Thanks a lot,
> > Jan
> > 
> > 
> > 
> > > On Sat, 3 Mar 2007 01:47:49 +0100 (CET), "Jan Slupski" <jslupski at juljas.net> said:
> > >> 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:
> > >>
> > >> Hi David,
> > >>
> > >> I tried your patches against the current git cairo (latest commit
> > >> fed13e77e1de071ddaaf829aced10b02f6bc8c90).
> > >>
> > >> Is it expected that cairo with these patches runs *much* slower
> > >> than without? I'm running simple test case and it seems to be
> > >> 8+ times slower even in single thread.
> > >>
> > >> Is there anything special I should do (i.e. revert some already
> > >> merged patches)?
> > >>
> > >> I'll try to figure out what exactly caused the slowdown, but any hints
> > >> are apperciated...
> > >>
> > >> I have used default setup (./autogen.sh; make) and
> > >> fontconfig 2.4.2, freetype 2.1.7 & 2.3.1
> > 
> >     _  _  _  _  _____________________________________________
> >     | |_| |\ |  S L U P S K I             jslupski at juljas.net
> >   |_| | | | \|                             http://juljas.net/
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