[cairo] Cairo and multithreading einvironment.

[Andrea Canciani]

On Fri, Jul 22, 2011 at 2:48 AM, cu <cairouser at yahoo.com> wrote:
> Cairo seems to be getting "less" thread-safe as time goes on. We are
> using version 1.9.8 which we found to be most multithreading-friendly.
> We still have to serialize all text operations and of course no two
> threads can render to the same surface at the time. However, 1.9.8
> permits simultaneous rendering into separate surfaces and even allows
> the same source to be used for more than one surface at a time.
>
> Unfortunately every version after 1.9.8 was non-thread safe for all of
> the above operations - so we can't upgrade (probably ever, since there
> does not seem to be much effort in this direction).

The test suite checks the behavior of multithreaded drawing in pthread-*
tests.

The problem you describe should be solved in cairo master by

commit 71e8a4c23019b01aa43b334fcb2784c70daae9b5
Author: M Joonas Pihlaja <jpihlaja at cc.helsinki.fi>
Date:   Sat Feb 19 17:46:45 2011 +0200

    image: Avoid reusing pixman images for threadsafety.

    The pixman_image_ref() and pixman_image_unref() functions
    aren't threadsafe in current pixman, so we can't share
    pixman images across contexts where they may end up
    moving between threads.  The main use of these functions
    is in keeping a global cache of pixman_image_ts for
    solid colours and reusing the same pixman_image_t for
    patterns pointing to the same image data where possible.

    This patch removes those uses from cairo by wrapping
    them in a PIXMAN_HAS_ATOMIC_OPS conditional.  There is
    no automatic test this, so we will have to manually
    turn this code back on when pixman does gain atomic
    ops.

    The only two remaining calls to pixman_image_ref() are
    done on locally created images so they are safe.

    Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=34177

There is ongoing work into improving both the thread safety of
cairo and pixman and their multithreaded performance.

Andrea

PS: please report bugs (if possible with self-contained code to
reproduce the problem) for any remaining issues related to
multithreading. (I know of a couple of issues with multithreading
& snapshots, but afaict most of cairo should now be threadsafe)


>
> --cu
>
> Horodyski Marek (PZUZ) wrote:
>>
>> > -----Original Message-----
>>
>> > From: Horodyski Marek (PZUZ)
>>
>> > Sent: Friday, July 15, 2011 12:28 PM
>>
>> > To: cairo at cairographics.org
>>
>> > Subject: Cairo and multithreading einvironment.
>>
>> […]
>>
>> > Cairo works well in an sigle thread environment, but I have problems in
>>
>> > multi-threaded.
>>
>> When I use Cairo In MultiThread environment without mutex synchronize,
>> on monitor I see :
>>
>> cid:image002.png at 01CC1723.7C2D4EA0
>>
>> I can work with mutex synchronize, but but it costs time L
>>
>> Example code :
>>
>> hSurface := cairo_pdf_surface_create( "TEST.PDF", 566.9, 793.7 ) //
>> 200x280 mm in pt
>>
>> hCairo := cairo_create( hSurface )
>>
>> cairo_set_source_rgb( hCairo, 0, 0, 0 )
>>
>> cairo_select_font_face( hCairo, "verdana", CAIRO_FONT_SLANT_NORMAL, 0 )
>>
>> cairo_set_font_size( hCairo, 6 )
>>
>> cairo_move_to( hCairo, 1, 7 )
>>
>> cairo_show_text( hCairo, "Some text")
>>
>> ...
>>
>> cairo_show_page( hCairo )
>>
>> cairo_destroy( hCairo )
>>
>> cairo_surface_destroy( hSurface )
>>
>> String "TEST.PDF" in different thread are differ.
>>
>> Regards,
>>
>> Marek Horodyski
>>
>> ------------------------------------------------------------------------
>>
>> --
>> cairo mailing list
>> cairo at cairographics.org
>> http://lists.cairographics.org/mailman/listinfo/cairo
>
> --
> cairo mailing list
> cairo at cairographics.org
> http://lists.cairographics.org/mailman/listinfo/cairo
>