[OpenJDK 2D-Dev] Question regarding the integration of harfbuzz (JEP 258)

[Philip Race]

Hi Volker,

Running with ICU should stop harfbuzz use completely so if
you are still seeing a crash, perhaps it is due to something else entirely.
Especially since a "simple AWT program" should not load layout anyway.
There was a fair amount of new and changed code pushed recently ...

Yes, we need to run harfbuzz in multiple concurrent threads in the JDK.
A single threaded lock on harfbuzz would throttle text operations.
I suppose it is possible that we do not strictly need it as we currently 
create a
new harfbuzz "instance" each time we go to invoke layout but that
is something that at least theoretically could change.

The approach to synchronization is all from up-stream harfbuzz.
The harfbuzz mailing list might be the place to discuss that.
I'd expect it does work on AIX as a principal driver here is that
the IBM sponsored ICU project has deprecated its layout engine
and IBM/ICU are moving to harfbuzz so I'd be somewhat astonished
if they haven't yet tried it on AIX. Did you try just getting a copy
of the full hotspot library and running its configure on AIX to see if
harfbuzz can work out which options it wants there ? Obviously
I did not try that since I don't have AIX. Steven Loomis of IBM
who submitted the JEP should be able to help with a lot of this.

-phil.

On 12/8/15, 10:50 AM, Volker Simonis wrote:
> Hi,
>
> the integration of harfbuzz broke our AIX build because there's no
> implementation available for the hb_atomic macros in
> hb-atomic-private.hh. I've fixed that locally but still get a crash
> when running a simple AWT program (even with
> -Dsun.font.layoutengine=icu).
>
> I'm curretnly debugging the problem, but I have some general questions:
>
> 1. Do we really need the multi-threaded features of harfbuzz in OpenJDK?
>
> 2. Why does hurbuzz require these synchronization macros? From a first
> glance it doesn't seem to use multiple threads by itself. Does it have
> some global data structures which it needs to protect if harfbuzz is
> called from various threads?
>
> 3. Is there a way to test the hurfbuzz engine on a new platform? I saw
> the new test TestLayoutVsICU.java but it is marked as "manual" and it
> seems to require external fonts (at least some of which seem to be
> freely available). Could you please provide at least a minimal
> description on how this test can be run?
>
> 4. Is there a way to test that the implementation of the hb_atomic
> macros in hb-atomic-private.hh is correct (i.e. a way to stress
> harfbuzz from multiple threads)? I think this is important as I
> couldn't find a good description of the requirements for the atomic
> macros and on weak memory model architectures we should really get
> this right. For example there's no description of which fences are
> required around the various atomic operations. Getting this right
> across all platforms in the HotSpot (see
> hotspot/src/os_cpu/../vm/atomic_os_cp.inline.hpp) is already hard
> enough so I'm a little concerned that we are now introducing similar
> primitives in the class library.
>
> Thank you and best regards,
> Volker